initial import of the C runtime

57 files changed, 7468 insertions, 0 deletions

diff --git a/src/runtime/c/gu/assert.c b/src/runtime/c/gu/assert.c
new file mode 100644
index 000000000..e111912d3
--- /dev/null
+++ b/src/runtime/c/gu/assert.c
@@ -0,0 +1,53 @@
+#include <gu/assert.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdarg.h>
+
+const char*
+gu_assert_mode_descs[] = {
+	[GU_ASSERT_PRECOND] = "precondition failed",
+	[GU_ASSERT_POSTCOND] = "postcondition failed",
+	[GU_ASSERT_ASSERTION] = "assertion failed",
+	[GU_ASSERT_NEVER] = "control should not reach here",
+};
+
+void
+gu_abort_v_(GuAssertMode mode,
+	    const char* file, const char* func, int line,
+	    const char* msg_fmt, va_list args)
+{
+	const char* desc = gu_assert_mode_descs[mode];
+	(void) fprintf(stderr, "%s (%s:%d): %s\n", func, file, line, desc);
+	if (msg_fmt != NULL) {
+		(void) fputc('\t', stderr);
+		(void) vfprintf(stderr, msg_fmt, args);
+		(void) fputc('\n', stderr);
+	}
+	abort();
+}
+
+void
+gu_abort_(GuAssertMode mode,
+	  const char* file, const char* func, int line,
+	  const char* msg_fmt, ...)
+{
+	va_list args;
+	va_start(args, msg_fmt);
+	gu_abort_v_(mode, file, func, line, msg_fmt, args);
+	va_end(args);
+}
+	
+
+void 
+gu_fatal(const char* fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	fputs("Fatal error", stderr);
+	if (fmt) {
+		fputs(": ", stderr);
+		(void) vfprintf(stderr, fmt, args);
+	}
+	fputc('\n', stderr);
+	abort();
+}
diff --git a/src/runtime/c/gu/assert.h b/src/runtime/c/gu/assert.h
new file mode 100644
index 000000000..9d7ecc15f
--- /dev/null
+++ b/src/runtime/c/gu/assert.h
@@ -0,0 +1,61 @@
+#ifndef GU_ASSERT_H_
+#define GU_ASSERT_H_
+
+#include <gu/defs.h>
+
+typedef enum {
+	GU_ASSERT_PRECOND,
+	GU_ASSERT_ASSERTION,
+	GU_ASSERT_POSTCOND,
+	GU_ASSERT_NEVER
+} GuAssertMode;
+
+void
+gu_abort_v_(GuAssertMode mode, 
+	    const char* file, const char* func, int line,
+	    const char* msg_fmt, va_list args);
+
+void
+gu_abort_(GuAssertMode mode, 
+	  const char* file, const char* func, int line,
+	  const char* msg_fmt, ...);
+
+#ifndef NDEBUG
+#define gu_assertion_(mode_, expr_, ...) \
+	GU_BEGIN							\
+	if (!(expr_)) {							\
+		gu_abort_(mode_, __FILE__, __func__, __LINE__, __VA_ARGS__);	\
+	}								\
+	GU_END
+#else
+// this should prevent unused variable warnings when a variable is only used
+// in an assertion
+#define gu_assertion_(mode_, expr_, ...)	\
+	GU_BEGIN				\
+	(void) (sizeof (expr_));		\
+	GU_END
+#endif
+
+
+#define gu_require(expr)				\
+	gu_assertion_(GU_ASSERT_PRECOND, expr, "%s", #expr)
+
+#define gu_assert_msg(expr, ...)				\
+	gu_assertion_(GU_ASSERT_ASSERTION, expr, __VA_ARGS__)
+
+#define gu_assert(expr)				\
+	gu_assert_msg(expr, "%s", #expr)
+
+#define gu_ensure(expr)						\
+	gu_assertion_(GU_ASSERT_POSTCOND, expr, "%s", #expr)
+
+#define gu_impossible_msg(...)			\
+	gu_assertion_(GU_ASSERT_ASSERTION, false, __VA_ARGS__)
+
+#define gu_impossible()				\
+	gu_impossible_msg(NULL)
+
+void 
+gu_fatal(const char* fmt, ...);
+
+#endif /* GU_ASSERT_H_ */
diff --git a/src/runtime/c/gu/bits.c b/src/runtime/c/gu/bits.c
new file mode 100644
index 000000000..9126b0448
--- /dev/null
+++ b/src/runtime/c/gu/bits.c
@@ -0,0 +1,53 @@
+#include <gu/bits.h>
+
+#include <limits.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <math.h>
+
+unsigned gu_ceil2e(unsigned u)  
+{
+	u--;
+	u |= u >> 1;
+	u |= u >> 2;
+	u |= u >> 4;
+	u |= u >> 8;
+#if UINT_MAX > UINT16_MAX
+	u |= u >> 16;
+#endif
+#if UINT_MAX > UINT32_MAX
+	u |= u >> 32;
+#endif
+	u++;
+	return u;
+}
+
+GU_DEFINE_TYPE(GuIntDecodeExn, abstract, _);
+
+double 
+gu_decode_double(uint64_t u)
+{
+	bool sign = u >> 63;
+	unsigned rawexp = u >> 52 & 0x7ff;
+	uint64_t mantissa = u & 0xfffffffffffff;
+	double ret;
+
+	if (rawexp == 0x7ff) {
+		if (mantissa == 0) {
+			ret = INFINITY;
+		} else {
+			// At least glibc supports specifying the
+			// mantissa like this.
+			int len = snprintf(NULL, 0, "0x%" PRIx64, mantissa);
+			char buf[len + 1];
+			snprintf(buf, len + 1, "0x%" PRIx64, mantissa);
+			ret = nan(buf);
+		}
+	} else {
+		uint64_t m = rawexp ? 1ULL << 52 | mantissa : mantissa << 1;
+		ret = ldexp((double) m, rawexp - 1075);
+	}
+	return sign ? copysign(ret, -1.0) : ret;
+}
diff --git a/src/runtime/c/gu/bits.h b/src/runtime/c/gu/bits.h
new file mode 100644
index 000000000..9ba1b0c8e
--- /dev/null
+++ b/src/runtime/c/gu/bits.h
@@ -0,0 +1,151 @@
+#ifndef GU_BITS_H_
+#define GU_BITS_H_
+
+#include <gu/defs.h>
+#include <gu/assert.h>
+
+
+#define GU_WORD_BITS (sizeof(GuWord) * CHAR_BIT)
+
+
+/*
+ * Based on the Bit Twiddling Hacks collection by Sean Eron Anderson
+ * <http://graphics.stanford.edu/~seander/bithacks.html>
+ */
+
+unsigned gu_ceil2e(unsigned i);
+
+static inline int
+gu_sign(int i) {
+	return (i > 0) - (i < 0);
+}
+
+static inline size_t
+gu_ceildiv(size_t size, size_t div)
+{
+	return (size + div - 1) / div;
+}
+
+static inline bool
+gu_aligned(uintptr_t addr, size_t alignment)
+{
+	gu_require(alignment == gu_ceil2e(alignment));
+	return (addr & (alignment - 1)) == 0;
+}
+
+static inline uintptr_t
+gu_align_forward(uintptr_t addr, size_t alignment) {
+	gu_require(alignment == gu_ceil2e(alignment));
+	uintptr_t mask = alignment - 1;
+	return (addr + mask) & ~mask;
+}
+
+static inline uintptr_t
+gu_align_backward(uintptr_t addr, size_t alignment) {
+	gu_require(alignment == gu_ceil2e(alignment));
+	return addr & ~(alignment - 1);
+}
+
+static inline bool
+gu_bits_test(const GuWord* bitmap, int idx) {
+	return !!(bitmap[idx / GU_WORD_BITS] & 1 << (idx % GU_WORD_BITS));
+}
+
+static inline void
+gu_bits_set(GuWord* bitmap, int idx) {
+	bitmap[idx / GU_WORD_BITS] |= ((GuWord) 1) << (idx % GU_WORD_BITS);
+}
+
+static inline void
+gu_bits_clear(GuWord* bitmap, int idx) {
+	bitmap[idx / GU_WORD_BITS] &= ~(((GuWord) 1) << (idx % GU_WORD_BITS));
+}
+
+static inline size_t
+gu_bits_size(size_t n_bits) {
+	return gu_ceildiv(n_bits, GU_WORD_BITS) * sizeof(GuWord);
+}
+
+static inline void*
+gu_word_ptr(GuWord w)
+{
+	return (void*) w;
+}
+
+static inline GuWord
+gu_ptr_word(void* p)
+{
+	return (GuWord) p;
+}
+
+#define GuOpaque() struct { GuWord w_; }
+
+typedef GuWord GuTagged;
+
+#define GU_TAG_MAX (sizeof(GuWord) - 1)
+
+static inline size_t
+gu_tagged_tag(GuTagged t) {
+	return (int) (t & (sizeof(GuWord) - 1));
+}
+
+static inline void*
+gu_tagged_ptr(GuTagged w) {
+	return (void*) gu_align_backward(w, sizeof(GuWord));
+}
+
+static inline GuTagged
+gu_tagged(void* ptr, size_t tag) {
+	gu_require(tag < sizeof(GuWord));
+	uintptr_t u = (uintptr_t) ptr;
+	gu_require(gu_align_backward(u, sizeof(GuWord)) == u);
+	return (GuWord) { u | tag };
+}
+
+#include <gu/exn.h>
+#include <gu/type.h>
+
+extern GU_DECLARE_TYPE(GuIntDecodeExn, abstract);
+
+#define GU_DECODE_2C_(u_, t_, umax_, posmax_, tmin_, err_)	\
+	(((u_) <= (posmax_))					\
+	 ? (t_) (u_)						\
+	 : (tmin_) + ((t_) ((umax_) - (u_))) < 0		\
+	 ? -1 - ((t_) ((umax_) - (u_)))				\
+	 : (gu_raise(err_, GuIntDecodeExn), -1))
+
+
+static inline int8_t
+gu_decode_2c8(uint8_t u, GuExn* err)
+{
+	return GU_DECODE_2C_(u, int8_t, UINT8_C(0xff), 
+			     INT8_C(0x7f), INT8_MIN, err);
+}
+
+static inline int16_t
+gu_decode_2c16(uint16_t u, GuExn* err)
+{
+	return GU_DECODE_2C_(u, int16_t, UINT16_C(0xffff), 
+			     INT16_C(0x7fff), INT16_MIN, err);
+}
+
+static inline int32_t
+gu_decode_2c32(uint32_t u, GuExn* err)
+{
+	return GU_DECODE_2C_(u, int32_t, UINT32_C(0xffffffff), 
+			     INT32_C(0x7fffffff), INT32_MIN, err);
+}
+
+static inline int64_t
+gu_decode_2c64(uint64_t u, GuExn* err)
+{
+	return GU_DECODE_2C_(u, int64_t, UINT64_C(0xffffffffffffffff), 
+			     INT64_C(0x7fffffffffffffff), INT64_MIN, err);
+}
+
+double
+gu_decode_double(uint64_t u);
+
+
+
+#endif // GU_BITS_H_
diff --git a/src/runtime/c/gu/choice.c b/src/runtime/c/gu/choice.c
new file mode 100644
index 000000000..b1e4a3a5e
--- /dev/null
+++ b/src/runtime/c/gu/choice.c
@@ -0,0 +1,73 @@
+#include <gu/choice.h>
+#include <gu/seq.h>
+#include <gu/assert.h>
+#include <gu/log.h>
+
+struct GuChoice {
+	GuBuf* path;
+	size_t path_idx;
+};
+
+GuChoice*
+gu_new_choice(GuPool* pool)
+{
+	GuChoice* ch = gu_new(GuChoice, pool);
+	ch->path = gu_new_buf(uint8_t, pool);
+	ch->path_idx = 0;
+	return ch;
+}
+
+GuChoiceMark
+gu_choice_mark(GuChoice* ch)
+{
+	gu_assert(ch->path_idx <= gu_buf_length(ch->path));
+	gu_debug("%p@%d: mark", ch, ch->path_idx);
+	return (GuChoiceMark){ch->path_idx};
+}
+
+void
+gu_choice_reset(GuChoice* ch, GuChoiceMark mark)
+{
+	gu_assert(ch->path_idx <= gu_buf_length(ch->path));
+	gu_debug("%p@%d: reset %d", ch, ch->path_idx, mark.path_idx);
+	gu_require(mark.path_idx <= ch->path_idx );
+	ch->path_idx = mark.path_idx;
+}
+
+int
+gu_choice_next(GuChoice* ch, int n_choices)
+{
+	gu_assert(n_choices >= 0);
+	gu_require(n_choices <= UINT8_MAX);
+	gu_assert(ch->path_idx <= gu_buf_length(ch->path));
+	if (n_choices == 0) {
+		return -1;
+	}
+	int i = 0;
+	if (gu_buf_length(ch->path) > ch->path_idx) {
+		i = (int) gu_buf_get(ch->path, uint8_t, ch->path_idx);
+		gu_assert(i <= n_choices);
+	} else {
+		gu_buf_push(ch->path, uint8_t, n_choices);
+		i = n_choices;
+	}
+	int ret = (i == 0) ? -1 : n_choices - i;
+	gu_debug("%p@%d: %d", ch, ch->path_idx, ret);
+	ch->path_idx++;
+	return ret;
+}
+
+bool
+gu_choice_advance(GuChoice* ch)
+{
+	gu_assert(ch->path_idx <= gu_buf_length(ch->path));
+	
+	while (gu_buf_length(ch->path) > ch->path_idx) {
+		uint8_t last = gu_buf_pop(ch->path, uint8_t);
+		if (last > 1) {
+			gu_buf_push(ch->path, uint8_t, last-1);
+			return true;
+		}
+	}
+	return false;
+}
diff --git a/src/runtime/c/gu/choice.h b/src/runtime/c/gu/choice.h
new file mode 100644
index 000000000..aea76dde8
--- /dev/null
+++ b/src/runtime/c/gu/choice.h
@@ -0,0 +1,37 @@
+#ifndef GU_CHOICE_H_
+#define GU_CHOICE_H_
+
+#include <gu/mem.h>
+
+typedef struct GuChoice GuChoice;
+
+typedef struct GuChoiceMark GuChoiceMark;
+
+GuChoice*
+gu_new_choice(GuPool* pool);
+
+int
+gu_choice_next(GuChoice* ch, int n_choices);
+
+GuChoiceMark
+gu_choice_mark(GuChoice* ch);
+
+void
+gu_choice_reset(GuChoice* ch, GuChoiceMark mark);
+
+bool
+gu_choice_advance(GuChoice* ch);
+
+
+// private
+
+struct GuChoiceMark {
+	size_t path_idx;
+};
+
+
+
+
+
+
+#endif // GU_CHOICE_H_
diff --git a/src/runtime/c/gu/defs.c b/src/runtime/c/gu/defs.c
new file mode 100644
index 000000000..2c3772b7c
--- /dev/null
+++ b/src/runtime/c/gu/defs.c
@@ -0,0 +1,4 @@
+#include <gu/defs.h>
+
+void* const gu_null = NULL;
+GuStruct* const gu_null_struct = NULL;
diff --git a/src/runtime/c/gu/defs.h b/src/runtime/c/gu/defs.h
new file mode 100644
index 000000000..9fa62b39b
--- /dev/null
+++ b/src/runtime/c/gu/defs.h
@@ -0,0 +1,217 @@
+/* 
+ * Copyright 2010 University of Helsinki.
+ *   
+ * This file is part of libgu.
+ * 
+ * Libgu is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ * 
+ * Libgu is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with libgu. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ *
+ * Miscellaneous macros.
+ */
+
+#ifndef GU_DEFS_H_
+#define GU_DEFS_H_
+
+#include <stddef.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <limits.h>
+#include <stdarg.h>
+#include <gu/sysdeps.h>
+
+#define gu_container(mem_p, container_type, member) \
+	((container_type*)(((uint8_t*) (mem_p)) - offsetof(container_type, member)))
+/**< Find the address of a containing structure.
+ *
+ * If @c s has type @c t*, where @c t is a struct or union type with a
+ * member @m, then <tt>GU_CONTAINER_P(&s->m, t, m) == s</tt>.
+ * 
+ * @param mem_p           Pointer to the member of a structure.
+ * @param container_type  The type of the containing structure.
+ * @param member          The name of the member of @a container_type
+ * @return  The address of the containing structure.
+ *
+ * @hideinitializer */
+
+
+#define gu_member_p(struct_p_, offset_)		\
+	((void*)&((uint8_t*)(struct_p_))[offset_])
+
+#define gu_member(t_, struct_p_, offset_) \
+	(*(t_*)gu_member_p(struct_p_, offset_))
+
+#ifdef GU_ALIGNOF
+# define gu_alignof GU_ALIGNOF
+# define GU_ALIGNOF_WORKS_ON_FAM_STRUCTS
+#else
+# define gu_alignof(t_) \
+	((size_t)(offsetof(struct { char c_; t_ e_; }, e_)))
+# ifdef GU_CAN_HAVE_FAM_IN_MEMBER
+#  define GU_ALIGNOF_WORKS_ON_FAM_STRUCTS
+# endif
+#endif
+
+#define GU_PLIT(type, expr) \
+	((type[1]){ expr })
+
+#define GU_LVALUE(type, expr) \
+	(*((type[1]){ expr }))
+
+#define GU_COMMA ,
+
+#define GU_ARRAY_LEN(t,a) (sizeof((const t[])a) / sizeof(t))
+
+#define GU_ID(...) __VA_ARGS__
+
+// This trick is by Laurent Deniau <laurent.deniau@cern.ch>
+#define GU_N_ARGS(...)				\
+	GU_N_ARGS_(__VA_ARGS__,						\
+		   31,30,29,28,27,26,25,24,				\
+		   23,22,21,20,19,18,17,16,				\
+		   15,14,13,12,11,10,9,8,				\
+		   7,6,5,4,3,2,1,0)					
+#define GU_N_ARGS_(...) GU_N_ARGS__(__VA_ARGS__)
+#define GU_N_ARGS__(a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,			\
+		    q,r,s,t,u,v,w,x,y,z,aa,ab,ac,ad,ae,N,...)		\
+	N
+
+#define GU_ARG1(a1, ...) a1
+#define GU_ARG2(a1, a2, ...) a2
+
+#define GU_BEGIN do {
+#define GU_END } while (false)
+
+#define GU_NOP GU_BEGIN (void) 0; GU_END
+
+/**< @hideinitializer */
+
+//
+// Assert
+//
+
+#define GU_MAX(a_, b_) ((a_) > (b_) ? (a_) : (b_))
+#define GU_MIN(a_, b_) ((a_) < (b_) ? (a_) : (b_))
+
+static inline int
+gu_max(int a, int b) {
+	return GU_MAX(a, b);
+}
+
+static inline int
+gu_min(int a, int b) {
+	return GU_MIN(a, b);
+}
+
+#ifdef GU_ALIGNOF_WORKS_ON_FAM_STRUCTS
+#define gu_flex_alignof gu_alignof
+#else
+#define gu_flex_alignof(t) 0
+#endif
+
+static inline size_t
+gu_flex_size(size_t ssize, size_t offset, int n_elems, size_t e_size)
+{
+	return GU_MAX(ssize, offset + n_elems * e_size);
+}
+
+#define GU_FLEX_SIZE(type, flex_member, n_elems)			\
+	gu_flex_size(sizeof(type), offsetof(type, flex_member),		\
+		     n_elems, sizeof(((type*)NULL)->flex_member[0]))
+
+
+// The following are directly from gmacros.h in GLib
+
+#define GU_PASTE_ARGS(id1_,id2_)	\
+	id1_ ## id2_
+
+#define GU_PASTE(id1_, id2_)			\
+	GU_PASTE_ARGS(id1_, id2_)
+
+#define GU_STATIC_ASSERT(expr_)						\
+	typedef struct {						\
+		char static_assert[(expr_) ? 1 : -1];			\
+	} GU_PASTE(GuStaticAssert_, __LINE__)
+
+
+#define GU_ENSURE_TYPE(T, EXPR)			\
+	((void)(sizeof(*(T*)NULL=(EXPR))),(EXPR))
+
+#define GU_END_DECLS \
+	extern void gu_dummy_(void)
+
+extern void* const gu_null;
+
+// Dummy struct used for generic struct pointers
+typedef struct GuStruct GuStruct;
+
+extern GuStruct* const gu_null_struct;
+
+typedef uintptr_t GuWord;
+
+#define GU_WORD_MAX UINTPTR_MAX
+
+// TODO: use max_align_t once C1X is supported
+typedef union {
+	char c;
+	short s;
+	int i;
+	long l;
+	long long ll;
+	intmax_t im;
+	float f;
+	double d;
+	long double ld;
+	void* p;
+	void (*fp)();
+} GuMaxAlign;
+
+#define gu_alloca(N)				\
+	(((union { GuMaxAlign align_; uint8_t buf_[N]; }){{0}}).buf_)
+
+
+// For Doxygen
+#define GU_PRIVATE /** @private */
+
+#ifdef GU_GNUC
+# define GU_LIKELY(EXPR) __builtin_expect(EXPR, 1)
+# define GU_UNLIKELY(EXPR) __builtin_expect(EXPR, 0)
+# define GU_IS_CONSTANT(EXPR) __builtin_constant_p(EXPR)
+#else
+# define GU_LIKELY(EXPR) (EXPR)
+# define GU_UNLIKELY(EXPR) (EXPR)
+# ifdef GU_OPTIMIZE_SIZE
+#  define GU_IS_CONSTANT(EXPR) false
+# else
+#  define GU_IS_CONSTANT(EXPR) true
+# endif
+#endif
+
+// Splint annotations
+#define GU_ONLY GU_SPLINT(only)
+#define GU_NULL GU_SPLINT(null)
+#define GU_NOTNULL GU_SPLINT(notnull) 
+#define GU_RETURNED GU_SPLINT(returned)
+#define GU_ABSTRACT GU_SPLINT(abstract)
+#define GU_IMMUTABLE GU_SPLINT(immutable)
+#define GU_NOTREACHED GU_SPLINT(notreached)
+#define GU_UNUSED GU_SPLINT(unused) GU_GNUC_ATTR(unused)
+#define GU_OUT GU_SPLINT(out)
+#define GU_IN GU_SPLINT(in)
+#define GU_NORETURN GU_SPLINT(noreturn) GU_GNUC_ATTR(noreturn)
+#define GU_MODIFIES(x) GU_SPLINT(modifies x)
+
+#endif // GU_DEFS_H_
diff --git a/src/runtime/c/gu/dump.c b/src/runtime/c/gu/dump.c
new file mode 100644
index 000000000..0329f5932
--- /dev/null
+++ b/src/runtime/c/gu/dump.c
@@ -0,0 +1,411 @@
+#include <gu/dump.h>
+#include <gu/list.h>
+#include <gu/variant.h>
+#include <gu/seq.h>
+#include <gu/assert.h>
+#include <gu/str.h>
+#include <gu/file.h>
+
+GuDump*
+gu_new_dump(GuWriter* wtr, GuTypeTable* dumpers, GuExn* err, GuPool* pool)
+{
+	GuDump* ctx = gu_new(GuDump, pool);
+	ctx->pool = pool;
+	if (dumpers == NULL) {
+		dumpers = &gu_dump_table;
+	}
+	ctx->dumpers = gu_new_type_map(dumpers, pool);
+	ctx->yaml = gu_new_yaml(wtr, err, pool);
+	ctx->data = gu_new_addr_map(void, void*, &gu_null, pool);
+	ctx->print_address = false;
+	return ctx;
+}
+
+void
+gu_dump(GuType* type, const void* value, GuDump* ctx)
+{
+	GuDumpFn* dumper = gu_type_map_get(ctx->dumpers, type);
+	if (ctx->print_address) {
+		GuPool* pool = gu_new_pool();
+		GuString s = gu_format_string(pool, "%p", value);
+		gu_yaml_comment(ctx->yaml, s);
+		gu_pool_free(pool);
+	}
+	(*dumper)(dumper, type, value, ctx);
+}
+
+void
+gu_dump_stderr(GuType* type, const void* value, GuExn* err)
+{
+	GuPool* pool = gu_new_pool();
+	GuOut* out = gu_file_out(stderr, pool);
+#if 0
+	GuWriter* wtr = gu_locale_writer(out, pool);
+#else
+	GuWriter* wtr = gu_new_utf8_writer(out, pool);
+#endif
+	GuDump* ctx = gu_new_dump(wtr, NULL, err, pool);
+	gu_dump(type, value, ctx);
+	gu_pool_free(pool);
+}
+
+static void
+gu_dump_scalar(GuDump* ctx, const char* fmt, ...)
+{
+	GuPool* tmp_pool = gu_local_pool();
+	va_list args;
+	va_start(args, fmt);
+	GuString s = gu_format_string_v(fmt, args, tmp_pool);
+	va_end(args);
+	gu_yaml_scalar(ctx->yaml, s);
+	gu_pool_free(tmp_pool);
+}
+
+static void
+gu_dump_str_scalar(GuDump* ctx, const char* str)
+{
+	GuPool* tmp_pool = gu_local_pool();
+	GuString s = gu_str_string(str, tmp_pool);
+	gu_yaml_scalar(ctx->yaml, s);
+	gu_pool_free(tmp_pool);
+}
+
+static void
+gu_dump_null(GuDump* ctx)
+{
+	gu_yaml_tag_secondary(ctx->yaml, "null");
+	gu_yaml_scalar(ctx->yaml, gu_empty_string);
+}
+
+static void 
+gu_dump_int(GuDumpFn* dumper, GuType* type, const void* p, 
+	    GuDump* ctx)
+{
+	(void) dumper;
+	(void) type;
+	const int* ip = p;
+	gu_dump_scalar(ctx, "%d", *ip);
+}
+
+static void 
+gu_dump_uint16(GuDumpFn* dumper, GuType* type, const void* p, 
+	       GuDump* ctx)
+{
+	(void) dumper;
+	(void) type;
+	const uint16_t* ip = p;
+	gu_dump_scalar(ctx, "%" PRIu16, *ip);
+}
+
+static void 
+gu_dump_size(GuDumpFn* dumper, GuType* type, const void* p, 
+	     GuDump* ctx)
+{
+	(void) (dumper && type);
+	const size_t* zp = p;
+	gu_dump_scalar(ctx, "%zu", *zp);
+}
+
+
+
+static void 
+gu_dump_double(GuDumpFn* dumper, GuType* type, const void* p, 
+	       GuDump* ctx)
+{
+	(void) dumper;
+	(void) type;
+	const double* dp = p;
+	gu_dump_scalar(ctx, "%lf", *dp);
+}
+
+static const char gu_dump_length_key[] = "gu_dump_length_key";
+
+static void 
+gu_dump_length(GuDumpFn* dumper, GuType* type, const void* p, 
+	       GuDump* ctx)
+{
+	(void) dumper;
+	(void) type;
+	const GuLength* ip = p;
+	gu_dump_scalar(ctx, "%d", *ip);
+	GuLength* lenp = gu_map_get(ctx->data, gu_dump_length_key, void*);
+	if (lenp != NULL) {
+		*lenp = *ip;
+	}
+}
+
+static void 
+gu_dump_str(GuDumpFn* dumper, GuType* type, const void* p, 
+	    GuDump* ctx)
+{
+	(void) dumper;
+	(void) type;
+	const GuStr* sp = p;
+	gu_dump_str_scalar(ctx, *sp);
+}
+
+static void 
+gu_dump_string(GuDumpFn* dumper, GuType* type, const void* p, 
+	       GuDump* ctx)
+{
+	(void) dumper;
+	(void) type;
+	const GuString* sp = p;
+	gu_yaml_scalar(ctx->yaml, *sp);
+}
+
+
+// For _non-shared_ pointers.
+static void 
+gu_dump_pointer(GuDumpFn* dumper, GuType* type, const void* p, 
+		GuDump* ctx)
+{
+	(void) dumper;
+	GuPointerType* ptype = (GuPointerType*) type;
+	void* const* pp = p;
+	if (*pp == NULL) {
+		gu_dump_null(ctx);
+	} else {
+		gu_dump(ptype->pointed_type, *pp, ctx);
+	}
+}
+
+typedef struct {
+	GuMapItor itor;
+	GuMapType* mtype;
+	GuDump* ctx;
+} GuDumpMapFn;
+
+static void
+gu_dump_map_itor(GuMapItor* self, const void* key, void* value, GuExn* err)
+{
+	(void) err;
+	GuDumpMapFn* clo = (GuDumpMapFn*) self;
+	gu_dump(clo->mtype->key_type, key, clo->ctx);
+	gu_dump(clo->mtype->value_type, value, clo->ctx);
+}
+
+static void
+gu_dump_map(GuDumpFn* dumper, GuType* type, const void* p,
+	    GuDump* ctx)
+{
+	(void) dumper;
+	GuMapType* mtype = (GuMapType*) type;
+	GuMap* map = (GuMap*) p;
+	gu_yaml_begin_mapping(ctx->yaml);
+	GuDumpMapFn clo = { { gu_dump_map_itor }, mtype, ctx };
+	gu_map_iter(map, &clo.itor, NULL);
+	gu_yaml_end(ctx->yaml);
+}
+
+
+static void
+gu_dump_struct(GuDumpFn* dumper, GuType* type, const void* p,
+	       GuDump* ctx)
+{
+	(void) dumper;
+	GuStructRepr* srepr = (GuStructRepr*) type;
+	gu_yaml_begin_mapping(ctx->yaml);
+	const uint8_t* data = p;
+	GuLength* old_lenp = gu_map_get(ctx->data, gu_dump_length_key, void*);
+	GuLength len = (GuLength)-1;
+	gu_map_put(ctx->data, gu_dump_length_key, void*, &len);
+
+	for (int i = 0; i < srepr->members.len; i++) {
+		const GuMember* member = &srepr->members.elems[i];
+		gu_dump_str_scalar(ctx, member->name);
+		const uint8_t* memp = &data[member->offset];
+		if (member->is_flex) {
+			// Flexible array member
+			gu_assert(len != (GuLength)-1);
+			size_t mem_s = gu_type_size(member->type);
+			gu_yaml_begin_sequence(ctx->yaml);
+			for (GuLength i = 0; i < len; i++) {
+				gu_dump(member->type, &memp[i * mem_s], ctx);
+			}
+			gu_yaml_end(ctx->yaml);
+		} else {
+			gu_dump(member->type, memp, ctx);
+		}
+	}
+	gu_yaml_end(ctx->yaml);
+	if (old_lenp) {
+		gu_map_set(ctx->data, gu_dump_length_key, void*, old_lenp);
+	}
+}
+
+static void
+gu_dump_alias(GuDumpFn* dumper, GuType* type, const void* p,
+	      GuDump* ctx)
+{
+	(void) dumper;
+	GuTypeAlias* alias = gu_type_cast(type, alias);
+
+	gu_dump(alias->type, p, ctx);
+}
+
+static const char gu_dump_reference_key[] = "reference";
+
+static bool
+gu_dump_anchor(GuDump* ctx, const void* p) 
+{
+	GuMap* map = gu_map_get(ctx->data, gu_dump_reference_key, void*);
+	if (map == NULL) {
+		map = gu_new_addr_map(void, GuYamlAnchor,
+				      &gu_yaml_null_anchor, ctx->pool);
+		gu_map_put(ctx->data, gu_dump_reference_key, void*, map);
+	}
+	GuYamlAnchor a = gu_map_get(map, p, GuYamlAnchor);
+	if (a == gu_yaml_null_anchor) {
+		a = gu_yaml_anchor(ctx->yaml);
+		gu_map_put(map, p, GuYamlAnchor, a);
+		return true;
+	} else {
+		gu_yaml_alias(ctx->yaml, a);
+		return false;
+	}
+}
+
+static void
+gu_dump_referenced(GuDumpFn* dumper, GuType* type, const void* p,
+		   GuDump* ctx)
+{
+	(void) dumper;
+	GuTypeAlias* alias = gu_type_cast(type, alias);
+	bool created = gu_dump_anchor(ctx, p);
+	if (created) {
+		gu_dump(alias->type, p, ctx);
+	} else {
+		// gu_assert(false);
+	}
+}
+
+static void 
+gu_dump_reference(GuDumpFn* dumper, GuType* type, const void* p, 
+		  GuDump* ctx)
+{
+	(void) dumper;
+	(void) type;
+	void* const* pp = p;
+	bool created = gu_dump_anchor(ctx, *pp);
+	if (created) {
+		// gu_assert(false);
+		GuPointerType* ptype = (GuPointerType*) type;
+		gu_dump(ptype->pointed_type, *pp, ctx);
+	}
+}
+
+static void 
+gu_dump_shared(GuDumpFn* dumper, GuType* type, const void* p, 
+		  GuDump* ctx)
+{
+	(void) dumper;
+	void* const* pp = p;
+	if (*pp == NULL) {
+		gu_dump_null(ctx);
+	} else {
+		bool created = gu_dump_anchor(ctx, *pp);
+		if (created) {
+			GuPointerType* ptype = (GuPointerType*) type;
+			gu_dump(ptype->pointed_type, *pp, ctx);
+		}
+	}
+}
+
+static void 
+gu_dump_list(GuDumpFn* dumper, GuType* type, const void* p, 
+	     GuDump* ctx)
+{
+	(void) dumper;
+	GuListType* ltype = (GuListType*) type;
+	const uint8_t* up = p;
+	int len = * (const int*) p;
+	size_t elem_size = gu_type_size(ltype->elem_type);
+	gu_yaml_begin_sequence(ctx->yaml);
+	for (int i = 0; i < len; i++) {
+		ptrdiff_t offset = ltype->elems_offset + i * elem_size;
+		gu_dump(ltype->elem_type, &up[offset], ctx);
+	}
+	gu_yaml_end(ctx->yaml);
+}
+
+static void
+gu_dump_variant(GuDumpFn* dumper, GuType* type, const void* p,
+		GuDump* ctx)
+{
+	(void) dumper;
+	GuVariantType* vtype = gu_type_cast(type, GuVariant);
+	const GuVariant* vp = p;
+	int tag = gu_variant_tag(*vp);
+	for (int i = 0; i < vtype->ctors.len; i++) {
+		GuConstructor* ctor = &vtype->ctors.elems[i];
+		if (ctor->c_tag == tag) {
+			gu_yaml_begin_mapping(ctx->yaml);
+			gu_dump_str_scalar(ctx, ctor->c_name);
+			void* data = gu_variant_data(*vp);
+			gu_dump(ctor->type, data, ctx);
+			gu_yaml_end(ctx->yaml);
+			return;
+		}
+	}
+	gu_assert(false);
+}
+
+
+static void
+gu_dump_enum(GuDumpFn* dumper, GuType* type, const void* p,
+	     GuDump* ctx)
+{
+	(void) dumper;
+	GuEnumType* etype = gu_type_cast(type, enum);
+	GuEnumConstant* cp = gu_enum_value(etype, p);
+	gu_assert(cp != NULL);
+	gu_dump_str_scalar(ctx, cp->name);
+}
+
+static void
+gu_dump_seq(GuDumpFn* dumper, GuType* type, const void* p,
+	    GuDump* ctx)
+{
+	(void) dumper;
+	GuSeqType* dtype = gu_type_cast(type, GuSeq);
+	size_t elem_size = gu_type_size(dtype->elem_type);
+	const GuSeq* seqp = p;
+	GuSeq seq = *seqp;
+	if (gu_seq_is_null(seq)) {
+		gu_dump_null(ctx);
+		return;
+	}
+	size_t len = gu_seq_length(seq);
+	const uint8_t* data = gu_seq_data(seq);
+	gu_yaml_begin_sequence(ctx->yaml);
+	for (size_t i = 0; i < len; i++) {
+		const void* elemp = &data[i * elem_size];
+		gu_dump(dtype->elem_type, elemp, ctx);
+	}
+	gu_yaml_end(ctx->yaml);
+}
+
+
+GuTypeTable
+gu_dump_table = GU_TYPETABLE(
+	GU_SLIST_0,
+	{ gu_kind(int), gu_fn(gu_dump_int) },
+	{ gu_kind(uint16_t), gu_fn(gu_dump_uint16) },
+	{ gu_kind(size_t), gu_fn(gu_dump_size) },
+	{ gu_kind(GuStr), gu_fn(gu_dump_str) },
+	{ gu_kind(GuString), gu_fn(gu_dump_string) },
+	{ gu_kind(struct), gu_fn(gu_dump_struct) },
+	{ gu_kind(pointer), gu_fn(gu_dump_pointer) },
+	{ gu_kind(GuMap), gu_fn(gu_dump_map) },
+	{ gu_kind(alias), gu_fn(gu_dump_alias) },
+	{ gu_kind(reference), gu_fn(gu_dump_reference) },
+	{ gu_kind(referenced), gu_fn(gu_dump_referenced) },
+	{ gu_kind(shared), gu_fn(gu_dump_shared) },
+	{ gu_kind(GuList), gu_fn(gu_dump_list) },
+	{ gu_kind(GuSeq), gu_fn(gu_dump_seq) },
+	{ gu_kind(GuLength), gu_fn(gu_dump_length) },
+	{ gu_kind(GuVariant), gu_fn(gu_dump_variant) },
+	{ gu_kind(double), gu_fn(gu_dump_double) },
+	{ gu_kind(enum), gu_fn(gu_dump_enum) },
+	);
diff --git a/src/runtime/c/gu/dump.h b/src/runtime/c/gu/dump.h
new file mode 100644
index 000000000..7d6f10a77
--- /dev/null
+++ b/src/runtime/c/gu/dump.h
@@ -0,0 +1,34 @@
+#ifndef GU_DUMP_H_
+#define GU_DUMP_H_
+
+#include <gu/defs.h>
+#include <gu/yaml.h>
+#include <gu/type.h>
+#include <gu/map.h>
+
+typedef struct GuDump GuDump;
+
+struct GuDump {
+	GuPool* pool;
+	GuYaml* yaml;
+	GuMap* data;
+	GuTypeMap* dumpers;
+	bool print_address;
+};
+
+typedef void (*GuDumpFn)(GuFn* self, GuType* type, const void* value, GuDump* ctx);
+
+GuDump*
+gu_new_dump(GuWriter* wtr, GuTypeTable* dumpers, GuExn* err, GuPool* pool);
+
+void
+gu_dump(GuType* type, const void* value, GuDump* ctx);
+
+void
+gu_dump_stderr(GuType* type, const void* value, GuExn* err);
+
+extern GuTypeTable
+gu_dump_table;
+
+
+#endif // GU_DUMP_H_
diff --git a/src/runtime/c/gu/enum.c b/src/runtime/c/gu/enum.c
new file mode 100644
index 000000000..fa8595a55
--- /dev/null
+++ b/src/runtime/c/gu/enum.c
@@ -0,0 +1,7 @@
+#include <gu/enum.h>
+
+void
+gu_enum_next(GuEnum* en, void* to, GuPool* pool)
+{
+	en->next(en, to, pool);
+}
diff --git a/src/runtime/c/gu/enum.h b/src/runtime/c/gu/enum.h
new file mode 100644
index 000000000..88cd5ba6a
--- /dev/null
+++ b/src/runtime/c/gu/enum.h
@@ -0,0 +1,35 @@
+#ifndef GU_ENUM_H_
+#define GU_ENUM_H_
+
+#include <gu/mem.h>
+
+typedef struct GuEnum GuEnum;
+
+struct GuEnum {
+	void (*next)(GuEnum* self, void* to, GuPool* pool);
+};
+
+void
+gu_enum_next(GuEnum* en, void* to, GuPool* pool);
+
+#ifdef GU_GNUC
+
+#define gu_next(ENUM, T, POOL)						\
+	({								\
+		T gu_next_tmp_;						\
+		gu_enum_next((ENUM), &gu_next_tmp_, (POOL));		\
+		gu_next_tmp_;						\
+	})
+#else
+static inline void*
+gu_enum_next_(GuEnum* en, void* to, GuPool* pool)
+{
+	gu_enum_next(en, to, pool);
+	return to;
+}
+#define gu_next(ENUM, T, POOL)			\
+	(*(T*)gu_enum_next_((ENUM), &(T){0}, (POOL)))
+
+#endif
+
+#endif /* GU_ENUM_H_ */
diff --git a/src/runtime/c/gu/exn.c b/src/runtime/c/gu/exn.c
new file mode 100644
index 000000000..7bcfeb088
--- /dev/null
+++ b/src/runtime/c/gu/exn.c
@@ -0,0 +1,72 @@
+#include <gu/exn.h>
+#include <gu/assert.h>
+
+
+GuExn*
+gu_new_exn(GuExn* parent, GuKind* catch, GuPool* pool)
+{
+	return gu_new_s(pool, GuExn,
+			.state = GU_EXN_OK,
+			.parent = parent,
+			.catch = catch,
+			.caught = NULL,
+			.data.pool = pool,
+			.data.data = NULL);
+}
+
+void
+gu_exn_block(GuExn* err)
+{
+	if (err && err->state == GU_EXN_RAISED) {
+		err->state = GU_EXN_BLOCKED;
+	}
+}
+
+void
+gu_exn_unblock(GuExn* err)
+{
+	if (err && err->state == GU_EXN_BLOCKED) {
+		err->state = GU_EXN_RAISED;
+	}
+}
+
+GuExnData*
+gu_exn_raise_debug_(GuExn* base, GuType* type, 
+		      const char* filename, const char* func, int lineno)
+{
+	gu_require(type);
+
+	// TODO: log the error, once there's a system for dumping
+	// error objects.
+
+	GuExn* err = base;
+	
+	while (err && !(err->catch && gu_type_has_kind(type, err->catch))) {
+		err->state = GU_EXN_RAISED;
+		err = err->parent;
+	}
+	if (!err) {
+		gu_abort_(GU_ASSERT_ASSERTION, filename, func, lineno,
+			  "Unexpected error raised");
+	}
+	GuExnState old_state = err->state;
+	err->state = GU_EXN_RAISED;
+	if (old_state == GU_EXN_OK) {
+		err->caught = type;
+		if (err->data.pool) {
+			return &err->data;
+		}
+	}
+	// Exceptian had already been raised, possibly blocked, or no
+	// exception value is required.
+	return NULL;
+}
+
+GuExnData*
+gu_exn_raise_(GuExn* base, GuType* type)
+{
+	return gu_exn_raise_debug_(base, type, NULL, NULL, -1);
+}
+
+
+GU_DEFINE_TYPE(GuErrno, signed, _);
diff --git a/src/runtime/c/gu/exn.h b/src/runtime/c/gu/exn.h
new file mode 100644
index 000000000..66ca107e3
--- /dev/null
+++ b/src/runtime/c/gu/exn.h
@@ -0,0 +1,195 @@
+#ifndef GU_EXN_H_
+#define GU_EXN_H_
+
+#include <gu/mem.h>
+#include <gu/type.h>
+
+/** @file
+ *
+ * @defgroup GuExn Exceptions
+ * Defined in <gu/exn.h>.
+ * @{
+ */
+
+/// An exception frame.
+typedef struct GuExn GuExn;
+
+/// @private
+typedef enum {
+	GU_EXN_RAISED,
+	GU_EXN_OK,
+	GU_EXN_BLOCKED
+} GuExnState;
+
+typedef struct GuExnData GuExnData;
+
+/// A structure for storing exception values.
+struct GuExnData
+/**
+ * When an exception is raised, if there is an associated value, it
+ * must be allocated from a pool that still exists when control
+ * returns to the handler of that exception. This structure is used to
+ * communicate the exception from the raiser to the handler: the
+ * handler sets #pool when setting up the exception frame, and the
+ * raiser uses that pool to allocate the value and stores that in
+ * #data. When control returns to the handler, it reads the value from
+ * there.
+ */
+{
+	
+	/// The pool that the exception value should be allocated from.
+	GuPool* const pool;
+
+	/// The exception value.
+	const void* data;
+};
+
+struct GuExn {
+	/// @privatesection
+	GuExnState state;
+	GuExn* parent;
+	GuKind* catch;
+	GuType* caught;
+	GuExnData data;
+};
+
+
+/// @name Creating exception frames
+//@{
+
+
+/// Allocate a new local exception frame.
+#define gu_exn(parent_, catch_, pool_) &(GuExn){	\
+	.state = GU_EXN_OK,	\
+	.parent = parent_,	\
+	.catch = gu_kind(catch_),	\
+	.caught = NULL,	\
+	.data.pool = pool_,		\
+	.data.data = NULL \
+}
+
+
+/// Allocate a new exception frame.
+GuExn*
+gu_new_exn(GuExn* parent, GuKind* catch_kind, GuPool* pool);
+
+
+
+static inline bool
+gu_exn_is_raised(GuExn* err) {
+	return err && (err->state == GU_EXN_RAISED);
+}
+
+static inline void
+gu_exn_clear(GuExn* err) {
+	err->caught = NULL;
+	err->state = GU_EXN_OK;
+}
+
+
+
+GuType*
+gu_exn_caught(GuExn* err);
+
+const void*
+gu_exn_caught_data(GuExn* err);
+
+/// Temporarily block a raised exception.
+void
+gu_exn_block(GuExn* err);
+
+/// Show again a blocked exception.
+void
+gu_exn_unblock(GuExn* err);
+
+//@private
+GuExnData*
+gu_exn_raise_(GuExn* err, GuType* type);
+
+//@private
+GuExnData*
+gu_exn_raise_debug_(GuExn* err, GuType* type,
+		      const char* filename, const char* func, int lineno);
+
+#ifdef NDEBUG
+#define gu_exn_raise(err_, type_)	\
+	gu_exn_raise_(err_, type_)
+#else
+#define gu_exn_raise(err_, type_)	\
+	gu_exn_raise_debug_(err_, type_, \
+			      __FILE__, __func__, __LINE__)
+#endif
+
+/// Raise an exception.
+#define gu_raise(exn, T)		\
+	gu_exn_raise(exn, gu_type(T))
+/**< 
+ * @param exn The current exception frame.
+ *
+ * @param T   The C type of the exception to raise.
+ *
+ * @return    A #GuExnData object that can be used to store the exception value, or
+ * \c NULL if no value is required.
+ * 
+ * @note The associated #GuType object for type \p T must be visible.
+ */
+
+#define gu_raise_new(error_, t_, pool_, expr_)				\
+	GU_BEGIN							\
+	GuExnData* gu_raise_err_ = gu_raise(error_, t_);		\
+	if (gu_raise_err_) {						\
+		GuPool* pool_ = gu_raise_err_->pool;			\
+		gu_raise_err_->data = expr_;				\
+	}								\
+	GU_END
+
+#define gu_raise_i(error_, t_, ...) \
+	gu_raise_new(error_, t_, gu_raise_pool_, gu_new_i(gu_raise_pool_, t_, __VA_ARGS__))
+
+
+/// Check the status of the current exception frame
+static inline bool
+gu_ok(GuExn* exn) {
+	return !GU_UNLIKELY(gu_exn_is_raised(exn));
+}
+/**<
+ * @return \c false if an exception has been raised in the frame \p exn
+ * and it has not been blocked, \c true otherwise.
+ */
+
+
+/// Return from current function if an exception has been raised.
+#define gu_return_on_exn(exn_, retval_)		\
+	GU_BEGIN					\
+	if (gu_exn_is_raised(exn_)) return retval_;	\
+	GU_END
+/**<
+ * @showinitializer
+ */
+
+
+#include <errno.h>
+
+typedef int GuErrno;
+
+extern GU_DECLARE_TYPE(GuErrno, signed);
+
+
+
+#define gu_raise_errno(error_) \
+	gu_raise_i(error_, GuErrno, errno)
+
+#if 0
+
+typedef void (*GuExnPrintFn)(GuFn* clo, void* err, FILE* out);
+
+extern GuTypeTable gu_exn_default_printer;
+
+void
+gu_exn_print(GuExn* err, FILE* out, GuTypeMap printer_map);
+
+#endif
+
+/** @} */
+
+#endif // GU_EXN_H_
diff --git a/src/runtime/c/gu/file.c b/src/runtime/c/gu/file.c
new file mode 100644
index 000000000..ed1956537
--- /dev/null
+++ b/src/runtime/c/gu/file.c
@@ -0,0 +1,73 @@
+#include <gu/file.h>
+
+typedef struct GuFileOutStream GuFileOutStream;
+
+struct GuFileOutStream {
+	GuOutStream stream;
+	FILE* file;
+};
+
+static size_t
+gu_file_output(GuOutStream* stream, const uint8_t* buf, size_t len, GuExn* err)
+{
+	GuFileOutStream* fos = gu_container(stream, GuFileOutStream, stream);
+	errno = 0;
+	size_t wrote = fwrite(buf, 1, len, fos->file);
+	if (wrote < len) {
+		if (ferror(fos->file)) {
+			gu_raise_errno(err);
+		}
+	}
+	return wrote;
+}
+
+static void
+gu_file_flush(GuOutStream* stream, GuExn* err)
+{
+	GuFileOutStream* fos = gu_container(stream, GuFileOutStream, stream);
+	errno = 0;
+	if (fflush(fos->file) != 0) {
+		gu_raise_errno(err);
+	}
+}
+
+GuOut*
+gu_file_out(FILE* file, GuPool* pool)
+{
+	GuFileOutStream* fos = gu_new_i(pool, GuFileOutStream,
+					.stream.output = gu_file_output,
+					.stream.flush = gu_file_flush,
+					.file = file);
+	return gu_new_out(&fos->stream, pool);
+}
+
+
+typedef struct GuFileInStream GuFileInStream;
+
+struct GuFileInStream {
+	GuInStream stream;
+	FILE* file;
+};
+
+static size_t 
+gu_file_input(GuInStream* stream, uint8_t* buf, size_t sz, GuExn* err)
+{
+	GuFileInStream* fis = gu_container(stream, GuFileInStream, stream);
+	errno = 0;
+	size_t got = fread(buf, 1, sz, fis->file);
+	if (got == 0) {
+		if (ferror(fis->file)) {
+			gu_raise_errno(err);
+		}
+	}
+	return got;
+}
+
+GuIn*
+gu_file_in(FILE* file, GuPool* pool)
+{
+	GuFileInStream* fis = gu_new_s(pool, GuFileInStream,
+				       .stream.input = gu_file_input,
+				       .file = file);
+	return gu_new_in(&fis->stream, pool);
+}
diff --git a/src/runtime/c/gu/file.h b/src/runtime/c/gu/file.h
new file mode 100644
index 000000000..1bb3fb00a
--- /dev/null
+++ b/src/runtime/c/gu/file.h
@@ -0,0 +1,14 @@
+#ifndef GU_FILE_H_
+#define GU_FILE_H_
+
+#include <gu/in.h>
+#include <gu/out.h>
+#include <stdio.h>
+
+GuOut*
+gu_file_out(FILE* file, GuPool* pool);
+
+GuIn* 
+gu_file_in(FILE* file, GuPool* pool);
+
+#endif // GU_FILE_H_
diff --git a/src/runtime/c/gu/fun.c b/src/runtime/c/gu/fun.c
new file mode 100644
index 000000000..ca777c490
--- /dev/null
+++ b/src/runtime/c/gu/fun.c
@@ -0,0 +1 @@
+#include <gu/fun.h>
diff --git a/src/runtime/c/gu/fun.h b/src/runtime/c/gu/fun.h
new file mode 100644
index 000000000..0004e9923
--- /dev/null
+++ b/src/runtime/c/gu/fun.h
@@ -0,0 +1,65 @@
+#ifndef GU_FUN_H_
+#define GU_FUN_H_
+
+#include <gu/defs.h>
+
+typedef void (*GuFn)();
+typedef void (*GuFn0)(GuFn* clo);
+typedef void (*GuFn1)(GuFn* clo, void* arg1);
+typedef void (*GuFn2)(GuFn* clo, void* arg1, void* arg2);
+
+#define gu_fn(fn_) (&(GuFn){ fn_ })
+
+static inline void
+gu_apply0(GuFn* fn) {
+	(*fn)(fn);
+}
+
+static inline void
+gu_apply1(GuFn* fn, void* arg1) {
+	(*fn)(fn, arg1);
+}
+
+static inline void
+gu_apply2(GuFn* fn, void* arg1, void* arg2) {
+	(*fn)(fn, arg1, arg2);
+}
+
+#define gu_apply(fn_, ...)			\
+	((fn_)->fn((fn_), __VA_ARGS__))
+
+typedef struct GuClo0 GuClo0;
+
+struct GuClo0 {
+	GuFn fn;
+};
+
+typedef struct GuClo1 GuClo1;
+
+struct GuClo1 {
+	GuFn fn;
+	void *env1;
+};
+
+typedef struct GuClo2 GuClo2;
+struct GuClo2 {
+	GuFn fn;
+	void *env1;
+	void *env2;
+};
+
+typedef struct GuClo3 GuClo3;
+struct GuClo3 {
+	GuFn fn;
+	void *env1;
+	void *env2;
+	void *env3;
+};
+
+typedef const struct GuEquality GuEquality;
+
+struct GuEquality {
+	bool (*is_equal)(GuEquality* self, const void* a, const void* b);
+};
+
+#endif // GU_FUN_H_
diff --git a/src/runtime/c/gu/hash.c b/src/runtime/c/gu/hash.c
new file mode 100644
index 000000000..1666263e6
--- /dev/null
+++ b/src/runtime/c/gu/hash.c
@@ -0,0 +1,77 @@
+#include <gu/hash.h>
+
+GuHash
+gu_hash_bytes(GuHash h, const uint8_t* buf, size_t len)
+{
+	for (size_t n = 0; n < len; n++) {
+		h = gu_hash_byte(h, buf[n]);
+	}
+	return h;
+}
+
+static bool
+gu_int_eq_fn(GuEquality* self, const void* p1, const void* p2)
+{
+	(void) self;
+	const int* ip1 = p1;
+	const int* ip2 = p2;
+	return *ip1 == *ip2;
+}
+
+static GuHash
+gu_int_hash_fn(GuHasher* self, const void* p)
+{
+	(void) self;
+	return (GuHash) *(const int*) p;
+}
+
+GuHasher gu_int_hasher[1] = {
+	{
+		{ gu_int_eq_fn },
+		gu_int_hash_fn
+	}
+};
+
+static bool
+gu_addr_eq_fn(GuEquality* self, const void* p1, const void* p2)
+{
+	(void) self;
+	return (p1 == p2);
+}
+
+static GuHash
+gu_addr_hash_fn(GuHasher* self, const void* p)
+{
+	(void) self;
+	return (GuHash) (uintptr_t) p;
+}
+
+GuHasher gu_addr_hasher[1] = {
+	{
+		{ gu_addr_eq_fn },
+		gu_addr_hash_fn
+	}
+};
+
+static bool
+gu_word_eq_fn(GuEquality* self, const void* p1, const void* p2)
+{
+	(void) self;
+	const GuWord* wp1 = p1;
+	const GuWord* wp2 = p2;
+	return (*wp1 == *wp2);
+}
+
+static GuHash
+gu_word_hash_fn(GuHasher* self, const void* p)
+{
+	(void) self;
+	return (GuHash) (uintptr_t) p;
+}
+
+GuHasher gu_word_hasher[1] = {
+	{
+		{ gu_word_eq_fn },
+		gu_word_hash_fn
+	}
+};
diff --git a/src/runtime/c/gu/hash.h b/src/runtime/c/gu/hash.h
new file mode 100644
index 000000000..e16c2f454
--- /dev/null
+++ b/src/runtime/c/gu/hash.h
@@ -0,0 +1,40 @@
+#ifndef GU_HASH_H_
+#define GU_HASH_H_
+
+#include <gu/fun.h>
+
+typedef GuWord GuHash;
+
+static inline GuHash
+gu_hash_ptr(void* ptr)
+{
+	return (GuHash) ptr;
+}
+
+
+static inline GuHash
+gu_hash_byte(GuHash h, uint8_t u)
+{
+	// Paul Larson's simple byte hash
+	return h * 101 + u;
+}
+
+
+GuHash
+gu_hash_bytes(GuHash h, const uint8_t* buf, size_t len);
+
+typedef const struct GuHasher GuHasher;
+
+struct GuHasher {
+	GuEquality eq;
+	GuHash (*hash)(GuHasher* self, const void* p);
+};
+
+
+extern GuHasher gu_int_hasher[1];
+
+extern GuHasher gu_addr_hasher[1];
+
+extern GuHasher gu_word_hasher[1];
+
+#endif // GU_HASH_H_
diff --git a/src/runtime/c/gu/in.c b/src/runtime/c/gu/in.c
new file mode 100644
index 000000000..4238475f8
--- /dev/null
+++ b/src/runtime/c/gu/in.c
@@ -0,0 +1,421 @@
+#include <gu/in.h>
+#include <gu/bits.h>
+#include <math.h>
+
+GU_DEFINE_TYPE(GuEOF, abstract, _);
+
+
+static bool
+gu_in_is_buffering(GuIn* in)
+{
+	return (in->buf_end != NULL);
+}
+
+static void
+gu_in_end_buffering(GuIn* in, GuExn* err)
+{
+	if (!gu_in_is_buffering(in)) {
+		return;
+	}
+	if (in->stream->end_buffer) {
+		size_t len = ((ptrdiff_t) in->buf_size) + in->buf_curr;
+		in->stream->end_buffer(in->stream, len, err);
+	}
+	in->buf_curr = 0;
+	in->buf_size = 0;
+	in->buf_end = NULL;
+}
+
+static bool
+gu_in_begin_buffering(GuIn* in, GuExn* err)
+{
+	if (gu_in_is_buffering(in)) {
+		if (in->buf_curr < 0) {
+			return true;
+		} else {
+			gu_in_end_buffering(in, err);
+			if (!gu_ok(err)) return false;
+		}
+	}
+	if (!in->stream->begin_buffer) {
+		return false;
+	}
+	size_t sz = 0;
+	const uint8_t* new_buf = 
+		in->stream->begin_buffer(in->stream, &sz, err);
+	if (new_buf) {
+		in->buf_end = &new_buf[sz];
+		in->buf_curr = -(ptrdiff_t) sz;
+		in->buf_size = sz;
+		return true;
+	}
+	return false;
+}
+
+static size_t
+gu_in_input(GuIn* in, uint8_t* dst, size_t sz, GuExn* err)
+{
+	if (sz == 0) {
+		return 0;
+	}
+	gu_in_end_buffering(in, err);
+	if (!gu_ok(err)) {
+		return 0;
+	}
+	GuInStream* stream = in->stream;
+	if (stream->input) {
+		return stream->input(stream, dst, sz, err);
+	}
+	gu_raise(err, GuEOF);
+	return 0;
+}
+
+size_t
+gu_in_some(GuIn* in, uint8_t* dst, size_t sz, GuExn* err)
+{
+	gu_require(sz <= PTRDIFF_MAX);
+	if (!gu_in_begin_buffering(in, err)) {
+		if (!gu_ok(err)) return 0; 
+		return gu_in_input(in, dst, sz, err);
+	}
+	size_t real_sz = GU_MIN(sz, (size_t)(-in->buf_curr));
+	memcpy(dst, &in->buf_end[in->buf_curr], real_sz);
+	in->buf_curr += real_sz;
+	return real_sz;
+}
+
+void
+gu_in_bytes_(GuIn* in, uint8_t* dst, size_t sz, GuExn* err)
+{
+	size_t avail_sz = GU_MIN(sz, (size_t)(-in->buf_curr));
+	memcpy(dst, &in->buf_end[in->buf_curr], avail_sz);
+	in->buf_curr += avail_sz;
+	if (avail_sz < sz) {
+		gu_in_input(in, &dst[avail_sz], sz - avail_sz, err);
+	}
+}
+
+const uint8_t*
+gu_in_begin_span(GuIn* in, size_t *sz_out, GuExn* err)
+{
+	if (!gu_in_begin_buffering(in, err)) {
+		return NULL;
+	}
+	*sz_out = (size_t) -in->buf_curr;
+	return &in->buf_end[in->buf_curr];
+}
+
+void
+gu_in_end_span(GuIn* in, size_t consumed)
+{
+	gu_require(consumed <= (size_t) -in->buf_curr);
+	in->buf_curr += (ptrdiff_t) consumed;
+}
+
+uint8_t 
+gu_in_u8_(GuIn* in, GuExn* err)
+{
+	if (gu_in_begin_buffering(in, err) && in->buf_curr < 0) {
+		return in->buf_end[in->buf_curr++];
+	}
+	uint8_t u = 0;
+	size_t r = gu_in_input(in, &u, 1, err);
+	if (r < 1) {
+		gu_raise(err, GuEOF);
+		return 0;
+	}
+	return u;
+}
+
+static uint64_t
+gu_in_be(GuIn* in, GuExn* err, int n)
+{
+	uint8_t buf[8];
+	gu_in_bytes(in, buf, n, err);
+	uint64_t u = 0;
+	for (int i = 0; i < n; i++) {
+		u = u << 8 | buf[i];
+	}
+	return u;
+}
+
+static uint64_t
+gu_in_le(GuIn* in, GuExn* err, int n)
+{
+	uint8_t buf[8];
+	gu_in_bytes(in, buf, n, err);
+	uint64_t u = 0;
+	for (int i = 0; i < n; i++) {
+		u = u << 8 | buf[i];
+	}
+	return u;
+}
+
+int8_t 
+gu_in_s8(GuIn* in, GuExn* err)
+{
+	return gu_decode_2c8(gu_in_u8(in, err), err);
+}
+
+
+uint16_t
+gu_in_u16le(GuIn* in, GuExn* err)
+{
+	return gu_in_le(in, err, 2);
+}
+
+int16_t 
+gu_in_s16le(GuIn* in, GuExn* err)
+{
+	return gu_decode_2c16(gu_in_u16le(in, err), err);
+}
+
+uint16_t
+gu_in_u16be(GuIn* in, GuExn* err)
+{
+	return gu_in_be(in, err, 2);
+}
+
+int16_t 
+gu_in_s16be(GuIn* in, GuExn* err)
+{
+	return gu_decode_2c16(gu_in_u16be(in, err), err);
+}
+
+
+uint32_t
+gu_in_u32le(GuIn* in, GuExn* err)
+{
+	return gu_in_le(in, err, 4);
+}
+
+int32_t 
+gu_in_s32le(GuIn* in, GuExn* err)
+{
+	return gu_decode_2c32(gu_in_u32le(in, err), err);
+}
+
+uint32_t
+gu_in_u32be(GuIn* in, GuExn* err)
+{
+	return gu_in_be(in, err, 4);
+}
+
+int32_t 
+gu_in_s32be(GuIn* in, GuExn* err)
+{
+	return gu_decode_2c32(gu_in_u32be(in, err), err);
+}
+
+
+uint64_t
+gu_in_u64le(GuIn* in, GuExn* err)
+{
+	return gu_in_le(in, err, 8);
+}
+
+int64_t 
+gu_in_s64le(GuIn* in, GuExn* err)
+{
+	return gu_decode_2c64(gu_in_u64le(in, err), err);
+}
+
+uint64_t
+gu_in_u64be(GuIn* in, GuExn* err)
+{
+	return gu_in_be(in, err, 8);
+}
+
+int64_t 
+gu_in_s64be(GuIn* in, GuExn* err)
+{
+	return gu_decode_2c64(gu_in_u64be(in, err), err);
+}
+
+double
+gu_in_f64le(GuIn* in, GuExn* err)
+{
+	return gu_decode_double(gu_in_u64le(in, err));
+}
+
+double
+gu_in_f64be(GuIn* in, GuExn* err)
+{
+	return gu_decode_double(gu_in_u64le(in, err));
+}
+
+
+static void
+gu_in_fini(GuFinalizer* fin)
+{
+	GuIn* in = gu_container(fin, GuIn, fini);
+	GuPool* pool = gu_local_pool();
+	GuExn* err = gu_exn(NULL, type, pool);
+	gu_in_end_buffering(in, err);
+	gu_pool_free(pool);
+}
+
+GuIn
+gu_init_in(GuInStream* stream)
+{
+	return (GuIn) {
+		.buf_end = NULL,
+		.buf_curr = 0,
+		.buf_size = 0,
+		.stream = stream,
+		.fini.fn = gu_in_fini
+	};
+}
+
+GuIn*
+gu_new_in(GuInStream* stream, GuPool* pool)
+{
+	GuIn* in = gu_new(GuIn, pool);
+	*in = gu_init_in(stream);
+	return in;
+}
+
+
+typedef struct GuProxyInStream GuProxyInStream;
+
+struct GuProxyInStream {
+	GuInStream stream;
+	GuIn* real_in;
+};
+
+static const uint8_t*
+gu_proxy_in_begin_buffer(GuInStream* self, size_t* sz_out, GuExn* err)
+{
+	GuProxyInStream* pis = gu_container(self, GuProxyInStream, stream);
+	return gu_in_begin_span(pis->real_in, sz_out, err);
+}
+
+static void
+gu_proxy_in_end_buffer(GuInStream* self, size_t sz, GuExn* err)
+{
+	GuProxyInStream* pis = gu_container(self, GuProxyInStream, stream);
+	gu_in_end_span(pis->real_in, sz);
+}
+
+static size_t
+gu_proxy_in_input(GuInStream* self, uint8_t* dst, size_t sz, GuExn* err)
+{
+	GuProxyInStream* pis = gu_container(self, GuProxyInStream, stream);
+	return gu_in_some(pis->real_in, dst, sz, err);
+}
+
+GuInStream*
+gu_in_proxy_stream(GuIn* in, GuPool* pool)
+{
+	return &gu_new_s(
+		pool, GuProxyInStream,
+		.stream.begin_buffer = gu_proxy_in_begin_buffer,
+		.stream.end_buffer = gu_proxy_in_end_buffer,
+		.stream.input = gu_proxy_in_input,
+		.real_in = in)->stream;
+}
+
+enum {
+	GU_BUFFERED_IN_BUF_SIZE = 4096
+};
+
+typedef struct GuBufferedInStream GuBufferedInStream;
+
+struct GuBufferedInStream {
+	GuInStream stream;
+	size_t alloc;
+	size_t have;
+	size_t curr;
+	GuIn* in;
+	uint8_t buf[];
+};
+
+static const uint8_t*
+gu_buffered_in_begin_buffer(GuInStream* self, size_t* sz_out, GuExn* err)
+{
+	GuBufferedInStream* bis = 
+		gu_container(self, GuBufferedInStream, stream);
+	if (bis->curr == bis->have) {
+		bis->curr = 0;
+		bis->have = gu_in_some(bis->in, bis->buf, bis->alloc, err);
+		if (!gu_ok(err)) return NULL;
+	}
+	*sz_out = bis->have - bis->curr;
+	return &bis->buf[bis->curr];
+}
+
+static void
+gu_buffered_in_end_buffer(GuInStream* self, size_t consumed, GuExn* err)
+{
+	GuBufferedInStream* bis = 
+		gu_container(self, GuBufferedInStream, stream);
+	gu_require(consumed < bis->have - bis->curr);
+	bis->curr += consumed;
+}
+
+static size_t
+gu_buffered_in_input(GuInStream* self, uint8_t* dst, size_t sz, GuExn* err)
+{
+	GuBufferedInStream* bis = 
+		gu_container(self, GuBufferedInStream, stream);
+	return gu_in_some(bis->in, dst, sz, err);
+}
+
+GuIn*
+gu_buffered_in(GuIn* in, size_t buf_sz, GuPool* pool)
+{
+	GuBufferedInStream* bis = gu_new_flex(pool, GuBufferedInStream,
+					      buf, buf_sz);
+	bis->stream = (GuInStream) {
+		.begin_buffer = gu_buffered_in_begin_buffer,
+		.end_buffer = gu_buffered_in_end_buffer,
+		.input = gu_buffered_in_input
+	};
+	bis->have = bis->curr = 0;
+	bis->alloc = buf_sz;
+	return gu_new_in(&bis->stream, pool);
+}
+
+typedef struct GuDataIn GuDataIn;
+
+struct GuDataIn {
+	GuInStream stream; 
+	const uint8_t* data;
+	size_t sz;
+};
+
+static const uint8_t*
+gu_data_in_begin_buffer(GuInStream* self, size_t* sz_out, GuExn* err)
+{
+	(void) err;
+	GuDataIn* di = gu_container(self, GuDataIn, stream);
+	const uint8_t* buf = di->data;
+	if (buf) {
+		*sz_out = di->sz;
+		di->data = NULL;
+		di->sz = 0;
+	}
+	return buf;
+}
+
+GuIn*
+gu_data_in(const uint8_t* data, size_t sz, GuPool* pool)
+{
+	GuDataIn* di = gu_new_s(pool, GuDataIn,
+				.stream.begin_buffer = gu_data_in_begin_buffer,
+				.data = data,
+				.sz = sz);
+	return gu_new_in(&di->stream, pool);
+}
+
+extern inline uint8_t 
+gu_in_u8(GuIn* restrict in, GuExn* err);
+
+extern inline void
+gu_in_bytes(GuIn* in, uint8_t* buf, size_t sz, GuExn* err);
+
+extern inline int
+gu_in_peek_u8(GuIn* restrict in);
+
+extern inline void
+gu_in_consume(GuIn* restrict in, size_t sz);
diff --git a/src/runtime/c/gu/in.h b/src/runtime/c/gu/in.h
new file mode 100644
index 000000000..c85a6581b
--- /dev/null
+++ b/src/runtime/c/gu/in.h
@@ -0,0 +1,146 @@
+#ifndef GU_IN_H_
+#define GU_IN_H_
+
+#include <gu/defs.h>
+#include <gu/exn.h>
+#include <gu/assert.h>
+
+typedef struct GuInStream GuInStream;
+
+struct GuInStream {
+	const uint8_t* (*begin_buffer)(GuInStream* self, size_t* sz_out, 
+				       GuExn* err);
+	void (*end_buffer)(GuInStream* self, size_t consumed, GuExn* err);
+	size_t (*input)(GuInStream* self, uint8_t* buf, size_t max_sz, 
+			GuExn* err);
+};
+
+typedef struct GuIn GuIn;
+
+struct GuIn {
+	const uint8_t* restrict buf_end;
+	ptrdiff_t buf_curr;
+	size_t buf_size;
+	GuInStream* stream;
+	GuFinalizer fini;
+};
+
+
+GuIn
+gu_init_in(GuInStream* stream);
+
+GuIn*
+gu_new_in(GuInStream* stream, GuPool* pool);
+
+GuInStream*
+gu_in_proxy_stream(GuIn* in, GuPool* pool);
+
+const uint8_t*
+gu_in_begin_span(GuIn* in, size_t *sz_out, GuExn* err);
+
+void
+gu_in_end_span(GuIn* in, size_t consumed);
+
+size_t
+gu_in_some(GuIn* in, uint8_t* buf, size_t max_len, GuExn* err);
+
+inline void
+gu_in_bytes(GuIn* in, uint8_t* buf, size_t sz, GuExn* err)
+{
+	gu_require(sz < PTRDIFF_MAX);
+	ptrdiff_t curr = in->buf_curr;
+	ptrdiff_t new_curr = curr + (ptrdiff_t) sz;
+	if (GU_UNLIKELY(new_curr > 0)) {
+		extern void gu_in_bytes_(GuIn* in, uint8_t* buf, size_t sz, 
+					 GuExn* err);
+		gu_in_bytes_(in, buf, sz, err);
+		return;
+	}
+	memcpy(buf, &in->buf_end[curr], sz);
+	in->buf_curr = new_curr;
+}
+
+inline int
+gu_in_peek_u8(GuIn* restrict in)
+{
+	if (GU_UNLIKELY(in->buf_curr == 0)) {
+		return -1;
+	}
+	return in->buf_end[in->buf_curr];
+}
+
+inline void
+gu_in_consume(GuIn* restrict in, size_t sz)
+{
+	gu_require((ptrdiff_t) sz + in->buf_curr <= 0);
+	in->buf_curr += sz;
+}
+
+
+inline uint8_t 
+gu_in_u8(GuIn* restrict in, GuExn* err)
+{
+	if (GU_UNLIKELY(in->buf_curr == 0)) {
+		extern uint8_t gu_in_u8_(GuIn* restrict in, GuExn* err);
+		return gu_in_u8_(in, err);
+	}
+	return in->buf_end[in->buf_curr++];
+}
+
+int8_t 
+gu_in_s8(GuIn* in, GuExn* err);
+
+uint16_t
+gu_in_u16le(GuIn* in, GuExn* err);
+
+uint16_t
+gu_in_u16be(GuIn* in, GuExn* err);
+
+int16_t
+gu_in_s16le(GuIn* in, GuExn* err);
+
+int16_t
+gu_in_s16be(GuIn* in, GuExn* err);
+
+uint32_t
+gu_in_u32le(GuIn* in, GuExn* err);
+
+uint32_t
+gu_in_u32be(GuIn* in, GuExn* err);
+
+int32_t
+gu_in_s32le(GuIn* in, GuExn* err);
+
+int32_t
+gu_in_s32be(GuIn* in, GuExn* err);
+
+uint64_t
+gu_in_u64le(GuIn* in, GuExn* err);
+
+uint64_t
+gu_in_u64be(GuIn* in, GuExn* err);
+
+int64_t
+gu_in_s64le(GuIn* in, GuExn* err);
+
+int64_t
+gu_in_s64be(GuIn* in, GuExn* err);
+
+double
+gu_in_f64le(GuIn* in, GuExn* err);
+
+double
+gu_in_f64be(GuIn* in, GuExn* err);
+
+GuIn*
+gu_buffered_in(GuIn* in, size_t sz, GuPool* pool);
+
+GuIn*
+gu_data_in(const uint8_t* buf, size_t size, GuPool* pool);
+
+
+extern GU_DECLARE_TYPE(GuEOF, abstract);
+
+#include <gu/type.h>
+
+#endif // GU_IN_H_
diff --git a/src/runtime/c/gu/intern.c b/src/runtime/c/gu/intern.c
new file mode 100644
index 000000000..35eaa1c5f
--- /dev/null
+++ b/src/runtime/c/gu/intern.c
@@ -0,0 +1,59 @@
+#include "intern.h"
+
+struct GuIntern {
+	GuPool* str_pool;
+	GuMap* map;
+};
+
+GuIntern*
+gu_new_intern(GuPool* str_pool, GuPool* pool)
+{
+	GuIntern* intern = gu_new(GuIntern, pool);
+	intern->str_pool = str_pool;
+	intern->map = gu_new_set(const char*, gu_str_hasher, pool);
+	return intern;
+}
+
+const char*
+gu_intern_str(GuIntern* intern, const char* cstr)
+{
+	const char* const* strp = gu_map_find_key(intern->map, &cstr);
+	if (strp) {
+		return *strp;
+	}
+	const char* str = gu_strdup(cstr, intern->str_pool);
+	gu_map_insert(intern->map, &str);
+	return str;
+}
+
+
+
+
+struct GuSymTable {
+	GuPool* sym_pool;
+	GuMap* map;
+};
+
+GuSymTable*
+gu_new_symtable(GuPool* sym_pool, GuPool* pool)
+{
+	GuSymTable* tab = gu_new(GuSymTable, pool);
+	tab->sym_pool = sym_pool;
+	tab->map = gu_new_set(GuSymbol, gu_string_hasher, pool);
+	return tab;
+}
+
+GuSymbol
+gu_symtable_intern(GuSymTable* tab, GuString string)
+{
+	if (gu_string_is_stable(string)) {
+		return string;
+	}
+	const GuSymbol* symp = gu_map_find_key(tab->map, &string);
+	if (symp) {
+		return *symp;
+	}
+	GuSymbol sym = gu_string_copy(string, tab->sym_pool);
+	gu_map_insert(tab->map, &sym);
+	return sym;
+}
diff --git a/src/runtime/c/gu/intern.h b/src/runtime/c/gu/intern.h
new file mode 100644
index 000000000..bf9e9b321
--- /dev/null
+++ b/src/runtime/c/gu/intern.h
@@ -0,0 +1,24 @@
+#ifndef GU_INTERN_H_
+#define GU_INTERN_H_
+
+#include <gu/map.h>
+#include <gu/str.h>
+#include <gu/string.h>
+
+typedef struct GuIntern GuIntern;
+
+GuIntern* gu_new_intern(GuPool* str_pool, GuPool* pool);
+const char* gu_intern_str(GuIntern* intern, const char* cstr);
+
+
+typedef struct GuSymTable GuSymTable;
+
+typedef GuString GuSymbol;
+
+GuSymTable*
+gu_new_symtable(GuPool* sym_pool, GuPool* pool);
+
+GuSymbol
+gu_symtable_intern(GuSymTable* symtab, GuString string);
+
+#endif /* GU_INTERN_H_ */
diff --git a/src/runtime/c/gu/list.c b/src/runtime/c/gu/list.c
new file mode 100644
index 000000000..d98a42e41
--- /dev/null
+++ b/src/runtime/c/gu/list.c
@@ -0,0 +1,59 @@
+/* 
+ * Copyright 2010 University of Helsinki.
+ *   
+ * This file is part of libgu.
+ * 
+ * Libgu is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ * 
+ * Libgu is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with libgu. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <gu/list.h>
+#include <gu/assert.h>
+#include <string.h>
+
+static const int gu_list_empty = 0;
+
+void* gu_list_alloc(GuPool* pool, size_t base_size, size_t elem_size, 
+		       int n_elems, size_t alignment)
+{
+	gu_assert(n_elems >= 0);
+	if (n_elems == 0) {
+		return (void*) &gu_list_empty;
+	}
+	// XXX: use gu_flex_size, use offset of elems
+	void* p = gu_malloc_aligned(pool, base_size + elem_size * n_elems,
+				    alignment);
+	*(int*) p = n_elems;
+	return p;
+}
+
+
+GU_DEFINE_KIND(GuList, abstract);
+
+// GU_DEFINE_TYPE(GuStrs, GuList, gu_type(GuStr));
+// GU_DEFINE_TYPE(GuStrsP, pointer, gu_type(GuStrs));
+
+void*
+gu_list_type_alloc(GuListType* ltype, int n_elems, GuPool* pool)
+{
+	return gu_list_alloc(pool, ltype->size, 
+			     gu_type_size(ltype->elem_type),
+			     n_elems, ltype->align);
+}
+
+void*
+gu_list_type_index(GuListType* ltype, void* list, int i)
+{
+	uint8_t* p = list;
+	return &p[ltype->elems_offset + i * gu_type_size(ltype->elem_type)];
+}
diff --git a/src/runtime/c/gu/list.h b/src/runtime/c/gu/list.h
new file mode 100644
index 000000000..f2add157f
--- /dev/null
+++ b/src/runtime/c/gu/list.h
@@ -0,0 +1,140 @@
+/* 
+ * Copyright 2010 University of Helsinki.
+ *   
+ * This file is part of libgu.
+ * 
+ * Libgu is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ * 
+ * Libgu is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with libgu. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ *
+ * Lists.
+ */
+
+#ifndef GU_LIST_H_
+#define GU_LIST_H_
+
+#include <gu/mem.h>
+
+
+#define GuList(t)	   \
+	struct {	   \
+		const int len;  \
+		t elems[]; \
+	}
+
+void* gu_list_alloc(GuPool* pool, size_t base_size, size_t elem_size, 
+		    int n_elems, size_t alignment);
+
+#define gu_new_list(t, pool, n)						\
+	((t*) gu_list_alloc(pool,					\
+			    sizeof(t),					\
+			    sizeof(((t*)NULL)->elems[0]),		\
+			    (n),					\
+			    gu_flex_alignof(t)))
+
+static inline int
+gu_list_length(const void* list)
+{
+	return *(const int*) list;
+}
+
+#define gu_list_elems(lst) \
+	((lst)->elems)
+
+#define gu_list_index(lst, i) \
+	(gu_list_elems(lst)[i])
+
+typedef GuList(void*) GuPointers; 
+//typedef GuList(uint8_t) GuBytes;
+
+typedef GuList(int) GuInts;		      
+
+
+#define GuListN(t_, len_)			\
+	struct {				\
+	int len;				\
+	t elems[len_];				\
+	}
+
+#define gu_list_(qual_, t_, ...)			\
+	((qual_ GuList(t_) *)				\
+	((qual_ GuListN(t_, (sizeof((t_[]){__VA_ARGS__}) / sizeof(t_)))[]){ \
+	__VA_ARGS__							\
+	}))
+
+#define gu_list(t_, ...)			\
+	gu_list_(, t_, __VA_ARGS__)
+
+#define gu_clist(t_, ...)			\
+	gu_list_(const, t_, __VA_ARGS__)
+			
+#define GuSList(t)				\
+	const struct {				\
+		int len;			\
+		t* elems;			\
+	}
+
+#define GU_SLIST_0 { .len = 0, .elems = NULL }
+
+#define GU_SLIST(t, ...)						\
+	{								\
+		.len = GU_ARRAY_LEN(t,GU_ID({__VA_ARGS__})),		\
+		.elems = ((t[]){__VA_ARGS__})			\
+	}
+
+
+#include <gu/type.h>
+
+//
+// list
+//
+
+typedef const struct GuListType GuListType, GuType_GuList;
+
+struct GuListType {
+	GuType_abstract abstract_base;
+	size_t size;
+	size_t align;
+	GuType* elem_type;
+	ptrdiff_t elems_offset;
+};
+
+#define GU_TYPE_INIT_GuList(k_, t_, elem_type_) {	\
+	.abstract_base = GU_TYPE_INIT_abstract(k_, t_, _),	\
+	.size = sizeof(t_), \
+	.align = gu_alignof(t_),		\
+	.elem_type = elem_type_,	\
+	.elems_offset = offsetof(t_, elems)	\
+}
+
+extern GU_DECLARE_KIND(GuList);
+
+void*
+gu_list_type_alloc(GuListType* ltype, int n_elems, GuPool* pool);
+
+void*
+gu_list_type_index(GuListType* ltype, void* list, int i);
+
+#include <gu/str.h>
+
+
+typedef GuList(GuStr) GuStrs;
+typedef GuStrs* GuStrsP;
+		       
+extern GU_DECLARE_TYPE(GuStrs, GuList);
+extern GU_DECLARE_TYPE(GuStrsP, pointer);
+
+
+#endif // GU_LIST_H_
diff --git a/src/runtime/c/gu/log.c b/src/runtime/c/gu/log.c
new file mode 100644
index 000000000..399646c50
--- /dev/null
+++ b/src/runtime/c/gu/log.c
@@ -0,0 +1,79 @@
+#include <gu/defs.h>
+#include <gu/log.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+static int gu_log_depth = 0;
+
+static bool
+gu_log_match(const char* pat, size_t patlen, const char* str)
+{
+	if (patlen > 0 && pat[patlen-1] == '*') {
+		return strncmp(pat, str, patlen-1) == 0;
+	} else if (strlen(str) == patlen) {
+		return strncmp(pat, str, patlen) == 0;
+	} 
+	return false;
+}
+
+static bool
+gu_log_enabled(const char* func, const char* file)
+{
+	const char* cfg = getenv("GU_LOG");
+	if (cfg == NULL) {
+		return false;
+	}
+	const char* p = cfg;
+	while (true) {
+		size_t len = strcspn(p, ",");
+		if (gu_log_match(p, len, func)) {
+			return true;
+		}
+		if (gu_log_match(p, len, file)) {
+			return true;
+		}
+		if (p[len] == '\0') {
+			break;
+		}
+		p = &p[len + 1];
+	} 
+	return false;
+}
+
+
+void
+gu_log_full_v(GuLogKind kind, const char* func, const char* file, int line,
+	      const char* fmt, va_list args)
+{
+	(void) (kind && line);
+	if (!gu_log_enabled(func, file)) {
+		return;
+	}
+	if (kind == GU_LOG_KIND_EXIT) {
+		gu_log_depth--;
+	}
+	if (fmt) {
+		int indent = gu_min(32 + gu_log_depth, 48);
+		fprintf(stderr, "%-*s: ", indent, func);
+		vfprintf(stderr, fmt, args);
+		fputc('\n', stderr);
+		fflush(stderr);
+	}
+	if (kind == GU_LOG_KIND_ENTER) {
+		gu_log_depth++;
+	}
+}
+
+void
+gu_log_full(GuLogKind kind, const char* func, const char* file, int line,
+	    const char* fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	gu_log_full_v(kind, func, file, line, fmt, args);
+	va_end(args);
+}
+
diff --git a/src/runtime/c/gu/log.h b/src/runtime/c/gu/log.h
new file mode 100644
index 000000000..ec9ecdf75
--- /dev/null
+++ b/src/runtime/c/gu/log.h
@@ -0,0 +1,65 @@
+#ifndef GU_LOG_H_
+#define GU_LOG_H_
+
+#include <stdarg.h>
+
+typedef enum GuLogKind {
+	GU_LOG_KIND_ENTER,
+	GU_LOG_KIND_EXIT,
+	GU_LOG_KIND_DEBUG,
+	GU_LOG_KIND_ERROR
+} GuLogKind;
+
+void
+gu_log_full(GuLogKind kind, const char* func, const char* file, int line,
+	    const char* fmt, ...);
+
+
+void
+gu_log_full_v(GuLogKind kind, const char* func, const char* file, int line,
+	      const char* fmt, va_list args);
+
+
+#ifndef NDEBUG
+
+#define gu_logv(kind_, fmt_, args_)					\
+	gu_log_full_v(kind_, __func__, __FILE__, __LINE__, fmt_, args_)
+
+#define gu_log(kind_, ...)			\
+	gu_log_full(kind_, __func__, __FILE__, __LINE__, __VA_ARGS__)
+
+#else
+
+static inline void
+gu_logv(GuLogKind kind, const char* fmt, va_list args)
+{
+	(void) kind;
+	(void) fmt;
+	(void) args;
+}
+
+static inline void
+gu_log(GuLogKind kind, const char* fmt, ...)
+{
+	(void) kind;
+	(void) fmt;
+}
+
+#endif
+
+
+
+
+#define gu_enter(...)			\
+	gu_log(GU_LOG_KIND_ENTER, __VA_ARGS__)
+
+#define gu_exit(...)				\
+	gu_log(GU_LOG_KIND_EXIT, __VA_ARGS__)
+
+#define gu_debug(...)				\
+	gu_log(GU_LOG_KIND_DEBUG, __VA_ARGS__)
+
+#define gu_debugv(kind_, fmt_, args_) \
+	gu_logv(GU_LOG_KIND_DEBUG, fmt_, args_)
+
+#endif // GU_LOG_H_
diff --git a/src/runtime/c/gu/map.c b/src/runtime/c/gu/map.c
new file mode 100644
index 000000000..2ee77bb23
--- /dev/null
+++ b/src/runtime/c/gu/map.c
@@ -0,0 +1,353 @@
+#include <gu/defs.h>
+#include <gu/mem.h>
+#include <gu/type.h>
+#include <gu/map.h>
+#include <gu/assert.h>
+#include <gu/prime.h>
+#include <gu/log.h>
+
+typedef enum {
+	GU_MAP_GENERIC,
+	GU_MAP_ADDR,
+	GU_MAP_WORD
+} GuMapKind;
+
+typedef struct GuMapData GuMapData;
+
+struct GuMapData {
+	uint8_t* keys;
+	uint8_t* values;
+	size_t n_occupied;
+	size_t n_entries;
+	size_t zero_idx;
+};
+
+struct GuMap {
+	GuMapKind const kind;
+	GuHasher* const hasher;
+	size_t const key_size;
+	size_t const value_size;
+	const void* default_value;
+	GuMapData data;
+	
+	GuFinalizer fin;
+};
+
+static void
+gu_map_finalize(GuFinalizer* fin)
+{
+	GuMap* map = gu_container(fin, GuMap, fin);
+	gu_mem_buf_free(map->data.keys);
+	if (map->value_size) {
+		gu_mem_buf_free(map->data.values);
+	}
+}
+
+static const GuWord gu_map_empty_key = 0;
+
+static bool
+gu_map_buf_is_zero(const uint8_t* p, size_t sz) {
+	while (sz >= sizeof(GuWord)) {
+		sz -= sizeof(GuWord);
+		if (memcmp(&p[sz], &gu_map_empty_key, sizeof(GuWord)) != 0) {
+			return false;
+		}
+	}
+	return (memcmp(p, &gu_map_empty_key, sz) == 0);
+}
+
+static bool
+gu_map_entry_is_free(GuMap* map, GuMapData* data, size_t idx)
+{
+	if (idx == data->zero_idx) {
+		return false;
+	} else if (map->kind == GU_MAP_ADDR) {
+		const void* key = ((const void**)data->keys)[idx];
+		return key == NULL;
+	} else if (map->kind == GU_MAP_WORD) {
+		GuWord key = ((GuWord*)data->keys)[idx];
+		return key == 0;
+	}
+	gu_assert(map->kind == GU_MAP_GENERIC);
+	const void* key = &data->keys[idx * map->key_size];
+	return gu_map_buf_is_zero(key, map->key_size);
+}
+
+static bool
+gu_map_lookup(GuMap* map, const void* key, size_t* idx_out)
+{
+	size_t n = map->data.n_entries;
+	switch (map->kind) {
+	case GU_MAP_GENERIC: {
+		GuHasher* hasher = map->hasher;
+		GuEquality* eq = (GuEquality*) hasher;
+		GuHash hash = hasher->hash(hasher, key);
+		size_t idx = hash % n;
+		size_t offset = (hash % (n - 2)) + 1;
+		size_t key_size = map->key_size;
+		while (true) {
+			void* entry_key = &map->data.keys[idx * key_size];
+			if (gu_map_buf_is_zero(entry_key, key_size) &&
+			    map->data.zero_idx != idx) {
+				*idx_out = idx;
+				return false;
+			} else if (eq->is_equal(eq, key, entry_key)) {
+				*idx_out = idx;
+				return true;
+			}
+			idx = (idx + offset) % n;
+		}
+		gu_impossible();
+		break;
+	}
+	case GU_MAP_ADDR: {
+		GuHash hash = (GuHash) key;
+		size_t idx = hash % n;
+		size_t offset = (hash % (n - 2)) + 1;
+		while (true) {
+			const void* entry_key =
+				((const void**)map->data.keys)[idx];
+			if (entry_key == NULL && map->data.zero_idx != idx) {
+				*idx_out = idx;
+				return false;
+			} else if (entry_key == key) {
+				*idx_out = idx;
+				return true;
+			}
+			idx = (idx + offset) % n;
+		}
+		gu_impossible();
+		break;
+	}
+	case GU_MAP_WORD: {
+		GuWord w = *(const GuWord*)key;
+		GuHash hash = (GuHash) w;
+		size_t idx = hash % n;
+		size_t offset = (hash % (n - 2)) + 1;
+		while (true) {
+			GuWord entry_key = ((GuWord*)map->data.keys)[idx];
+			if (entry_key == 0 && map->data.zero_idx != idx) {
+				*idx_out = idx;
+				return false;
+			} else if (entry_key == w) {
+				*idx_out = idx;
+				return true;
+			}
+			idx = (idx + offset) % n;
+		}
+		gu_impossible();
+		break;
+	}
+	default:
+		gu_impossible();
+	}
+	gu_impossible();
+	return false;
+}
+	
+
+static void
+gu_map_resize(GuMap* map)
+{
+	GuMapData* data = &map->data;
+	GuMapData old_data = *data;
+	size_t req_entries =
+		gu_twin_prime_sup(GU_MAX(11, map->data.n_occupied * 4 / 3 + 1));
+
+	size_t key_size = map->key_size;
+	size_t key_alloc = 0;
+	data->keys = gu_mem_buf_alloc(req_entries * key_size, &key_alloc);
+
+	size_t value_size = map->value_size;
+	size_t value_alloc = 0;
+	if (value_size) {
+		data->values = gu_mem_buf_alloc(req_entries * value_size,
+						    &value_alloc);
+		memset(data->values, 0, value_alloc);
+	}
+	
+	data->n_entries = gu_twin_prime_inf(value_size ?
+					    GU_MIN(key_alloc / key_size,
+						   value_alloc / value_size)
+					    : key_alloc / key_size);
+	switch (map->kind) {
+	case GU_MAP_GENERIC:
+	case GU_MAP_WORD:
+		memset(data->keys, 0, key_alloc);
+		break;
+	case GU_MAP_ADDR:
+		for (size_t i = 0; i < data->n_entries; i++) {
+			((const void**)data->keys)[i] = NULL;
+		}
+		break;
+	default:
+		gu_impossible();
+	}
+
+	gu_assert(data->n_entries > data->n_occupied);
+	gu_debug("Resized to %d entries", data->n_entries);
+	
+	data->n_occupied = 0;
+	data->zero_idx = SIZE_MAX;
+
+	for (size_t i = 0; i < old_data.n_entries; i++) {
+		if (gu_map_entry_is_free(map, &old_data, i)) {
+			continue;
+		}
+		void* old_key = &old_data.keys[i * key_size];
+		if (map->kind == GU_MAP_ADDR) {
+			old_key = *(void**)old_key;
+		}
+		void* old_value = &old_data.values[i * value_size];
+
+		memcpy(gu_map_insert(map, old_key),
+		       old_value, map->value_size);
+	}
+
+	gu_mem_buf_free(old_data.keys);
+	if (value_size) {
+		gu_mem_buf_free(old_data.values);
+	}
+}
+
+
+static bool
+gu_map_maybe_resize(GuMap* map)
+{
+	if (map->data.n_entries <=
+	    map->data.n_occupied + (map->data.n_occupied / 4)) {
+		gu_map_resize(map);
+		return true;
+	}
+	return false;
+}
+
+void*
+gu_map_find(GuMap* map, const void* key)
+{
+	size_t idx;
+	bool found = gu_map_lookup(map, key, &idx);
+	if (found) {
+		return &map->data.values[idx * map->value_size];
+	}
+	return NULL;
+}
+
+const void*
+gu_map_find_default(GuMap* map, const void* key)
+{
+	void* p = gu_map_find(map, key);
+	return p ? p : map->default_value;
+}
+
+const void*
+gu_map_find_key(GuMap* map, const void* key)
+{
+	size_t idx;
+	bool found = gu_map_lookup(map, key, &idx);
+	if (found) {
+		return &map->data.keys[idx * map->key_size];
+	}
+	return NULL;
+}
+
+
+void*
+gu_map_insert(GuMap* map, const void* key)
+{
+	size_t idx;
+	bool found = gu_map_lookup(map, key, &idx);
+	if (!found) {
+		if (gu_map_maybe_resize(map)) {
+			found = gu_map_lookup(map, key, &idx);
+			gu_assert(!found);
+		}
+		if (map->kind == GU_MAP_ADDR) {
+			((const void**)map->data.keys)[idx] = key;
+		} else {
+			memcpy(&map->data.keys[idx * map->key_size],
+			       key, map->key_size);
+		}
+		if (map->default_value) {
+			memcpy(&map->data.values[idx * map->value_size],
+			       map->default_value, map->value_size);
+		}
+		if (gu_map_entry_is_free(map, &map->data, idx)) {
+			gu_assert(map->data.zero_idx == SIZE_MAX);
+			map->data.zero_idx = idx;
+		}
+		map->data.n_occupied++;
+	}
+	return &map->data.values[idx * map->value_size];
+}
+
+void
+gu_map_iter(GuMap* map, GuMapItor* itor, GuExn* err)
+{
+	for (size_t i = 0; i < map->data.n_entries && gu_ok(err); i++) {
+		if (gu_map_entry_is_free(map, &map->data, i)) {
+			continue;
+		}
+		const void* key = &map->data.keys[i * map->key_size];
+		void* value = &map->data.values[i * map->value_size];
+		if (map->kind == GU_MAP_ADDR) {
+			key = *(const void* const*) key;
+		}
+		itor->fn(itor, key, value, err);
+	}
+}
+
+static const uint8_t gu_map_no_values[1] = { 0 };
+
+GuMap*
+gu_make_map(size_t key_size, GuHasher* hasher,
+	    size_t value_size, const void* default_value,
+	    GuPool* pool)
+{
+	GuMapKind kind =
+		((!hasher || hasher == gu_addr_hasher)
+		 ? GU_MAP_ADDR
+		 : (key_size == sizeof(GuWord) && hasher == gu_word_hasher)
+		 ? GU_MAP_WORD
+		 : GU_MAP_GENERIC);
+	if (kind == GU_MAP_ADDR) {
+		key_size = sizeof(GuWord);
+	}
+	GuMapData data = {
+		.n_occupied = 0,
+		.n_entries = 0,
+		.keys = NULL,
+		.values = value_size ? NULL : (uint8_t*) gu_map_no_values,
+		.zero_idx = SIZE_MAX
+	};
+	GuMap* map = gu_new_i(
+		pool, GuMap,
+		.default_value = default_value,
+		.hasher = hasher,
+		.data = data,
+		.key_size = key_size,
+		.value_size = value_size,
+		.fin.fn = gu_map_finalize,
+		.kind = kind
+		);
+	gu_pool_finally(pool, &map->fin);
+	gu_map_resize(map);
+	return map;
+}
+
+GuMap*
+gu_map_type_make(GuMapType* mtype, GuPool* pool)
+{
+	size_t key_size = 0;
+	if (mtype->hasher && mtype->hasher != gu_addr_hasher) {
+		key_size = gu_type_size(mtype->key_type);
+	}
+	size_t value_size = gu_type_size(mtype->value_type);
+	return gu_make_map(key_size, mtype->hasher,
+			   value_size, mtype->default_value, pool);
+}
+
+GU_DEFINE_KIND(GuMap, abstract);
+// GU_DEFINE_KIND(GuIntMap, GuMap);
+
+
diff --git a/src/runtime/c/gu/map.h b/src/runtime/c/gu/map.h
new file mode 100644
index 000000000..6523a8057
--- /dev/null
+++ b/src/runtime/c/gu/map.h
@@ -0,0 +1,121 @@
+#ifndef GU_MAP_H_
+#define GU_MAP_H_
+
+#include <gu/hash.h>
+#include <gu/mem.h>
+#include <gu/exn.h>
+
+typedef const struct GuMapItor GuMapItor;
+
+struct GuMapItor {
+	void (*fn)(GuMapItor* self, const void* key, void* value,
+		   GuExn *err);
+};
+
+typedef struct GuMap GuMap;
+
+GuMap*
+gu_make_map(size_t key_size, GuHasher* hasher,
+	    size_t value_size, const void* default_value,
+	    GuPool* pool);
+
+#define gu_new_map(K, HASHER, V, DV, POOL)			\
+	(gu_make_map(sizeof(K), (HASHER), sizeof(V), (DV), (POOL)))
+
+#define gu_new_set(K, HASHER, POOL)			\
+	(gu_make_map(sizeof(K), (HASHER), 0, NULL, (POOL)))
+
+#define gu_new_addr_map(K, V, DV, POOL)				\
+	(gu_make_map(0, NULL, sizeof(V), (DV), (POOL)))
+
+size_t
+gu_map_count(GuMap* map);
+
+void*
+gu_map_find_full(GuMap* ht, void* key_inout);
+
+const void*
+gu_map_find_default(GuMap* ht, const void* key);
+
+#define gu_map_get(MAP, KEYP, V)		\
+	(*(V*)gu_map_find_default((MAP), (KEYP)))
+
+void*
+gu_map_find(GuMap* ht, const void* key);
+
+#define gu_map_set(MAP, KEYP, V, VAL)				\
+	GU_BEGIN						\
+	V* gu_map_set_p_ = gu_map_find((MAP), (KEYP));		\
+	*gu_map_set_p_ = (VAL);					\
+	GU_END
+
+const void*
+gu_map_find_key(GuMap* ht, const void* key);
+
+static inline bool
+gu_map_has(GuMap* ht, const void* key)
+{
+	return gu_map_find_key(ht, key) != NULL;
+}
+
+
+void*
+gu_map_insert(GuMap* ht, const void* key);
+
+#define gu_map_put(MAP, KEYP, V, VAL)				\
+	GU_BEGIN						\
+	V* gu_map_put_p_ = gu_map_insert((MAP), (KEYP));	\
+	*gu_map_put_p_ = (VAL);					\
+	GU_END
+
+void
+gu_map_iter(GuMap* ht, GuMapItor* itor, GuExn* err);
+
+
+typedef GuMap GuIntMap;
+
+#define gu_new_int_map(VAL_T, DEFAULT, POOL)		\
+	gu_new_map(int, gu_int_hasher, VAL_T, DEFAULT, POOL)
+
+
+#if defined(GU_TYPE_H_) && !defined(GU_MAP_H_TYPE_)
+#define GU_MAP_H_TYPE_
+
+extern GU_DECLARE_KIND(GuMap);
+
+typedef const struct GuMapType GuMapType, GuType_GuMap;
+
+struct GuMapType {
+	GuType_abstract abstract_base;
+	GuHasher* hasher;
+	GuType* key_type;
+	GuType* value_type;
+	const void* default_value;
+};
+
+GuMap*
+gu_map_type_make(GuMapType* mtype, GuPool* pool);
+
+#define gu_map_type_new(MAP_T, POOL)			\
+	gu_map_type_make(gu_type_cast(gu_type(MAP_T), GuMap), (POOL))
+
+#define GU_TYPE_INIT_GuMap(k_, t_, kt_, h_, vt_, dv_)			\
+	{								\
+		.abstract_base = GU_TYPE_INIT_abstract(k_, t_, _),	\
+		.hasher = h_,						\
+		.key_type = kt_,					\
+		.value_type = vt_,					\
+		.default_value = dv_					\
+	}
+
+#define gu_type__GuIntMap gu_type__GuMap
+
+typedef GuType_GuMap GuType_GuIntMap;
+
+#define GU_TYPE_INIT_GuIntMap(KIND, MAP_T, VAL_T, DEFAULT)	\
+	GU_TYPE_INIT_GuMap(KIND, MAP_T, gu_type(int), gu_int_hasher,	\
+			   VAL_T, DEFAULT)
+
+#endif
+
+#endif // GU_MAP_H_
diff --git a/src/runtime/c/gu/mem.c b/src/runtime/c/gu/mem.c
new file mode 100644
index 000000000..649105a6a
--- /dev/null
+++ b/src/runtime/c/gu/mem.c
@@ -0,0 +1,346 @@
+/* 
+ * Copyright 2010 University of Helsinki.
+ *   
+ * This file is part of libgu.
+ * 
+ * Libgu is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ * 
+ * Libgu is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with libgu. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <gu/mem.h>
+#include <gu/fun.h>
+#include <gu/bits.h>
+#include <gu/assert.h>
+#include <gu/log.h>
+#include <string.h>
+#include <stdlib.h>
+
+#ifdef USE_VALGRIND
+#include <valgrind/valgrind.h>
+#define VG(X) X
+#else
+#define VG(X) GU_NOP
+#endif
+
+static const size_t
+// Maximum request size for a chunk. The actual maximum chunk size
+// may be somewhat larger.
+gu_mem_chunk_max_size = 1024 * sizeof(void*),
+
+// number of bytes to allocate in the pool when it is created
+	gu_mem_pool_initial_size = 24 * sizeof(void*),
+
+// Pool allocations larger than this will get their own chunk if
+// there's no room in the current one. Allocations smaller than this may trigger
+// the creation of a new chunk, in which case the remaining space in
+// the current chunk is left unused (internal fragmentation).
+	gu_mem_max_shared_alloc = 64 * sizeof(void*),
+	
+// Should not be smaller than the granularity for malloc
+	gu_mem_unit_size = 2 * sizeof(void*),
+
+/* Malloc tuning: the additional memory used by malloc next to the
+   allocated object */
+	gu_malloc_overhead = sizeof(size_t);
+
+static void*
+gu_mem_realloc(void* p, size_t size)
+{
+	void* buf = realloc(p, size);
+	if (size != 0 && buf == NULL) {
+		gu_fatal("Memory allocation failed");
+	}
+	gu_debug("%p %zu -> %p", p, size, buf); // strictly illegal
+	return buf;
+}
+
+static void*
+gu_mem_alloc(size_t size)
+{
+	void* buf = malloc(size);
+	if (buf == NULL) {
+		gu_fatal("Memory allocation failed");
+	}
+	gu_debug("%zu -> %p", size, buf);
+	return buf;
+}
+
+static void
+gu_mem_free(void* p)
+{
+	gu_debug("%p", p);
+	free(p);
+}
+
+static size_t
+gu_mem_padovan(size_t min)
+{
+	// This could in principle be done faster with Q-matrices for
+	// Padovan numbers, but not really worth it for our commonly
+	// small numbers.
+	if (min <= 5) {
+		return min;
+	}
+	size_t a = 7, b = 9, c = 12;
+	while (min > a) {
+		if (b < a) {
+			// overflow
+			return SIZE_MAX;
+		}
+		size_t tmp = a + b;
+		a = b;
+		b = c;
+		c = tmp;
+	}
+	return a;
+}
+
+void*
+gu_mem_buf_realloc(void* old_buf, size_t min_size, size_t* real_size_out)
+{
+	size_t min_blocks = ((min_size + gu_malloc_overhead - 1) /
+			     gu_mem_unit_size) + 1;
+	size_t blocks = gu_mem_padovan(min_blocks);
+	size_t size = blocks * gu_mem_unit_size - gu_malloc_overhead;
+	void* buf = gu_mem_realloc(old_buf, size);
+	*real_size_out = buf ? size : 0;
+	return buf;
+}
+void*
+gu_mem_buf_alloc(size_t min_size, size_t* real_size_out)
+{
+	return gu_mem_buf_realloc(NULL, min_size, real_size_out);
+}
+
+void
+gu_mem_buf_free(void* buf)
+{
+	gu_mem_free(buf);
+}
+
+
+typedef struct GuMemChunk GuMemChunk;
+
+struct GuMemChunk {
+	GuMemChunk* next;
+	uint8_t data[];
+};
+
+typedef struct GuFinalizerNode GuFinalizerNode;
+
+struct GuFinalizerNode {
+	GuFinalizerNode* next;
+	GuFinalizer* fin;
+};
+
+enum GuPoolFlags {
+	GU_POOL_LOCAL = 1 << 0
+};
+
+struct GuPool {
+	uint8_t* curr_buf; // actually GuMemChunk*
+	GuMemChunk* chunks;
+	GuFinalizerNode* finalizers;
+	uint16_t flags;
+	uint16_t left_edge;
+	uint16_t right_edge;
+	uint16_t curr_size;
+	uint8_t init_buf[];
+};
+
+static GuPool*
+gu_init_pool(uint8_t* buf, size_t sz)
+{
+	gu_require(gu_aligned((uintptr_t) (void*) buf, gu_alignof(GuPool)));
+	gu_require(sz >= sizeof(GuPool));
+	GuPool* pool = (GuPool*) buf;
+	pool->flags = 0;
+	pool->curr_size = sz;
+	pool->curr_buf = (uint8_t*) pool;
+	pool->chunks = NULL;
+	pool->finalizers = NULL;
+	pool->left_edge = offsetof(GuPool, init_buf);
+	pool->right_edge = sz;
+	VG(VALGRIND_CREATE_MEMPOOL(pool, 0, false));
+	return pool;
+}
+
+GuPool*
+gu_local_pool_(uint8_t* buf, size_t sz)
+{
+	GuPool* pool = gu_init_pool(buf, sz);
+	pool->flags |= GU_POOL_LOCAL;
+	gu_debug("%p", pool);
+	return pool;
+}
+
+GuPool* 
+gu_new_pool(void)
+{
+	size_t sz = GU_FLEX_SIZE(GuPool, init_buf, gu_mem_pool_initial_size);
+	uint8_t* buf = gu_mem_buf_alloc(sz, &sz);
+	GuPool* pool = gu_init_pool(buf, sz);
+	gu_debug("%p", pool);
+	return pool;
+}
+
+static void
+gu_pool_expand(GuPool* pool, size_t req)
+{
+	size_t real_req = GU_MAX(req, GU_MIN(((size_t)pool->curr_size) + 1,
+					     gu_mem_chunk_max_size));
+	gu_assert(real_req >= sizeof(GuMemChunk));
+	size_t size = 0;
+	GuMemChunk* chunk = gu_mem_buf_alloc(real_req, &size);
+	chunk->next = pool->chunks;
+	pool->chunks = chunk;
+	pool->curr_buf = (uint8_t*) chunk;
+	pool->left_edge = offsetof(GuMemChunk, data);
+	pool->right_edge = pool->curr_size = size;
+	// size should always fit in uint16_t
+	gu_assert((size_t) pool->right_edge == size); 
+}
+
+static size_t
+gu_mem_advance(size_t old_pos, size_t pre_align, size_t pre_size,
+	       size_t align, size_t size)
+{
+	size_t p = gu_align_forward(old_pos, pre_align);
+	p += pre_size;
+	p = gu_align_forward(p, align);
+	p += size;
+	return p;
+}
+
+static void*
+gu_pool_malloc_aligned(GuPool* pool, size_t pre_align, size_t pre_size,
+		       size_t align, size_t size) 
+{
+	gu_require(size <= gu_mem_max_shared_alloc);
+	size_t pos = gu_mem_advance(pool->left_edge, pre_align, pre_size,
+				    align, size);
+	if (pos > (size_t) pool->right_edge) {
+		pos = gu_mem_advance(offsetof(GuMemChunk, data),
+				     pre_align, pre_size, align, size);
+		gu_pool_expand(pool, pos);
+		gu_assert(pos <= pool->right_edge);
+	}
+	pool->left_edge = pos;
+	uint8_t* addr = &pool->curr_buf[pos - size];
+	VG(VALGRIND_MEMPOOL_ALLOC(pool, addr - pre_size, size + pre_size ));
+	return addr;
+}
+
+static size_t
+gu_pool_avail(GuPool* pool)
+{
+	return (size_t) pool->right_edge - (size_t) pool->left_edge;
+}
+
+void*
+gu_pool_malloc_unaligned(GuPool* pool, size_t size)
+{
+	if (size > gu_pool_avail(pool)) {
+		gu_pool_expand(pool, offsetof(GuMemChunk, data) + size);
+		gu_assert(size <= gu_pool_avail(pool));
+	}
+	pool->right_edge -= size;
+	void* addr = &pool->curr_buf[pool->right_edge];
+	VG(VALGRIND_MEMPOOL_ALLOC(pool, addr, size));
+	return addr;
+}
+
+void*
+gu_malloc_prefixed(GuPool* pool, size_t pre_align, size_t pre_size,
+		   size_t align, size_t size)
+{
+	gu_enter("-> %p %zu %zu %zu %zu",
+		 pool, pre_align, pre_size, align, size);
+	void* ret = NULL;
+	if (pre_align == 0) {
+		pre_align = gu_alignof(GuMaxAlign);
+	}
+	if (align == 0) {
+		align = gu_alignof(GuMaxAlign);
+	}
+	size_t full_size = gu_mem_advance(offsetof(GuMemChunk, data),
+					  pre_align, pre_size, align, size);
+	if (full_size > gu_mem_max_shared_alloc) {
+		GuMemChunk* chunk = gu_mem_alloc(full_size);
+		chunk->next = pool->chunks;
+		pool->chunks = chunk;
+		uint8_t* addr = &chunk->data[full_size - size
+					     - offsetof(GuMemChunk, data)];
+		VG(VALGRIND_MEMPOOL_ALLOC(pool, addr - pre_size,
+					  pre_size + size));
+		ret = addr;
+	} else if (pre_align == 1 && align == 1) {
+		uint8_t* buf = gu_pool_malloc_unaligned(pool, pre_size + size);
+		ret = &buf[pre_size];
+	} else {
+		ret = gu_pool_malloc_aligned(pool, pre_align, pre_size,
+					     align, size);
+	}
+	gu_exit("<- %p", ret);
+	return ret;
+}
+
+void*
+gu_malloc_aligned(GuPool* pool, size_t size, size_t align)
+{
+	if (align == 0) {
+		align = GU_MIN(size, gu_alignof(GuMaxAlign));
+	}
+	void* ret = gu_malloc_prefixed(pool, 1, 0, align, size);
+	return ret;
+}
+
+
+void 
+gu_pool_finally(GuPool* pool, GuFinalizer* finalizer)
+{
+	GuFinalizerNode* node = gu_new(GuFinalizerNode, pool);
+	node->next = pool->finalizers;
+	node->fin = finalizer;
+	pool->finalizers = node;
+}
+
+void
+gu_pool_free(GuPool* pool)
+{
+	gu_debug("%p", pool);
+	GuFinalizerNode* node = pool->finalizers;
+	while (node) {
+		GuFinalizerNode* next = node->next;
+		node->fin->fn(node->fin);
+		node = next;
+	}
+	GuMemChunk* chunk = pool->chunks;
+	while (chunk) {
+		GuMemChunk* next = chunk->next;
+		gu_mem_buf_free(chunk);
+		chunk = next;
+	}
+	VG(VALGRIND_DESTROY_MEMPOOL(pool));
+	if (!pool->flags & GU_POOL_LOCAL) {
+		gu_mem_buf_free(pool);
+	}
+}
+
+
+extern inline void* gu_malloc(GuPool* pool, size_t size);
+
+extern inline void* 
+gu_malloc_init_aligned(GuPool* pool, size_t size, size_t alignment, 
+		       const void* init);
+
diff --git a/src/runtime/c/gu/mem.h b/src/runtime/c/gu/mem.h
new file mode 100644
index 000000000..4369f4036
--- /dev/null
+++ b/src/runtime/c/gu/mem.h
@@ -0,0 +1,276 @@
+/* 
+ * Copyright 2010 University of Helsinki.
+ *   
+ * This file is part of libgu.
+ * 
+ * Libgu is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ * 
+ * Libgu is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with libgu. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ *
+ * Memory allocation tools.
+ */
+
+#ifndef GU_MEM_H_
+#define GU_MEM_H_
+
+#include <gu/defs.h>
+#include <gu/fun.h>
+
+/** @defgroup GuPool Memory pools */
+//@{ 
+
+
+/// A memory pool.
+typedef struct GuPool GuPool;
+
+/// @name Creating a pool 
+//@{
+
+
+/// Create a new memory pool.
+GU_ONLY GuPool*
+gu_new_pool(void);
+
+/**< 
+ * @return A new memory pool.
+ */
+
+
+//@private
+GuPool*
+gu_local_pool_(uint8_t* init_buf, size_t sz);
+
+//@private
+#define GU_LOCAL_POOL_INIT_SIZE (16 * sizeof(GuWord))
+
+
+/// Create a stack-allocated memory pool.
+#define gu_local_pool()				\
+	gu_local_pool_(gu_alloca(GU_LOCAL_POOL_INIT_SIZE),	\
+		       GU_LOCAL_POOL_INIT_SIZE)
+/**<
+ * @return A memory pool whose first chunk is allocated directly from
+ * the stack. This makes its creation faster, and more suitable for
+ * functions that usually allocate only a little memory from the pool
+ * until it is freed.
+ *
+ * @note The pool created with #gu_local_pool \e must be freed with
+ * #gu_pool_free before the end of the block where #gu_local_pool was
+ * called.
+ *
+ * @note Because #gu_local_pool uses relatively much stack space, it
+ * should not be used in the bodies of recursive functions.
+ */
+
+
+//@}
+/// @name Destroying a pool
+//@{
+
+
+/// Free a memory pool and all objects allocated from it.
+void
+gu_pool_free(GU_ONLY GuPool* pool);
+/**<
+ * When the pool is freed, all finalizers registered by
+ * #gu_pool_finally on \p pool are invoked in reverse order of
+ * registration.
+ * 
+ * @note After the pool is freed, all objects allocated from it become
+ * invalid and may no longer be used. */
+
+//@}
+/// @name Allocating from a pool
+//@{
+ 
+
+/// Allocate memory with a specified alignment.
+void* 
+gu_malloc_aligned(GuPool* pool, size_t size, size_t alignment); 
+
+void*
+gu_malloc_prefixed(GuPool* pool, size_t pre_align, size_t pre_size,
+		   size_t align, size_t size);
+
+/// Allocate memory from a pool.
+inline void*
+gu_malloc(GuPool* pool, size_t size) {
+	return gu_malloc_aligned(pool, size, 0);
+}
+
+#include <string.h>
+
+//@private
+static inline void*
+gu_malloc_init_aligned(GuPool* pool, size_t size, size_t alignment, 
+		       const void* init)
+{
+	void* p = gu_malloc_aligned(pool, size, alignment);
+	memcpy(p, init, size);
+	return p;
+}
+
+//@private
+static inline void*
+gu_malloc_init(GuPool* pool, size_t size, const void* init)
+{
+	return gu_malloc_init_aligned(pool, size, 0, init);
+}
+
+
+/** Allocate memory to store an array of objects of a given type. */
+
+#define gu_new_n(type, n, pool)						\
+	((type*)gu_malloc_aligned((pool),				\
+				  sizeof(type) * (n),			\
+				  gu_alignof(type)))
+/**< 
+ * @param type  The C type of the objects to allocate.
+ *
+ * @param n     The number of objects to allocate.
+ * 
+ * @param pool  The memory pool to allocate from.
+ *
+ * @return A pointer to a heap-allocated array of \p n uninitialized
+ * objects of type \p type. 
+ */ 
+
+
+/** Allocate memory to store an object of a given type. */
+
+#define gu_new(type, pool) \
+	gu_new_n(type, 1, pool)
+/**< 
+ * @param type  The C type of the object to allocate.
+ *
+ * @param pool  The memory pool to allocate from.
+ *
+ * @return A pointer to a heap-allocated uninitialized object of type
+ * \p type.
+ */
+
+
+#define gu_new_prefixed(pre_type, type, pool)				\
+	((type*)(gu_malloc_prefixed((pool),				\
+				    gu_alignof(pre_type), sizeof(pre_type), \
+				    gu_alignof(type), sizeof(type))))
+
+
+	
+
+
+#ifdef GU_HAVE_STATEMENT_EXPRESSIONS
+#define gu_new_i(pool, type, ...)					\
+	({								\
+		type *gu_new_p_ = gu_new(type, pool);			\
+		memcpy((void*) gu_new_p_, &(type){ __VA_ARGS__ },	\
+		       sizeof(type));					\
+		gu_new_p_;						\
+	})
+#else // GU_HAVE_STATEMENT_EXPRESSIONS
+#define gu_new_i(pool, type, ...)					\
+	((type*)gu_malloc_init_aligned((pool), sizeof(type),		\
+				       gu_alignof(type),		\
+				       &(type){ __VA_ARGS__ }))
+#endif // GU_HAVE_STATEMENT_EXPRESSIONS
+
+/** @def gu_new_i(pool, type, ...)
+ *
+ * Allocate and initialize an object.
+ *
+ * @param pool The pool to allocate from.
+ *
+ * @param type The C type of the object to allocate.
+ *
+ * @param ... An initializer list for the object to allocate.
+ */
+
+#define gu_new_s gu_new_i
+
+// Alas, there's no portable way to get the alignment of flex structs.
+#define gu_new_flex(pool_, type_, flex_member_, n_elems_)		\
+	((type_ *)gu_malloc_aligned(					\
+		(pool_),						\
+		GU_FLEX_SIZE(type_, flex_member_, n_elems_),		\
+		gu_flex_alignof(type_)))
+
+
+//@}
+/// @name Finalizers
+//@{
+
+
+typedef struct GuFinalizer GuFinalizer;
+
+struct GuFinalizer {
+	void (*fn)(GuFinalizer* self);
+	///< @param self A pointer to this finalizer.
+};
+
+/// Register a finalizer.
+void gu_pool_finally(GuPool* pool, GuFinalizer* fini);
+
+/**< Register \p fini to be called when \p pool is destroyed. The
+ * finalizers are called in reverse order of registration.
+ */
+
+
+//@}
+//@}
+
+/** @defgroup GuMemBuf Memory buffers
+ *
+ * Resizable blocks of heap-allocated memory. These operations differ
+ * from standard \c malloc, \c realloc and \c free -functions in that
+ * memory buffers are not allocated by exact size. Instead, a minimum
+ * size is requested, and the returned buffer may be larger. This
+ * gives the memory allocator more flexibility when the client code
+ * can make use of larger buffers than requested.
+ * */
+
+//@{
+
+
+/// Allocate a new memory buffer.
+GU_ONLY void*
+gu_mem_buf_alloc(size_t min_size, size_t* real_size);
+/**<
+ * @param min_size The minimum acceptable size for a returned memory block.
+ *
+ * @param[out] real_size The actual size of the returned memory
+ * block. This is never less than \p min_size.
+ *
+ * @return A pointer to the memory buffer.
+ */
+
+
+/// Allocate a new memory buffer to replace an old one.
+GU_ONLY void*
+gu_mem_buf_realloc(
+	GU_NULL GU_ONLY GU_RETURNED
+	void* buf,
+	size_t min_size,
+	size_t* real_size_out);
+
+
+/// Free a memory buffer.
+void
+gu_mem_buf_free(GU_ONLY void* buf);
+
+
+//@}
+
+
+#endif // GU_MEM_H_
diff --git a/src/runtime/c/gu/out.c b/src/runtime/c/gu/out.c
new file mode 100644
index 000000000..61df2c184
--- /dev/null
+++ b/src/runtime/c/gu/out.c
@@ -0,0 +1,302 @@
+#include <gu/seq.h>
+#include <gu/out.h>
+
+
+
+GuOut
+gu_init_out(GuOutStream* stream)
+{
+	gu_require(stream != NULL);
+	GuOut out = {
+		.buf_end = NULL,
+		.buf_curr = 0,
+		.stream = stream,
+		.fini.fn = NULL
+	};
+	return out;
+}
+
+static bool
+gu_out_is_buffering(GuOut* out)
+{
+	return !!out->buf_end;
+}
+
+
+static void
+gu_out_end_buf(GuOut* out, GuExn* err)
+{
+	if (!gu_out_is_buffering(out)) {
+		return;
+	}
+	GuOutStream* stream = out->stream;
+	size_t curr_len = ((ptrdiff_t)out->buf_size) + out->buf_curr;
+	stream->end_buf(stream, curr_len, err);
+	out->buf_end = NULL;
+	out->buf_size = out->buf_curr = 0;
+}
+
+static bool
+gu_out_begin_buf(GuOut* out, size_t req, GuExn* err)
+{
+	GuOutStream* stream = out->stream;
+	if (gu_out_is_buffering(out)) {
+		if (out->buf_curr < 0) {
+			return true;
+		} else {
+			gu_out_end_buf(out, err);
+			if (!gu_ok(err)) {
+				return false;
+			}
+		}
+	}
+	if (stream->begin_buf) {
+		size_t sz = 0;
+		uint8_t* buf = stream->begin_buf(stream, req, &sz, err);
+		gu_assert(sz <= PTRDIFF_MAX);
+		if (buf) {
+			out->buf_end = &buf[sz];
+			out->buf_curr = -(ptrdiff_t) sz;
+			out->buf_size = sz;
+			return true;
+		}
+	}
+	return false;
+}
+
+
+
+static void
+gu_out_fini(GuFinalizer* self)
+{
+	GuOut* out = gu_container(self, GuOut, fini);
+	if (gu_out_is_buffering(out)) {
+		GuPool* pool = gu_local_pool();
+		GuExn* err = gu_new_exn(NULL, gu_kind(type), pool);
+		gu_out_end_buf(out, err);
+		gu_pool_free(pool);
+	}
+}
+
+GuOut*
+gu_new_out(GuOutStream* stream, GuPool* pool)
+{
+	GuOut* out = gu_new(GuOut, pool);
+	*out = gu_init_out(stream);
+	out->fini.fn = gu_out_fini;
+	gu_pool_finally(pool, &out->fini);
+	return out;
+}
+
+extern inline bool
+gu_out_try_buf_(GuOut* out, const uint8_t* src, size_t len);
+
+
+extern inline size_t
+gu_out_bytes(GuOut* out, const uint8_t* buf, size_t len, GuExn* err);
+
+static size_t
+gu_out_output(GuOut* out, const uint8_t* src, size_t len, GuExn* err)
+{
+	gu_out_end_buf(out, err);
+	if (!gu_ok(err)) {
+		return 0;
+	}
+	return out->stream->output(out->stream, src, len, err);
+}
+
+
+
+
+void 
+gu_out_flush(GuOut* out, GuExn* err)
+{
+	GuOutStream* stream = out->stream;
+	if (out->buf_end) {
+		gu_out_end_buf(out, err);
+		if (!gu_ok(err)) {
+			return;
+		}
+	}
+	if (stream->flush) {
+		stream->flush(stream, err);
+	}
+}
+
+uint8_t*
+gu_out_begin_span(GuOut* out, size_t req, size_t* sz_out, GuExn* err)
+{
+	if (!out->buf_end && !gu_out_begin_buf(out, req, err)) {
+		return NULL;
+	}
+	*sz_out = -out->buf_curr;
+	return &out->buf_end[out->buf_curr];
+}
+
+void
+gu_out_end_span(GuOut* out, size_t sz)
+{
+	ptrdiff_t new_curr = (ptrdiff_t) sz + out->buf_curr;
+	gu_require(new_curr <= 0);
+	out->buf_curr = new_curr;
+}
+
+size_t
+gu_out_bytes_(GuOut* restrict out, const uint8_t* restrict src, size_t len, 
+	      GuExn* err)
+{
+	if (!gu_ok(err)) {
+		return 0;
+	} else if (gu_out_try_buf_(out, src, len)) {
+		return len;
+	}
+	if (gu_out_begin_buf(out, len, err)) {
+		if (gu_out_try_buf_(out, src, len)) {
+			return len;
+		}
+	}
+	return gu_out_output(out, src, len, err);
+}
+
+
+void gu_out_u8_(GuOut* restrict out, uint8_t u, GuExn* err)
+{
+	if (gu_out_begin_buf(out, 1, err)) {
+		if (gu_out_try_u8_(out, u)) {
+			return;
+		}
+	}
+	gu_out_output(out, &u, 1, err);
+}
+
+
+extern inline void
+gu_out_u8(GuOut* restrict out, uint8_t u, GuExn* err);
+
+extern inline void
+gu_out_s8(GuOut* restrict out, int8_t i, GuExn* err);
+
+extern inline bool
+gu_out_is_buffered(GuOut* out);
+
+extern inline bool
+gu_out_try_u8_(GuOut* restrict out, uint8_t u);
+
+
+
+
+
+
+
+
+
+typedef struct GuProxyOutStream GuProxyOutStream;
+
+struct GuProxyOutStream {
+	GuOutStream stream;
+	GuOut* real_out;
+};
+
+
+static uint8_t*
+gu_proxy_out_buf_begin(GuOutStream* self, size_t req, size_t* sz_out,
+		       GuExn* err)
+{
+	GuProxyOutStream* pos =
+		gu_container(self, GuProxyOutStream, stream);
+	return gu_out_begin_span(pos->real_out, req, sz_out, err);
+}
+
+static void
+gu_proxy_out_buf_end(GuOutStream* self, size_t sz, GuExn* err)
+{
+	GuProxyOutStream* pos =
+		gu_container(self, GuProxyOutStream, stream);
+	gu_out_end_span(pos->real_out, sz);
+}
+
+static size_t
+gu_proxy_out_output(GuOutStream* self, const uint8_t* src, size_t sz,
+		    GuExn* err)
+{
+	GuProxyOutStream* pos =
+		gu_container(self, GuProxyOutStream, stream);
+	return gu_out_bytes(pos->real_out, src, sz, err);
+}
+
+static void
+gu_proxy_out_flush(GuOutStream* self, GuExn* err)
+{
+	GuProxyOutStream* pos =
+		gu_container(self, GuProxyOutStream, stream);
+	gu_out_flush(pos->real_out, err);
+}
+
+
+GuOutStream*
+gu_out_proxy_stream(GuOut* out, GuPool* pool)
+{
+	return &gu_new_s(pool, GuProxyOutStream,
+			 .stream.begin_buf = gu_proxy_out_buf_begin,
+			 .stream.end_buf = gu_proxy_out_buf_end,
+			 .stream.output = gu_proxy_out_output,
+			 .stream.flush = gu_proxy_out_flush,
+			 .real_out = out)->stream;
+}
+
+
+
+typedef struct GuBufferedOutStream GuBufferedOutStream;
+
+struct GuBufferedOutStream {
+	GuProxyOutStream pstream;
+	size_t sz;
+	uint8_t buf[];
+};
+
+static uint8_t*
+gu_buffered_out_buf_begin(GuOutStream* self, size_t req, size_t* sz_out,
+			  GuExn* err)
+{
+	(void) (req && err);
+	GuBufferedOutStream* b =
+		gu_container(self, GuBufferedOutStream, pstream.stream);
+	*sz_out = b->sz;
+	return b->buf;
+}
+
+static void
+gu_buffered_out_buf_end(GuOutStream* self, size_t sz, GuExn* err)
+{
+	GuBufferedOutStream* b =
+		gu_container(self, GuBufferedOutStream, pstream.stream);
+	gu_require(sz <= b->sz);
+	gu_out_bytes(b->pstream.real_out, b->buf, sz, err);
+}
+
+GuOut*
+gu_new_buffered_out(GuOut* out, size_t sz, GuPool* pool)
+{
+	GuBufferedOutStream* b =
+		gu_new_flex(pool, GuBufferedOutStream, buf, sz);
+	b->pstream.stream = (GuOutStream) {
+		.begin_buf = gu_buffered_out_buf_begin,
+		.end_buf = gu_buffered_out_buf_end,
+		.output = gu_proxy_out_output,
+		.flush = gu_proxy_out_flush
+	};
+	b->pstream.real_out = out;
+	b->sz = sz;
+	return gu_new_out(&b->pstream.stream, pool);
+}
+
+GuOut*
+gu_out_buffered(GuOut* out, GuPool* pool)
+{
+	if (gu_out_is_buffered(out)) {
+		return out;
+	}
+	return gu_new_buffered_out(out, 4096, pool);
+}
+
+
diff --git a/src/runtime/c/gu/out.h b/src/runtime/c/gu/out.h
new file mode 100644
index 000000000..df2638c72
--- /dev/null
+++ b/src/runtime/c/gu/out.h
@@ -0,0 +1,166 @@
+#ifndef GU_OUT_H_
+#define GU_OUT_H_
+
+#include <gu/defs.h>
+#include <gu/assert.h>
+#include <gu/exn.h>
+
+typedef struct GuOut GuOut;
+
+typedef struct GuOutStream GuOutStream;
+
+struct GuOutStream {
+	uint8_t* (*begin_buf)(GuOutStream* self, size_t req, size_t* sz_out,
+			      GuExn* err);
+	void (*end_buf)(GuOutStream* self, size_t span, GuExn* err);
+	size_t (*output)(GuOutStream* self, const uint8_t* buf, size_t size,
+			 GuExn* err);
+	void (*flush)(GuOutStream* self, GuExn* err);
+};
+
+
+struct GuOut {
+	uint8_t* restrict buf_end;
+	ptrdiff_t buf_curr;
+	size_t buf_size;
+	GuOutStream* stream;
+	GuFinalizer fini;
+};
+
+
+GuOut
+gu_init_out(GuOutStream* stream);
+
+GuOut*
+gu_new_out(GuOutStream* stream, GuPool* pool);
+
+inline bool
+gu_out_is_buffered(GuOut* out)
+{
+	return !!out->stream->begin_buf;
+}
+
+GuOutStream*
+gu_out_proxy_stream(GuOut* out, GuPool* pool);
+
+GuOut*
+gu_new_buffered_out(GuOut* out, size_t buf_sz, GuPool* pool);
+
+GuOut*
+gu_out_buffered(GuOut* out, GuPool* pool);
+
+uint8_t*
+gu_out_begin_span(GuOut* out, size_t req, size_t* sz_out, GuExn* err);
+
+uint8_t*
+gu_out_force_span(GuOut* out, size_t min, size_t max, size_t* sz_out,
+		  GuExn* err);
+
+void
+gu_out_end_span(GuOut* out, size_t sz);
+
+size_t
+gu_out_bytes_(GuOut* restrict out, const uint8_t* restrict src, 
+	      size_t len, GuExn* err);
+
+inline bool
+gu_out_try_buf_(GuOut* restrict out, const uint8_t* restrict src, size_t len)
+{
+	gu_require(len <= PTRDIFF_MAX);
+	ptrdiff_t curr = out->buf_curr;
+	ptrdiff_t new_curr = curr + (ptrdiff_t) len;
+	if (GU_UNLIKELY(new_curr > 0)) {
+		return false;
+	}
+	memcpy(&out->buf_end[curr], src, len);
+	out->buf_curr = new_curr;
+	return true;
+}
+
+inline size_t
+gu_out_bytes(GuOut* restrict out, const uint8_t* restrict src, size_t len, 
+	     GuExn* err)
+{
+	if (GU_LIKELY(gu_out_try_buf_(out, src, len))) {
+		return len;
+	}
+	return gu_out_bytes_(out, src, len, err);
+}
+
+void
+gu_out_flush(GuOut* out, GuExn* err);
+
+inline bool
+gu_out_try_u8_(GuOut* restrict out, uint8_t u)
+{
+	ptrdiff_t curr = out->buf_curr;
+	ptrdiff_t new_curr = curr + 1;
+	if (GU_UNLIKELY(new_curr > 0)) {
+		return false;
+	}
+	out->buf_end[curr] = u;
+	out->buf_curr = new_curr;
+	return true;
+}
+
+inline void
+gu_out_u8(GuOut* restrict out, uint8_t u, GuExn* err)
+{
+	if (GU_UNLIKELY(!gu_out_try_u8_(out, u))) {
+		extern void gu_out_u8_(GuOut* restrict out, uint8_t u, 
+				       GuExn* err);
+		gu_out_u8_(out, u, err);
+	}
+}
+
+inline void
+gu_out_s8(GuOut* restrict out, int8_t i, GuExn* err)
+{
+	gu_out_u8(out, (uint8_t) i, err);
+}
+
+
+
+void
+gu_out_u16le(GuOut* out, uint16_t u, GuExn* err);
+
+void
+gu_out_u16be(GuOut* out, uint16_t u, GuExn* err);
+
+void
+gu_out_s16le(GuOut* out, int16_t u, GuExn* err);
+
+void
+gu_out_s16be(GuOut* out, int16_t u, GuExn* err);
+
+void
+gu_out_u32le(GuOut* out, uint32_t u, GuExn* err);
+
+void
+gu_out_u32be(GuOut* out, uint32_t u, GuExn* err);
+
+void
+gu_out_s32le(GuOut* out, int32_t u, GuExn* err);
+
+void
+gu_out_s32be(GuOut* out, int32_t u, GuExn* err);
+
+void
+gu_out_u64le(GuOut* out, uint64_t u, GuExn* err);
+
+void
+gu_out_u64be(GuOut* out, uint64_t u, GuExn* err);
+
+void
+gu_out_s64le(GuOut* out, int64_t u, GuExn* err);
+
+void
+gu_out_s64be(GuOut* out, int64_t u, GuExn* err);
+
+void
+gu_out_f64le(GuOut* out, double d, GuExn* err);
+
+void
+gu_out_f64be(GuOut* out, double d, GuExn* err);
+
+#endif // GU_OUT_H_
diff --git a/src/runtime/c/gu/prime.c b/src/runtime/c/gu/prime.c
new file mode 100644
index 000000000..6452f8777
--- /dev/null
+++ b/src/runtime/c/gu/prime.c
@@ -0,0 +1,154 @@
+#include <gu/defs.h>
+#include <gu/assert.h>
+
+static const uint32_t gu_prime_wheel_mask = 0UL
+	| 1 << 1
+	| 1 << 7
+	| 1 << 11
+	| 1 << 13
+	| 1 << 17
+	| 1 << 19
+	| 1 << 23
+	| 1 << 29;
+
+static bool
+gu_prime_wheel(int i)
+{
+	gu_assert(i >= 0 && i < 30);
+	return !!(gu_prime_wheel_mask & (1 << i));
+}
+
+static const uint32_t gu_small_prime_mask = 0UL
+	| 1 << 2
+	| 1 << 3 
+	| 1 << 5
+	| 1 << 7
+	| 1 << 11
+	| 1 << 13
+	| 1 << 17
+	| 1 << 19
+	| 1 << 23
+	| 1 << 29
+	| 1U << 31;
+
+static bool
+gu_is_wheel_prime(int u)
+{
+	gu_assert(u > 30 && u % 2 != 0 && u % 3 != 0 && u % 5 != 0);
+	int d = 0;
+	int i = 7;
+	goto start;
+	while (d * d <= u) {
+		for (i = 1; i <= 29; i+=2) {
+		start:
+			if (gu_prime_wheel(i) && u % (d + i) == 0) {
+				return false;
+			}
+		}
+		d += 30;
+	}
+	return true;
+}
+
+int
+gu_prime_inf(int i)
+{
+	if (i < 2) {
+		return 0;
+	} else if (i < 32) {
+		while (!(gu_small_prime_mask & (1 << i))) {
+			i--;
+		}
+		return i;
+	}
+
+	int d = (i - 1) | 1;
+	int r = d % 30;
+
+	while (!gu_prime_wheel(r) || !gu_is_wheel_prime(d)) {
+		d -= 2;
+		r -= 2;
+		if (r < 0) {
+			r += 30;
+		} 
+	}
+	return d;
+}
+
+int
+gu_prime_sup(int i)
+{
+	if (i <= 2) {
+		return 2;
+	} else if (i < 32) {
+		while (!(gu_small_prime_mask & (1 << i))) {
+			i++;
+		}
+		return i;
+	}
+
+	int d = i | 1;
+	int r = d % 30;
+
+	while (!gu_prime_wheel(r) || !gu_is_wheel_prime(d)) {
+		d += 2;
+		r += 2;
+		if (r > 30) {
+			r -= 30;
+		}
+	}
+	return d;
+}
+
+bool
+gu_is_prime(int i)
+{
+	if (i < 2) {
+		return false;
+	} else if (i < 30) {
+		return !!(gu_small_prime_mask & (1 << i));
+	} else if (!gu_prime_wheel(i % 30)) {
+		return false;
+	} else {
+		return gu_is_wheel_prime(i);
+	}
+}
+
+bool
+gu_is_twin_prime(int i)
+{
+	return gu_is_prime(i) && gu_is_prime(i - 2);
+}
+
+int
+gu_twin_prime_inf(int i)
+{
+	while (true) {
+		i = gu_prime_inf(i);
+		if (i == 0) {
+			return 0;
+		} else if (gu_is_prime(i - 2)) {
+			return i;
+		}
+		i = i - 4;
+	}
+	return i;
+}
+
+int
+gu_twin_prime_sup(int i)
+{
+	if (i <= 5) {
+		return 5;
+	}
+	i = i - 2;
+	while (true) {
+		i = gu_prime_sup(i);
+		if (gu_is_prime(i + 2)) {
+			return i + 2;
+		}
+		i = i + 4;
+	}
+	return i;
+}
+
diff --git a/src/runtime/c/gu/prime.h b/src/runtime/c/gu/prime.h
new file mode 100644
index 000000000..2ae0617f8
--- /dev/null
+++ b/src/runtime/c/gu/prime.h
@@ -0,0 +1,16 @@
+#ifndef GU_PRIME_H_
+#define GU_PRIME_H_
+
+#include <gu/defs.h>
+
+bool gu_is_prime(int i);
+
+bool gu_is_twin_prime(int i);
+
+int gu_prime_inf(int i);
+int gu_twin_prime_inf(int i);
+
+int gu_prime_sup(int i);
+int gu_twin_prime_sup(int i);
+
+#endif // GU_PRIME_H_
diff --git a/src/runtime/c/gu/read.c b/src/runtime/c/gu/read.c
new file mode 100644
index 000000000..245c59f2c
--- /dev/null
+++ b/src/runtime/c/gu/read.c
@@ -0,0 +1,15 @@
+#include <gu/read.h>
+
+extern inline GuUCS
+gu_read_ucs(GuReader* rdr, GuExn* err);
+
+extern inline char
+gu_getc(GuReader* rdr, GuExn* err);
+
+GuReader*
+gu_new_utf8_reader(GuIn* utf8_in, GuPool* pool)
+{
+	GuReader* rdr = gu_new(GuReader, pool);
+	rdr->in_ = gu_init_in(gu_in_proxy_stream(utf8_in, pool));
+	return rdr;
+}
diff --git a/src/runtime/c/gu/read.h b/src/runtime/c/gu/read.h
new file mode 100644
index 000000000..f2496975d
--- /dev/null
+++ b/src/runtime/c/gu/read.h
@@ -0,0 +1,31 @@
+#ifndef GU_READ_H_
+#define GU_READ_H_
+
+#include <gu/in.h>
+#include <gu/ucs.h>
+#include <gu/utf8.h>
+
+typedef struct GuReader GuReader;
+
+struct GuReader {
+	GuIn in_;
+};
+
+inline GuUCS
+gu_read_ucs(GuReader* rdr, GuExn* err)
+{
+	return gu_in_utf8(&rdr->in_, err);
+}
+
+inline char
+gu_getc(GuReader* rdr, GuExn* err)
+{
+	return gu_in_utf8_char(&rdr->in_, err);
+}
+
+GuReader*
+gu_new_utf8_reader(GuIn* utf8_in, GuPool* pool);
+/**< @todo Implement. */
+   
+
+#endif // GU_READ_H_
diff --git a/src/runtime/c/gu/seq.c b/src/runtime/c/gu/seq.c
new file mode 100644
index 000000000..660cf5af6
--- /dev/null
+++ b/src/runtime/c/gu/seq.c
@@ -0,0 +1,245 @@
+#include <gu/out.h>
+#include <gu/seq.h>
+#include <gu/fun.h>
+#include <gu/assert.h>
+#include <string.h>
+
+
+struct GuBuf {
+	uint8_t* data;
+	size_t elem_size;
+	size_t avail_len;
+	GuFinalizer fin;
+};
+
+GuBuf*
+gu_seq_buf(GuSeq seq)
+{
+	gu_require(gu_tagged_tag(seq.w_) == 0);
+	return gu_word_ptr(seq.w_);
+}
+
+GuSeq
+gu_buf_seq(GuBuf* buf)
+{
+	return (GuSeq) { .w_ = gu_ptr_word(buf) };
+}
+
+size_t
+gu_buf_length(GuBuf* dyn)
+{
+	return (size_t)(((GuWord*)(void*)dyn)[-1] >> 1);
+}
+
+size_t
+gu_buf_avail(GuBuf* buf)
+{
+	return buf->avail_len;
+}
+
+
+static void
+gu_buf_set_length(GuBuf* dyn, size_t new_len)
+{
+	((GuWord*)(void*)dyn)[-1] = ((GuWord) new_len) << 1 | 0x1;
+}
+
+static void
+gu_buf_fini(GuFinalizer* fin)
+{
+	GuBuf* buf = gu_container(fin, GuBuf, fin);
+	gu_mem_buf_free(buf->data);
+}
+
+GuBuf*
+gu_make_buf(size_t elem_size, GuPool* pool)
+{
+	GuBuf* buf = gu_new_prefixed(unsigned, GuBuf, pool);
+	gu_buf_set_length(buf, 0);
+	buf->elem_size = elem_size;
+	buf->data = NULL;
+	buf->avail_len = 0;
+	buf->fin.fn = gu_buf_fini;
+	gu_pool_finally(pool, &buf->fin);
+	gu_buf_set_length(buf, 0);
+	return buf;
+}
+
+static const GuWord gu_empty_seq[2] = {0, 0};
+
+GuSeq
+gu_make_seq(size_t elem_size, size_t length, GuPool* pool)
+{
+	size_t size = elem_size * length;
+	if (0 < length && length <= GU_TAG_MAX) {
+		void* buf = gu_malloc(pool, size);
+		return (GuSeq) { gu_tagged(buf, length) };
+	} else if (size == 0) {
+		return (GuSeq) { gu_tagged((void*)&gu_empty_seq[1], 0) };
+	} else {
+		void* buf = gu_malloc_prefixed(pool,
+					       gu_alignof(GuWord), 
+					       sizeof(GuWord),
+					       0, size);
+		((GuWord*) buf)[-1] = ((GuWord) length) << 1;
+		return (GuSeq) { gu_tagged(buf, 0) };
+	}
+}
+
+static void
+gu_buf_require(GuBuf* buf, size_t req_len)
+{
+	if (req_len <= buf->avail_len) {
+		return;
+	}
+	size_t req_size = buf->elem_size * req_len;
+	size_t real_size;
+	buf->data = gu_mem_buf_realloc(buf->data, req_size,
+				       &real_size);
+	buf->avail_len = real_size / buf->elem_size;
+}
+
+void*
+gu_buf_data(GuBuf* buf)
+{
+	return buf->data;
+}
+
+void*
+gu_buf_extend_n(GuBuf* buf, size_t n_elems)
+{
+	size_t len = gu_buf_length(buf);
+	size_t new_len = len + n_elems;
+	gu_buf_require(buf, new_len);
+	gu_buf_set_length(buf, new_len);
+	return &buf->data[buf->elem_size * len];
+}
+
+void*
+gu_buf_extend(GuBuf* buf)
+{
+	return gu_buf_extend_n(buf, 1);
+}
+
+void
+gu_buf_push_n(GuBuf* buf, const void* data, size_t n_elems)
+{
+	
+	void* p = gu_buf_extend_n(buf, n_elems);
+	memcpy(p, data, buf->elem_size * n_elems);
+}
+
+const void*
+gu_buf_trim_n(GuBuf* buf, size_t n_elems)
+{
+	gu_require(n_elems <= gu_buf_length(buf));
+	size_t new_len = gu_buf_length(buf) - n_elems;
+	gu_buf_set_length(buf, new_len);
+	return &buf->data[buf->elem_size * new_len];
+}
+
+const void*
+gu_buf_trim(GuBuf* buf)
+{
+	return gu_buf_trim_n(buf, 1);
+}
+
+void
+gu_buf_pop_n(GuBuf* buf, size_t n_elems, void* data_out)
+{
+	const void* p = gu_buf_trim_n(buf, n_elems);
+	memcpy(data_out, p, buf->elem_size * n_elems);
+}
+
+GuSeq
+gu_buf_freeze(GuBuf* buf, GuPool* pool)
+{
+	size_t len = gu_buf_length(buf);
+	GuSeq seq = gu_make_seq(buf->elem_size, len, pool);
+	void* bufdata = gu_buf_data(buf);
+	void* seqdata = gu_seq_data(seq);
+	memcpy(seqdata, bufdata, buf->elem_size * len);
+	return seq;
+}
+
+typedef struct GuBufOut GuBufOut;
+struct GuBufOut
+{
+	GuOutStream stream;
+	GuBuf* buf;
+};
+
+static size_t
+gu_buf_out_output(GuOutStream* stream, const uint8_t* src, size_t sz,
+		  GuExn* err)
+{
+	(void) err;
+	GuBufOut* bout = gu_container(stream, GuBufOut, stream);
+	GuBuf* buf = bout->buf;
+	gu_assert(sz % buf->elem_size == 0);
+	size_t len = sz / buf->elem_size;
+	gu_buf_push_n(bout->buf, src, len);
+	return len;
+}
+
+static uint8_t*
+gu_buf_outbuf_begin(GuOutStream* stream, size_t req, size_t* sz_out, GuExn* err)
+{
+	(void) req;
+	(void) err;
+	GuBufOut* bout = gu_container(stream, GuBufOut, stream);
+	GuBuf* buf = bout->buf;
+	size_t esz = buf->elem_size;
+	size_t len = gu_buf_length(buf);
+	gu_buf_require(buf, len + (req + esz - 1) / esz);
+	size_t avail = buf->avail_len;
+	gu_assert(len < avail);
+	*sz_out = esz * (avail - len);
+	return &buf->data[len * esz];
+}
+
+static void
+gu_buf_outbuf_end(GuOutStream* stream, size_t sz, GuExn* err)
+{
+	(void) err;
+	GuBufOut* bout = gu_container(stream, GuBufOut, stream);
+	GuBuf* buf = bout->buf;
+	size_t len = gu_buf_length(buf);
+	size_t elem_size = buf->elem_size;
+	gu_require(sz % elem_size == 0);
+	gu_require(sz < elem_size * (len - buf->avail_len));
+	gu_buf_set_length(buf, len + (sz / elem_size));
+}
+
+GuOut*
+gu_buf_out(GuBuf* buf, GuPool* pool)
+{
+	GuBufOut* bout = gu_new_i(pool, GuBufOut,
+				  .stream.output = gu_buf_out_output,
+				  .stream.begin_buf = gu_buf_outbuf_begin,
+				  .stream.end_buf = gu_buf_outbuf_end,
+				  .buf = buf);
+	return gu_new_out(&bout->stream, pool);
+}
+
+const GuSeq
+gu_null_seq = GU_NULL_SEQ;
+
+
+#include <gu/type.h>
+
+GU_DEFINE_KIND(GuSeq, GuOpaque);
+GU_DEFINE_KIND(GuBuf, abstract);
+
+GU_DEFINE_TYPE(GuChars, GuSeq, gu_type(char));
+GU_DEFINE_TYPE(GuBytes, GuSeq, gu_type(uint8_t));
+
+char*
+gu_chars_str(GuChars chars, GuPool* pool)
+{
+	size_t len = gu_seq_length(chars);
+	char* data = gu_seq_data(chars);
+	char* str = gu_new_str(len, pool);
+	memcpy(str, data, len);
+	return str;
+}
diff --git a/src/runtime/c/gu/seq.h b/src/runtime/c/gu/seq.h
new file mode 100644
index 000000000..257d71e5f
--- /dev/null
+++ b/src/runtime/c/gu/seq.h
@@ -0,0 +1,198 @@
+#ifndef GU_SEQ_H_
+#define GU_SEQ_H_
+
+#include <gu/mem.h>
+#include <gu/bits.h>
+
+
+typedef struct GuBuf GuBuf;
+
+typedef GuOpaque() GuSeq;
+
+GuSeq
+gu_make_seq(size_t elem_size, size_t len, GuPool* pool);
+
+#define gu_new_seq(T, N, POOL)			\
+	gu_make_seq(sizeof(T), (N), (POOL))
+
+static inline size_t
+gu_seq_length(GuSeq seq)
+{
+	GuWord w = seq.w_;
+	size_t tag = gu_tagged_tag(w);
+	if (tag == 0) {
+		GuWord* p = gu_tagged_ptr(w);
+		return (size_t) (p[-1] >> 1);
+	}
+	return tag;
+}
+
+static inline void*
+gu_seq_data(GuSeq seq)
+{
+	GuWord w = seq.w_;
+	int tag = gu_tagged_tag(w);
+	void* ptr = gu_tagged_ptr(w);
+	if (tag == 0) {
+		GuWord* p = ptr;
+		if (p[-1] & 0x1) {
+		 	return *(uint8_t**) ptr;
+		}
+	}
+	return ptr;
+}
+
+static inline bool
+gu_seq_is_null(GuSeq seq)
+{
+	return (gu_tagged_ptr(seq.w_)) == NULL;
+}
+
+
+#define gu_seq_index(SEQ, T, I)			\
+	(&((T*)gu_seq_data(SEQ))[I])
+
+#define gu_seq_get(SEQ, T, I)			\
+	(*gu_seq_index(SEQ, T, I))
+
+#define gu_seq_set(SEQ, T, I, V)			\
+	GU_BEGIN				\
+	(*gu_seq_index(SEQ, T, I) = (V));	\
+	GU_END
+
+
+
+
+GuBuf*
+gu_seq_buf(GuSeq seq);
+
+GuSeq
+gu_buf_seq(GuBuf* buf);
+
+GuBuf*
+gu_make_buf(size_t elem_size, GuPool* pool);
+
+#define gu_new_buf(T, POOL)			\
+	gu_make_buf(sizeof(T), (POOL))
+
+size_t
+gu_buf_length(GuBuf* buf);
+
+size_t
+gu_buf_avail(GuBuf* buf);
+
+void*
+gu_buf_data(GuBuf* buf);
+
+#define gu_buf_index(BUF, T, I)			\
+	(&((T*)gu_buf_data(BUF))[I])
+
+#define gu_buf_get(BUF, T, I)			\
+	(*gu_buf_index(BUF, T, I))
+
+#define gu_buf_set(BUF, T, I)			\
+	GU_BEGIN				\
+	(*gu_buf_index(BUF, T, I) = (V));	\
+	GU_END
+
+void
+gu_buf_push_n(GuBuf* buf, const void* elems, size_t n_elems);
+
+void*
+gu_buf_extend_n(GuBuf* buf, size_t n_elems);
+
+void*
+gu_buf_extend(GuBuf* buf);
+
+#define gu_buf_push(BUF, T, VAL)				\
+	GU_BEGIN						\
+	((*(T*)gu_buf_extend(BUF)) = (VAL));	\
+	GU_END
+
+void
+gu_buf_pop_n(GuBuf* buf, size_t n_elems, void* data_out);
+
+const void*
+gu_buf_trim_n(GuBuf* buf, size_t n_elems);
+
+const void*
+gu_buf_trim(GuBuf* buf);
+
+#define gu_buf_pop(BUF, T)			\
+	(*(T*)gu_buf_trim(BUF))
+
+void
+gu_seq_resize_tail(GuSeq seq, ptrdiff_t change);
+
+#if 0
+void
+gu_buf_resize_head(GuBuf* buf, ptrdiff_t change);
+
+void
+gu_buf_unshift(GuBuf* buf, const void* data, size_t size);
+
+void
+gu_buf_shift(GuBuf* buf, size_t size, void* data_out);
+#endif
+
+GuSeq
+gu_buf_freeze(GuBuf* buf, GuPool* pool);
+
+extern const GuSeq gu_null_seq;
+
+#define GU_NULL_SEQ { .w_ = (GuWord)(void*)NULL }
+
+typedef GuSeq GuChars;
+typedef GuSeq GuBytes;
+typedef GuBuf GuCharBuf;
+typedef GuBuf GuByteBuf;
+
+char*
+gu_chars_str(GuChars chars, GuPool* pool);
+
+#endif // GU_SEQ_H_
+
+#if defined(GU_OUT_H_) && !defined(GU_SEQ_H_OUT_)
+#define GU_SEQ_H_OUT_
+
+GuOut*
+gu_buf_out(GuBuf* buf, GuPool* pool);
+
+#endif
+
+
+#if defined(GU_TYPE_H_) && !defined(GU_SEQ_H_TYPE_)
+#define GU_SEQ_H_TYPE_
+
+extern GU_DECLARE_KIND(GuSeq);
+extern GU_DECLARE_KIND(GuBuf);
+
+struct GuSeqType {
+	GuType_GuOpaque opaque_base;
+	GuType* elem_type;
+};
+
+typedef const struct GuSeqType GuSeqType, GuType_GuSeq;
+
+#define GU_TYPE_INIT_GuSeq(k_, t_, elem_type_) {	   \
+	.opaque_base = GU_TYPE_INIT_GuOpaque(k_, t_, _), \
+	.elem_type = elem_type_,		   	\
+}
+
+typedef struct GuBufType GuBufType, GuType_GuBuf;
+
+struct GuBufType {
+	GuType_abstract abstract_base;
+	GuType* elem_type;
+};
+
+#define GU_TYPE_INIT_GuBuf(KIND, BUF_T, ELEM_T) { \
+	.abstract_base = GU_TYPE_INIT_abstract(KIND, BUF_T, _), \
+	.elem_type = ELEM_T \
+}
+
+extern GU_DECLARE_TYPE(GuChars, GuSeq);
+extern GU_DECLARE_TYPE(GuBytes, GuSeq);
+
+#endif 
+
diff --git a/src/runtime/c/gu/str.c b/src/runtime/c/gu/str.c
new file mode 100644
index 000000000..073781b23
--- /dev/null
+++ b/src/runtime/c/gu/str.c
@@ -0,0 +1,85 @@
+#include <gu/assert.h>
+#include <gu/str.h>
+#include <string.h>
+#include <wchar.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+const char gu_empty_str[] = "";
+const char* const gu_null_str = NULL;
+
+char* 
+gu_new_str(size_t size, GuPool* pool)
+{
+	char* str = gu_new_n(char, size + 1, pool);
+	memset(str, '\0', size + 1);
+	return str;
+}
+
+char*
+gu_strdup(const char* cstr, GuPool* pool)
+{
+	int len = strlen(cstr);
+	char* str = gu_new_str(len, pool);
+	memcpy(str, cstr, len);
+	return str;
+}
+
+bool
+gu_str_eq(GuStr s1, GuStr s2)
+{
+	return (strcmp(s1, s2)) == 0;
+}
+
+static bool
+gu_str_is_equal(GuEquality* self, const void* p1, const void* p2)
+{
+	(void) self;
+	const GuStr* sp1 = p1;
+	const GuStr* sp2 = p2;
+	return gu_str_eq(*sp1, *sp2);
+}
+
+static GuHash
+gu_str_hasher_hash(GuHasher* self, const void* p)
+{
+	(void) self;
+	GuHash h = 0;
+	const GuStr* sp = p;
+	for (const char* s = *sp; *s != '\0'; s++) {
+		h = 101 * h + (unsigned char) *s;
+	}
+	return h;
+}
+
+GuHasher gu_str_hasher[1] = {
+	{
+		.eq = { .is_equal = gu_str_is_equal },
+		.hash = gu_str_hasher_hash
+	}
+};
+
+GU_DEFINE_TYPE(GuStr, repr, _);
+
+char* 
+gu_vasprintf(const char* fmt, va_list args, GuPool* pool)
+{
+	va_list args2;
+	va_copy(args2, args);
+	int len = vsnprintf(NULL, 0, fmt, args2);
+	gu_assert_msg(len >= 0, "Invalid format string: \"%s\"", fmt);
+	va_end(args2);
+	char* str = gu_new_str(len, pool);
+	vsnprintf(str, len + 1, fmt, args);
+	return str;
+}
+
+char* 
+gu_asprintf(GuPool* pool, const char* fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	char* str = gu_vasprintf(fmt, args, pool);
+	va_end(args);
+	return str;
+}
diff --git a/src/runtime/c/gu/str.h b/src/runtime/c/gu/str.h
new file mode 100644
index 000000000..d40f57b08
--- /dev/null
+++ b/src/runtime/c/gu/str.h
@@ -0,0 +1,29 @@
+#ifndef GU_STR_H_
+#define GU_STR_H_
+
+#include <gu/mem.h>
+#include <gu/hash.h>
+
+extern const char gu_empty_str[];
+extern const char* const gu_null_str;
+
+typedef const char* GuStr;
+
+char* gu_new_str(size_t size, GuPool* pool);
+
+char* gu_strdup(const char* str, GuPool* pool);
+
+bool
+gu_str_eq(GuStr s1, GuStr s2);
+
+extern GuHasher gu_str_hasher[1];
+
+#include <gu/type.h>
+
+extern GU_DECLARE_TYPE(GuStr, repr);
+
+char* gu_vasprintf(const char* fmt, va_list args, GuPool* pool);
+
+char* gu_asprintf(GuPool* pool, const char* fmt, ...);
+
+#endif // GU_STR_H_
diff --git a/src/runtime/c/gu/string.c b/src/runtime/c/gu/string.c
new file mode 100644
index 000000000..b24eeeb06
--- /dev/null
+++ b/src/runtime/c/gu/string.c
@@ -0,0 +1,270 @@
+#include <gu/type.h>
+#include <gu/out.h>
+#include <gu/seq.h>
+#include <gu/map.h>
+#include <gu/string.h>
+#include <gu/utf8.h>
+#include <gu/assert.h>
+#include "config.h"
+
+const GuString gu_empty_string = { 1 };
+
+struct GuStringBuf {
+	GuByteBuf* bbuf;
+	GuWriter* wtr;
+};
+
+GuStringBuf*
+gu_string_buf(GuPool* pool)
+{
+	GuBuf* buf = gu_new_buf(uint8_t, pool);
+	GuOut* out = gu_buf_out(buf, pool);
+	GuWriter* wtr = gu_new_utf8_writer(out, pool);
+	return gu_new_s(pool, GuStringBuf,
+			.bbuf = buf,
+			.wtr = wtr);
+}
+
+GuWriter*
+gu_string_buf_writer(GuStringBuf* sb)
+{
+	return sb->wtr;
+}
+
+static GuString
+gu_utf8_string(const uint8_t* buf, size_t sz, GuPool* pool)
+{
+	if (sz < GU_MIN(sizeof(GuWord), 128)) {
+		GuWord w = 0;
+		for (size_t n = 0; n < sz; n++) {
+			w = w << 8 | buf[n];
+		}
+		w = w << 8 | (sz << 1) | 1;
+		return (GuString) { w };
+	}
+	uint8_t* p = NULL;
+	if (sz < 256) {
+		p = gu_malloc_aligned(pool, 1 + sz, 2);
+		p[0] = (uint8_t) sz;
+	} else {
+		uint8_t* p =
+			gu_malloc_prefixed(pool, gu_alignof(size_t),
+					   sizeof(size_t), 1, 1 + sizeof(sz));
+		((size_t*) p)[-1] = sz;
+		p[0] = 0;
+	}
+	memcpy(&p[1], buf, sz);
+	return (GuString) { (GuWord) (void*) p };
+}
+
+
+
+GuString
+gu_string_buf_freeze(GuStringBuf* sb, GuPool* pool)
+{
+	gu_writer_flush(sb->wtr, NULL);
+	uint8_t* data = gu_buf_data(sb->bbuf);
+	size_t len = gu_buf_length(sb->bbuf);
+	return gu_utf8_string(data, len, pool);
+}
+
+GuReader*
+gu_string_reader(GuString s, GuPool* pool)
+{
+	GuWord w = s.w_;
+	uint8_t* buf = NULL;
+	size_t len = 0;
+	if (w & 1) {
+		len = (w & 0xff) >> 1;
+		buf = gu_new_n(uint8_t, len, pool);
+		for (int i = len - 1; i >= 0; i--) {
+			w >>= 8;
+			buf[i] = w & 0xff;
+		}
+	} else {
+		uint8_t* p = (void*) w;
+		len = (p[0] == 0) ? ((size_t*) p)[-1] : p[0];
+		buf = &p[1];
+	}
+	GuIn* in = gu_data_in(buf, len, pool);
+	GuReader* rdr = gu_new_utf8_reader(in, pool);
+	return rdr;
+}
+
+static bool
+gu_string_is_long(GuString s) 
+{
+	return !(s.w_ & 1);
+}
+
+bool
+gu_string_is_stable(GuString s)
+{
+	return !gu_string_is_long(s);
+}
+
+static size_t
+gu_string_long_length(GuString s)
+{
+	gu_assert(gu_string_is_long(s));
+	uint8_t* p = (void*) s.w_;
+	uint8_t len = p[0];
+	if (len > 0) {
+		return len;
+	}
+	return ((size_t*) p)[-1];
+}
+
+size_t
+gu_string_length(GuString s)
+{
+	if (gu_string_is_long(s)) {
+		return gu_string_long_length(s);
+	}
+	return (s.w_ & 0xff) >> 1;
+}
+
+static uint8_t*
+gu_string_long_data(GuString s)
+{
+	gu_require(gu_string_is_long(s));
+	uint8_t* p = (void*) s.w_;
+	return &p[1];
+}
+
+GuString
+gu_string_copy(GuString string, GuPool* pool)
+{
+	if (gu_string_is_long(string)) {
+		uint8_t* data = gu_string_long_data(string);
+		size_t len = gu_string_long_length(string);
+		return gu_utf8_string(data, len, pool);
+	} else {
+		return string;
+	}
+}
+
+
+void
+gu_string_write(GuString s, GuWriter* wtr, GuExn* err)
+{
+	GuWord w = s.w_;
+	uint8_t buf[sizeof(GuWord)];
+	uint8_t* src;
+	size_t sz;
+	if (w & 1) {
+		sz = (w & 0xff) >> 1;
+		gu_assert(sz <= sizeof(GuWord));
+		size_t i = sz;
+		while (i > 0) {
+			w >>= 8;
+			buf[--i] = w & 0xff;
+		}
+		src = buf;
+	} else {
+		uint8_t* p = (void*) w;
+		sz = (p[0] == 0) ? ((size_t*) p)[-1] : p[0];
+		src = &p[1];
+	}
+	gu_utf8_write(src, sz, wtr, err);
+}
+
+GuString
+gu_format_string_v(const char* fmt, va_list args, GuPool* pool)
+{
+	GuPool* tmp_pool = gu_local_pool();
+	GuStringBuf* sb = gu_string_buf(tmp_pool);
+	GuWriter* wtr = gu_string_buf_writer(sb);
+	gu_vprintf(fmt, args, wtr, NULL);
+	gu_writer_flush(wtr, NULL);
+	GuString s = gu_string_buf_freeze(sb, pool);
+	gu_pool_free(tmp_pool);
+	return s;
+}
+
+GuString
+gu_format_string(GuPool* pool, const char* fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	GuString s = gu_format_string_v(fmt, args, pool);
+	va_end(args);
+	return s;
+}
+
+GuString
+gu_str_string(const char* str, GuPool* pool)
+{
+#ifdef GU_CHAR_ASCII
+	return gu_utf8_string((const uint8_t*) str, strlen(str), pool);
+#else
+	GuPool* tmp_pool = gu_local_pool();
+	GuStringBuf* sb = gu_string_buf(tmp_pool);
+	GuWriter* wtr = gu_string_buf_writer(sb);
+	gu_puts(str, wtr, NULL);
+	gu_writer_flush(wtr, NULL);
+	GuString s = gu_string_buf_freeze(sb, pool);
+	gu_pool_free(tmp_pool);
+	return s;
+#endif
+}
+
+GuWord
+gu_string_hash(GuString s)
+{
+	if (s.w_ & 1) {
+		return s.w_;
+	}
+	size_t len = gu_string_length(s);
+	uint8_t* data = gu_string_long_data(s);
+	return gu_hash_bytes(0, data, len);
+}
+
+bool
+gu_string_eq(GuString s1, GuString s2)
+{
+	if (s1.w_ == s2.w_) {
+		return true;
+	} else if (gu_string_is_long(s1) && gu_string_is_long(s2)) {
+		size_t len1 = gu_string_long_length(s1);
+		size_t len2 = gu_string_long_length(s2);
+		if (len1 != len2) {
+			return false;
+		}
+		uint8_t* data1 = gu_string_long_data(s1);
+		uint8_t* data2 = gu_string_long_data(s2);
+		return (memcmp(data1, data2, len1) == 0);
+	}
+	return false;
+
+}
+
+
+static GuHash
+gu_string_hasher_hash(GuHasher* self, const void* p)
+{
+	(void) self;
+	const GuString* sp = p;
+	return gu_string_hash(*sp);
+}
+
+static bool
+gu_string_eq_fn(GuEquality* self, const void* p1, const void* p2)
+{
+	(void) self;
+	const GuString* sp1 = p1;
+	const GuString* sp2 = p2;
+	return gu_string_eq(*sp1, *sp2);
+}
+
+GuHasher gu_string_hasher[1] = {
+	{
+		.eq = { gu_string_eq_fn },
+		.hash = gu_string_hasher_hash
+	}
+};
+
+
+GU_DEFINE_TYPE(GuString, GuOpaque, _);
+GU_DEFINE_TYPE(GuStrings, GuSeq, gu_type(GuString));
+GU_DEFINE_KIND(GuStringMap, GuMap);
diff --git a/src/runtime/c/gu/string.h b/src/runtime/c/gu/string.h
new file mode 100644
index 000000000..385b162ed
--- /dev/null
+++ b/src/runtime/c/gu/string.h
@@ -0,0 +1,125 @@
+/* 
+ * Copyright 2011 University of Helsinki.
+ *   
+ * This file is part of libgu.
+ * 
+ * Libgu is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ * 
+ * Libgu is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with libgu. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef GU_STRING_H_
+#define GU_STRING_H_
+
+#include <gu/bits.h>
+#include <gu/read.h>
+#include <gu/write.h>
+
+typedef GuOpaque() GuString;
+
+extern const GuString gu_empty_string;
+
+GuString
+gu_string_copy(GuString string, GuPool* pool);
+
+void
+gu_string_write(GuString string, GuWriter* wtr, GuExn* err);
+
+GuReader*
+gu_string_reader(GuString string, GuPool* pool);
+
+bool
+gu_string_is_stable(GuString string);
+
+GuString
+gu_ucs_string(const GuUCS* ubuf, size_t len, GuPool* pool);
+
+typedef struct GuStringBuf GuStringBuf;
+
+GuStringBuf*
+gu_string_buf(GuPool* pool);
+
+GuWriter*
+gu_string_buf_writer(GuStringBuf* sb);
+
+GuString
+gu_string_buf_freeze(GuStringBuf* sb, GuPool* pool);
+
+GuString
+gu_format_string_v(const char* fmt, va_list args, GuPool* pool);
+
+GuString
+gu_format_string(GuPool* pool, const char* fmt, ...);
+
+GuString
+gu_str_string(const char* str, GuPool* pool);
+
+#endif // GU_STRING_H_
+
+#if defined(GU_HASH_H_) && !defined(GU_STRING_H_HASH_)
+#define GU_STRING_H_HASH_
+
+uintptr_t
+gu_string_hash(GuString s);
+
+extern GuHasher gu_string_hasher[1];
+
+bool
+gu_string_eq(GuString s1, GuString s2);
+#endif
+
+#ifdef GU_TYPE_H_
+# ifndef GU_STRING_H_TYPE_
+#  define GU_STRING_H_TYPE_
+
+extern GU_DECLARE_TYPE(GuString, GuOpaque);
+# endif
+
+# if defined(GU_SEQ_H_) && !defined(GU_STRING_H_SEQ_TYPE_)
+#  define GU_STRING_H_SEQ_TYPE_
+extern GU_DECLARE_TYPE(GuStrings, GuSeq);
+# endif
+
+# if defined(GU_MAP_H_TYPE_) && !defined(GU_STRING_H_MAP_TYPE_)
+#  define GU_STRING_H_MAP_TYPE_
+
+extern GU_DECLARE_KIND(GuStringMap);
+typedef GuType_GuMap GuType_GuStringMap;
+
+#define GU_TYPE_INIT_GuStringMap(KIND, MAP_T, VAL_T, DEFAULT)	\
+	GU_TYPE_INIT_GuMap(KIND, MAP_T,				\
+			   gu_type(GuString), gu_string_hasher,	\
+			   VAL_T, DEFAULT)
+
+# endif
+#endif
+
+
+#if defined(GU_SEQ_H_) && !defined(GU_STRING_H_SEQ_)
+#define GU_STRING_H_SEQ_
+
+typedef GuSeq GuStrings;
+// typedef GuBuf GuStringBuf;
+
+#endif
+
+
+#if defined(GU_MAP_H_) && !defined(GU_STRING_H_MAP_)
+#define GU_STRING_H_MAP_
+
+typedef GuMap GuStringMap;
+
+#define gu_new_string_map(VAL_T, DEFAULT, POOL)				\
+	gu_new_map(GuString, gu_string_hasher, (VAL_T), (DEFAULT), (POOL))
+
+#endif
+
diff --git a/src/runtime/c/gu/sysdeps.h b/src/runtime/c/gu/sysdeps.h
new file mode 100644
index 000000000..114e1c40d
--- /dev/null
+++ b/src/runtime/c/gu/sysdeps.h
@@ -0,0 +1,30 @@
+#ifndef GU_SYSDEPS_H_
+#define GU_SYSDEPS_H_
+
+#include <guconfig.h>
+
+#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
+# define GU_GNUC
+#endif
+
+#ifdef GU_GNUC
+# define GU_ALIGNOF __alignof
+# define GU_HAVE_STATEMENT_EXPRESSIONS
+# define GU_GNUC_ATTR(x) __attribute__(( x ))
+# if defined(__OPTIMIZE_SIZE__)
+#  define GU_OPTIMIZE_SIZE
+# elif defined(__OPTIMIZE__)
+#  define GU_OPTIMIZE_SPEED
+# endif
+#else
+# define GU_GNUC_ATTR(x)
+#endif
+
+#ifdef S_SPLINT_S
+# define GU_SPLINT(x) %{ x %}
+#else
+# define GU_SPLINT(x)
+#endif
+
+
+#endif // GU_SYSDEPS_H_
diff --git a/src/runtime/c/gu/type.c b/src/runtime/c/gu/type.c
new file mode 100644
index 000000000..13fbfa42d
--- /dev/null
+++ b/src/runtime/c/gu/type.c
@@ -0,0 +1,229 @@
+
+#include <gu/type.h>
+#include <gu/assert.h>
+#include <gu/map.h>
+
+GuKind GU_TYPE_IDENT(type)[1] = {{ .super = NULL }};
+
+GU_DEFINE_KIND(alias, type);
+GU_DEFINE_KIND(typedef, alias);
+GU_DEFINE_KIND(referenced, alias);
+
+GU_DEFINE_KIND(repr, type);
+GU_DEFINE_KIND(GuOpaque, repr);
+
+GU_DEFINE_KIND(abstract, type);
+
+GU_DEFINE_KIND(struct, repr);
+
+GU_DEFINE_KIND(pointer, repr);
+GU_DEFINE_KIND(reference, pointer);
+GU_DEFINE_KIND(shared, pointer);
+
+GU_DEFINE_KIND(primitive, repr);
+
+// sizeof(void) is illegal, so do this manually
+GuPrimType GU_TYPE_IDENT(void)[1] = {{
+	.repr_base = {
+		.type_base = {
+			.kind_base = {
+				.super = gu_kind(primitive),
+			},
+		},
+		.size = 0,
+		.align = 1,
+	},
+	.name = "void",
+}};
+
+GU_DEFINE_KIND(integer, primitive);
+GU_DEFINE_TYPE(char, integer, _);
+
+GU_DEFINE_KIND(signed, integer);
+GU_DEFINE_TYPE(int, signed, _);
+GU_DEFINE_TYPE(int8_t, signed, _);
+GU_DEFINE_TYPE(int16_t, signed, _);
+GU_DEFINE_TYPE(int32_t, signed, _);
+GU_DEFINE_TYPE(int64_t, signed, _);
+GU_DEFINE_TYPE(intptr_t, signed, _);
+GU_DEFINE_TYPE(intmax_t, signed, _);
+
+GU_DEFINE_KIND(unsigned, integer);
+GU_DEFINE_TYPE(uint8_t, unsigned, _);
+GU_DEFINE_TYPE(uint16_t, unsigned, _);
+GU_DEFINE_TYPE(uint32_t, unsigned, _);
+GU_DEFINE_TYPE(uint64_t, unsigned, _);
+GU_DEFINE_TYPE(uintmax_t, unsigned, _);
+GU_DEFINE_TYPE(size_t, unsigned, _);
+
+GU_DEFINE_TYPE(GuLength, unsigned, _);
+
+GU_DEFINE_KIND(GuFloating, primitive);
+GU_DEFINE_TYPE(float, GuFloating, _);
+GU_DEFINE_TYPE(double, GuFloating, _);
+GU_DEFINE_TYPE(GuLongDouble, GuFloating, _);
+
+
+GU_DEFINE_KIND(enum, repr);
+
+bool gu_type_has_kind(GuType* type, GuKind* kind)
+{
+	GuKind* k = (GuKind*)type;
+	while (k != NULL) {
+		if (k == kind) {
+			return true;
+		}
+		k = k->super;
+	}
+	return false;
+}
+
+
+struct GuTypeMap {
+	GuMap* map;
+};
+
+static void
+gu_type_map_init(GuTypeMap* tmap, GuTypeTable* table) 
+{
+	for (int i = 0; i < table->parents.len; i++) {
+		gu_type_map_init(tmap, table->parents.elems[i]);
+	}
+	for (int i = 0; i < table->entries.len; i++) {
+		GuTypeTableEntry* e = &table->entries.elems[i];
+		gu_map_put(tmap->map, e->kind, void*, e->val);
+	}
+}
+
+GuTypeMap*
+gu_new_type_map(GuTypeTable* table, GuPool* pool)
+{
+	GuTypeMap* tmap =
+		gu_new_i(pool, GuTypeMap,
+			 .map = gu_new_map(GuKind, NULL, void*, &gu_null, pool));
+	gu_type_map_init(tmap, table);
+	return tmap;
+}
+
+bool
+gu_struct_has_flex(GuStructRepr* srepr)
+{
+	for (int i = 0; i < srepr->members.len; i++) {
+		if (srepr->members.elems[i].is_flex) {
+			return true;
+		}
+	}
+	return false;
+}
+
+void*
+gu_type_map_get(GuTypeMap* tmap, GuType* type)
+{
+	GuKind* kind = (GuKind*)type;
+	while (kind != NULL) {
+		void* val = gu_map_get(tmap->map, kind, void*);
+		if (val != NULL) {
+			return val;
+		}
+		kind = kind->super;
+	}
+	return NULL;
+}
+
+const void*
+gu_type_dyn_cast(GuType* type, GuKind* kind)
+{
+	if (gu_type_has_kind(type, kind)) {
+		return type;
+	}
+	return NULL;
+}
+
+
+const void* 
+gu_type_check_cast(GuType* type, GuKind* kind)
+{
+	gu_assert(gu_type_has_kind(type, kind));
+	return type;
+}
+
+GuTypeRepr*
+gu_type_repr(GuType* type) 
+{
+	GuTypeAlias* alias;
+	while ((alias = gu_type_try_cast(type, alias))) {
+		type = alias->type;
+	}
+	return gu_type_try_cast(type, repr);
+}
+
+size_t
+gu_type_size(GuType* type)
+{
+	GuTypeRepr* repr = gu_type_repr(type);
+	return repr ? repr->size : 0;
+}
+
+GuEnumConstant*
+gu_enum_value(GuEnumType* etype, const void* enump)
+{
+	size_t esize = etype->repr_base.size;
+#define CHECK_ENUM_TYPE(t_) do {					\
+		if (esize == sizeof(t_)) {				\
+			t_ c = *(const t_*)enump;			\
+			for (int i = 0; i < etype->constants.len; i++) { \
+				GuEnumConstant* cp = &etype->constants.elems[i]; \
+				t_ d = *(const t_*)cp->enum_value;	\
+				if (c == d) {				\
+					return cp;			\
+				}					\
+			}						\
+			return NULL;					\
+		}							\
+	} while (false)
+
+	CHECK_ENUM_TYPE(int);
+	CHECK_ENUM_TYPE(char);
+	CHECK_ENUM_TYPE(short);
+	CHECK_ENUM_TYPE(long);
+	CHECK_ENUM_TYPE(long long);
+
+	return NULL;
+}
+
+void*
+gu_type_malloc(GuType* type, GuPool* pool)
+{
+	GuTypeRepr* repr = gu_type_repr(type);
+	gu_assert(repr);
+	return gu_malloc_aligned(pool, repr->size, repr->align);
+}
+
+#if 0
+
+typedef const struct GuPtrConvFns GuPtrConvFns;
+
+struct GuPtrConvFns {
+	void* (*get)(const void* pp);
+	void (*set)(void** pp, void* p);
+};
+
+#define GU_TYPE_PTR_DEFINE_GETSET(name_, t_)				\
+	static void* gu_type_##name_##_ptr_get(const void* pp) {	\
+		return *(t_* const*) pp;				\
+	}								\
+									\
+	static void gu_type_##name_##_ptr_set(void* pp, void* p) {	\
+		*(t_**) pp = p;						\
+	}								\
+	static GuPtrConvFns gu_ptr_conv_##name_ = {			\
+		.get = gu_type_##name_##_ptr_get,			\
+		.set = gu_type_##name_##_ptr_set			\
+	}
+
+GU_TYPE_PTR_DEFINE_GETSET(void, void);
+GU_TYPE_PTR_DEFINE_GETSET(struct, GuStruct);
+GU_TYPE_PTR_DEFINE_GETSET(int, int);
+
+
+#endif
diff --git a/src/runtime/c/gu/type.h b/src/runtime/c/gu/type.h
new file mode 100644
index 000000000..777b2e1f9
--- /dev/null
+++ b/src/runtime/c/gu/type.h
@@ -0,0 +1,454 @@
+ 
+#ifndef GU_TYPE_H_
+#define GU_TYPE_H_
+
+#include <gu/defs.h>
+
+//
+// kind
+//
+
+typedef const struct GuKind GuKind;
+
+struct GuKind {
+	GuKind* super;
+};
+
+// Use GU_PASTE here so k_ can be preprocessor-expanded
+#define GU_TYPE_IDENT(k_) GU_PASTE(gu_type__,k_)
+
+#define gu_kind(k_) ((GuKind*)GU_TYPE_IDENT(k_))
+
+#define GU_DECLARE_KIND(k_) \
+	GuKind GU_TYPE_IDENT(k_)[1]
+
+extern GU_DECLARE_KIND(kind);
+
+#define GU_DEFINE_KIND(k_, super_k_) \
+	GuKind GU_TYPE_IDENT(k_)[1] = {{ .super = gu_kind(super_k_) }}
+
+//
+// type
+//
+
+typedef const struct GuType GuType;
+
+struct GuType {
+	GuKind kind_base;
+};
+
+typedef GuType GuType_type;
+
+extern GU_DECLARE_KIND(type);
+
+#define GU_TYPE_INIT_type(k_, t_, _) { .kind_base = { .super = gu_kind(k_) } }
+
+#define gu_type(t_) ((GuType*)gu_kind(t_))
+
+
+#define GU_KIND_TYPE(k_) GU_PASTE(GuType_,k_)
+
+// This cannot be used indirectly, since we don't want to pp-expand k_.
+// We must inline the body into other macros.
+#define GU_TYPE_INIT(k_, ...)		\
+	GU_TYPE_INIT_##k_(k_, __VA_ARGS__)
+
+//#define GU_TYPE_LIT(k_, ...)						
+//	((GuType*)(GuType_##k_[]){GU_TYPE_INIT(k_, __VA_ARGS__)})
+#define GU_TYPE_LIT(k_, ...)						\
+	((GuType*)&(GU_KIND_TYPE(k_)) GU_TYPE_INIT_##k_(k_, __VA_ARGS__))
+
+#define GU_DECLARE_TYPE(t_, k_)	\
+	GU_KIND_TYPE(k_) GU_TYPE_IDENT(t_)[1]
+
+//#define GU_DEFINE_TYPE(t_, k_, ...)					
+//	GuType_##k_ GU_TYPE_IDENT(t_) = GU_TYPE_INIT(k_, t_, __VA_ARGS__)
+#define GU_DEFINE_TYPE(t_, k_, ...)					\
+	GU_KIND_TYPE(k_) GU_TYPE_IDENT(t_)[1] =				\
+	{ GU_TYPE_INIT_##k_(k_, t_, __VA_ARGS__) }
+
+#define GU_DEFINE_TYPE_ALIAS(t1_, t2_)		\
+	static GuType* const GU_TYPE_IDENT(t1_) = gu_type(t2_)
+
+
+//
+// abstract
+//
+
+typedef GuType GuType_abstract;
+
+#define GU_TYPE_INIT_abstract(k_, t_, _)		\
+	GU_TYPE_INIT_type(k_, t_, _)
+
+extern GU_DECLARE_KIND(abstract);
+
+
+//
+// repr 
+//
+
+typedef struct GuTypeRepr GuTypeRepr, GuType_repr;
+
+struct GuTypeRepr {
+	GuType type_base;
+	uint16_t size;
+	uint16_t align;
+};
+
+#define GU_TYPE_INIT_repr(k_, t_, _) {				\
+		.type_base = GU_TYPE_INIT_type(k_, t_, _),	\
+		.size = sizeof(t_), \
+		.align = gu_alignof(t_) \
+		 }
+
+extern GU_DECLARE_KIND(repr);
+
+
+
+//
+// GuOpaque
+//
+
+typedef GuType_repr GuType_GuOpaque;
+
+#define GU_TYPE_INIT_GuOpaque GU_TYPE_INIT_repr
+
+extern GU_DECLARE_KIND(GuOpaque);
+
+//
+// pointer
+//
+
+typedef const struct GuPointerType GuPointerType, GuType_pointer;
+
+struct GuPointerType {
+	GuType_repr repr_base;
+	GuType* pointed_type;
+};
+
+#define GU_TYPE_INIT_pointer(k_, t_, pointed_)	\
+	{					   \
+		.repr_base = GU_TYPE_INIT_repr(k_, t_, _),	\
+	.pointed_type = pointed_ \
+}	
+
+
+extern GU_DECLARE_KIND(pointer);
+
+#define gu_ptr_type(t_) \
+	GU_TYPE_LIT(pointer, t_*, gu_type(t_))
+
+
+
+
+
+
+
+//
+// alias
+//
+
+
+typedef const struct GuTypeAlias GuTypeAlias, GuType_alias;
+
+struct GuTypeAlias {
+	GuType type_base;
+	GuType* type;
+};
+
+#define GU_TYPE_INIT_alias(k_, t_, type_) {			\
+	.type_base = GU_TYPE_INIT_type(k_, t_, _),	\
+	.type = type_				\
+}
+
+extern GU_DECLARE_KIND(alias);
+
+//
+// typedef
+//
+
+typedef const struct GuTypeDef GuTypeDef, GuType_typedef;
+
+struct GuTypeDef {
+        GuType_alias alias_base;
+	const char* name;
+};
+
+#define GU_TYPE_INIT_typedef(k_, t_, type_) {			\
+	.alias_base = GU_TYPE_INIT_alias(k_, t_, type_),	\
+	.name = #t_,		\
+}
+
+extern GU_DECLARE_KIND(typedef);
+
+#define GU_DEFINE_TYPEDEF_X(t_, dk_, k_, ...)			\
+	GU_DEFINE_TYPE(t_, dk_, GU_TYPE_LIT(k_, t_, __VA_ARGS__))
+
+#define GU_DEFINE_TYPEDEF(t_, ...)	\
+	GU_DEFINE_TYPEDEF_X(t_, typedef, __VA_ARGS__)
+
+
+
+//
+// referenced
+//
+
+extern GU_DECLARE_KIND(referenced);
+
+typedef GuType_alias GuType_referenced;
+
+#define GU_TYPE_INIT_referenced GU_TYPE_INIT_alias
+
+
+
+#include <gu/list.h>
+
+//
+// struct
+//
+
+typedef const struct GuStructRepr GuStructRepr, GuType_struct;
+
+typedef const struct GuMember GuMember;
+
+struct GuMember {
+	ptrdiff_t offset;
+	const char* name;
+	GuType* type;
+	bool is_flex;
+};
+
+struct GuStructRepr {
+	GuType_repr repr_base;
+	const char* name;
+	GuSList(GuMember) members;
+};
+
+extern GU_DECLARE_KIND(struct);
+
+#define GU_MEMBER_AUX_(struct_, member_, type_, is_flex_)      \
+	{					      \
+		.offset = offsetof(struct_, member_), \
+		.name = #member_,	      \
+		.type = type_,		      \
+		.is_flex = is_flex_,  \
+	}
+
+#define GU_MEMBER_V(struct_, member_, type_) \
+	GU_MEMBER_AUX_(struct_, member_, type_, false)
+
+#define GU_MEMBER(s_, m_, t_) \
+	GU_MEMBER_V(s_, m_, gu_type(t_))
+
+#define GU_MEMBER_P(s_, m_, t_) \
+	GU_MEMBER_V(s_, m_, gu_ptr_type(t_))
+
+#define GU_MEMBER_S(s_, m_, t_) \
+	GU_MEMBER_V(s_, m_, gu_shared_ptr_type(t_))
+
+#define GU_FLEX_MEMBER_V(struct_, member_, type_) \
+	GU_MEMBER_AUX_(struct_, member_, type_, true)
+
+#define GU_FLEX_MEMBER(s_, m_, t_) \
+	GU_FLEX_MEMBER_V(s_, m_, gu_type(t_))
+
+#define GU_FLEX_MEMBER_P(s_, m_, t_) \
+	GU_FLEX_MEMBER_V(s_, m_, gu_ptr_type(t_))
+
+
+#define GU_TYPE_INIT_struct(k_, t_, ...)	{		\
+	.repr_base = GU_TYPE_INIT_repr(k_, t_, _),		\
+	.name = #t_, \
+	.members = GU_SLIST(GuMember, __VA_ARGS__)	\
+}
+
+bool
+gu_struct_has_flex(GuStructRepr* srepr);
+
+
+//
+// reference
+//
+
+typedef GuType_pointer GuType_reference;
+
+#define GU_TYPE_INIT_reference GU_TYPE_INIT_pointer
+
+extern GU_DECLARE_KIND(reference);
+
+
+//
+// shared
+//
+
+typedef GuType_pointer GuType_shared;
+
+#define GU_TYPE_INIT_shared GU_TYPE_INIT_pointer
+
+extern GU_DECLARE_KIND(shared);
+
+#define gu_shared_ptr_type(t_) \
+	GU_TYPE_LIT(shared, t_*, gu_type(t_))
+
+//
+// primitives
+//
+
+typedef const struct GuPrimType GuPrimType, GuType_primitive;
+
+struct GuPrimType {
+	GuType_repr repr_base;
+	const char* name;
+};
+
+#define GU_TYPE_INIT_primitive(k_, t_, _) {	\
+	.repr_base = GU_TYPE_INIT_repr(k_, t_, _),	\
+	.name = #t_			\
+}	
+
+extern GU_DECLARE_KIND(primitive);
+extern GU_DECLARE_TYPE(void, primitive);
+
+#define GU_TYPE_INIT_integer GU_TYPE_INIT_primitive
+typedef GuType_primitive GuType_integer;
+extern GU_DECLARE_KIND(integer);
+extern GU_DECLARE_TYPE(char, integer);
+
+#define GU_TYPE_INIT_signed GU_TYPE_INIT_integer
+typedef GuType_integer GuType_signed;
+extern GU_DECLARE_KIND(signed);
+extern GU_DECLARE_TYPE(int, signed);
+extern GU_DECLARE_TYPE(int8_t, signed);
+extern GU_DECLARE_TYPE(int16_t, signed);
+extern GU_DECLARE_TYPE(int32_t, signed);
+extern GU_DECLARE_TYPE(int64_t, signed);
+extern GU_DECLARE_TYPE(intptr_t, signed);
+extern GU_DECLARE_TYPE(intmax_t, signed);
+
+#define GU_TYPE_INIT_unsigned GU_TYPE_INIT_integer
+typedef GuType_integer GuType_unsigned;
+extern GU_DECLARE_KIND(unsigned);
+extern GU_DECLARE_TYPE(uint8_t, unsigned);
+extern GU_DECLARE_TYPE(uint16_t, unsigned);
+extern GU_DECLARE_TYPE(uint32_t, unsigned);
+extern GU_DECLARE_TYPE(uint64_t, unsigned);
+extern GU_DECLARE_TYPE(uintmax_t, unsigned);
+extern GU_DECLARE_TYPE(size_t, unsigned);
+
+typedef size_t GuLength;
+extern GU_DECLARE_TYPE(GuLength, unsigned); // TODO: get rid
+
+
+#define GU_TYPE_INIT_GuFloating GU_TYPE_INIT_primitive
+typedef GuType_primitive GuType_GuFloating;
+extern GU_DECLARE_KIND(GuFloating);
+extern GU_DECLARE_TYPE(float, GuFloating);
+extern GU_DECLARE_TYPE(double, GuFloating);
+typedef long double GuLongDouble;
+extern GU_DECLARE_TYPE(GuLongDouble, GuFloating);
+
+
+
+//
+// enum
+//
+
+extern GU_DECLARE_KIND(enum);
+
+typedef const struct GuEnumConstant GuEnumConstant;
+
+struct GuEnumConstant {
+	const char* name;
+	int64_t value;
+	const void* enum_value;
+};
+
+typedef const struct GuEnumType GuEnumType, GuType_enum;
+
+struct GuEnumType {
+	GuType_repr repr_base;
+	GuSList(GuEnumConstant) constants;
+};
+
+#define GU_ENUM_C(t_, x) {		\
+		.name = #x, \
+		.value = x,		\
+		.enum_value = (const t_[1]){ x } \
+ }
+
+#define GU_TYPE_INIT_enum(k_, t_, ...) { \
+	.repr_base = GU_TYPE_INIT_repr(k_, t_, _),	\
+	.constants = GU_SLIST(GuEnumConstant, __VA_ARGS__) \
+}
+
+GuEnumConstant*
+gu_enum_value(GuEnumType* etype, const void* enump);
+
+
+
+
+bool gu_type_has_kind(const GuType* type, const GuKind* kind);
+
+
+
+
+typedef const struct GuTypeTableEntry GuTypeTableEntry;
+
+struct GuTypeTableEntry {
+	GuKind* kind;
+	void* val;
+};
+
+typedef const struct GuTypeTable GuTypeTable;
+
+struct GuTypeTable {
+	GuSList(const GuTypeTable*) parents;
+	GuSList(GuTypeTableEntry) entries;
+};
+
+#define GU_TYPETABLE(parents_, ...) { \
+	.parents = parents_, \
+	.entries = GU_SLIST(GuTypeTableEntry, \
+			    __VA_ARGS__) \
+ }
+
+typedef struct GuTypeMap GuTypeMap;
+
+GuTypeMap*
+gu_new_type_map(GuTypeTable* table, GuPool* pool);
+
+void*
+gu_type_map_get(GuTypeMap* tmap, GuType* type);
+
+size_t 
+gu_type_size(GuType* type);
+
+GuTypeRepr*
+gu_type_repr(GuType* type);
+
+const void*
+gu_type_check_cast(GuType* t, GuKind* k);
+
+const void*
+gu_type_dyn_cast(GuType* t, GuKind* k);
+
+#define gu_type_try_cast(type_, k_) \
+	((GU_KIND_TYPE(k_)*)gu_type_dyn_cast(type_, gu_kind(k_)))
+
+#ifndef NDEBUG
+#define gu_type_cast(type_, k_) \
+	((GU_KIND_TYPE(k_)*)gu_type_check_cast(type_, gu_kind(k_)))
+#else
+#define gu_type_cast(type_, k_) \
+	((GU_KIND_TYPE(k_)*)(type_))
+#endif
+
+void* gu_type_malloc(GuType* type, GuPool* pool);
+
+#if 0
+void* gu_type_ptr_get(GuType* type, const void* pp);
+void gu_type_ptr_set(GuType* type, void* pp, void* p);
+#endif
+
+
+#endif // GU_TYPE_H_
diff --git a/src/runtime/c/gu/ucs.c b/src/runtime/c/gu/ucs.c
new file mode 100644
index 000000000..34649f36a
--- /dev/null
+++ b/src/runtime/c/gu/ucs.c
@@ -0,0 +1,135 @@
+#include <gu/ucs.h>
+#include <gu/assert.h>
+#include <guconfig.h>
+
+GU_DEFINE_TYPE(GuUCSExn, abstract, _);
+
+
+#ifdef GU_CHAR_ASCII
+
+bool
+gu_char_is_valid(char c)
+{
+	if (c < 0) {
+		return false;
+	} else if (c < 64) {
+		return UINT64_C(0xffffffef00003f81) & (UINT64_C(1) << c);
+	}
+#if CHAR_MAX > 127 // Let's avoid spurious warnings
+	else if (c > 127) {
+		return false;
+	}
+#endif	
+	return UINT64_C(0x7ffffffefffffffe) & (UINT64_C(1) << (c - 64));
+}
+
+char
+gu_ucs_char(GuUCS uc, GuExn* err)
+{
+	if (0 <= uc && uc <= 127) {
+		char c = (char) uc;
+		if (gu_char_is_valid(c)) {
+			return c;
+		}
+	}
+	gu_raise(err, GuUCSExn);
+	return 0;
+}
+
+#else // defined(GU_CHAR_ASCII)
+
+static const char gu_ucs_ascii[128] =
+	"\0\0\0\0\0\0\0\a\b\t\n\v\f\r\0\0"
+	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
+	" !\"#\0%&'()*+,-./0123456789:;<=>?"
+	"\0ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_"
+	"\0abcdefghijklmnopqrstuvwxyz{|}~\0";
+
+const uint8_t gu_ucs_ascii_reverse_[CHAR_MAX] = {
+	['\0'] = 0x00, ['\a'] = 0x07, ['\b'] = 0x08, ['\t'] = 0x09,
+	['\n'] = 0x0a, ['\v'] = 0x0b, ['\f'] = 0x0c, ['\r'] = 0x0d,
+	[' '] = 0x20, ['!'] = 0x21, ['"'] = 0x22, ['#'] = 0x23, ['%'] = 0x25,
+	['&'] = 0x26, ['\''] = 0x27, ['('] = 0x28, [')'] = 0x29, ['*'] = 0x2a,
+	['+'] = 0x2b, [','] = 0x2c, ['-'] = 0x2d, ['.'] = 0x2e, ['/'] = 0x2f,
+	['0'] = 0x30, ['1'] = 0x31, ['2'] = 0x32, ['3'] = 0x33, ['4'] = 0x34,
+	['5'] = 0x35, ['6'] = 0x36, ['7'] = 0x37, ['8'] = 0x38, ['9'] = 0x39,
+	[':'] = 0x3a, [';'] = 0x3b, ['<'] = 0x3c, ['='] = 0x3d, ['>'] = 0x3e,
+	['?'] = 0x3f, ['A'] = 0x41, ['B'] = 0x42, ['C'] = 0x43, ['D'] = 0x44,
+	['E'] = 0x45, ['F'] = 0x46, ['G'] = 0x47, ['H'] = 0x48, ['I'] = 0x49,
+	['J'] = 0x4a, ['K'] = 0x4b, ['L'] = 0x4c, ['M'] = 0x4d, ['N'] = 0x4e,
+	['O'] = 0x4f, ['P'] = 0x50, ['Q'] = 0x51, ['R'] = 0x52, ['S'] = 0x53,
+	['T'] = 0x54, ['U'] = 0x55, ['V'] = 0x56, ['W'] = 0x57, ['X'] = 0x58,
+	['Y'] = 0x59, ['Z'] = 0x5a, ['['] = 0x5b, ['\\'] = 0x5c, [']'] = 0x5d,
+	['^'] = 0x5e, ['_'] = 0x5f, ['a'] = 0x61, ['b'] = 0x62, ['c'] = 0x63,
+	['d'] = 0x64, ['e'] = 0x65, ['f'] = 0x66, ['g'] = 0x67, ['h'] = 0x68,
+	['i'] = 0x69, ['j'] = 0x6a, ['k'] = 0x6b, ['l'] = 0x6c, ['m'] = 0x6d,
+	['n'] = 0x6e, ['o'] = 0x6f, ['p'] = 0x70, ['q'] = 0x71, ['r'] = 0x72,
+	['s'] = 0x73, ['t'] = 0x74, ['u'] = 0x75, ['v'] = 0x76, ['w'] = 0x77,
+	['x'] = 0x78, ['y'] = 0x79, ['z'] = 0x7a, ['{'] = 0x7b, ['|'] = 0x7c,
+	['}'] = 0x7d, ['~'] = 0x7e
+};
+
+
+bool
+gu_char_is_valid(char c)
+{
+	if (c > 0) {
+		return (gu_ucs_ascii_reverse_[(int) c] > 0);
+	}
+	return (c == '\0');
+}
+
+char
+gu_ucs_char(GuUCS uc, GuExn* err)
+{
+	if (uc == 0) {
+		return '\0';
+	} else if (0 < uc && uc <= 127) {
+		char c = gu_ucs_ascii[uc];
+		if (c != '\0') {
+			return (unsigned char) c;
+		}
+	}
+	gu_raise(err, GuUCSExn);
+	return 0;
+}
+
+#endif
+
+size_t
+gu_str_to_ucs(const char* cbuf, size_t len, GuUCS* ubuf, GuExn* err)
+{
+	size_t n = 0;
+	while (n < len) {
+		char c = cbuf[n];
+		if (!gu_char_is_valid(c)) {
+			gu_raise(err, GuUCSExn);
+			return n;
+		}
+		ubuf[n] = gu_char_ucs(c);
+		n++;
+	}
+	return n;
+}
+
+size_t
+gu_ucs_to_str(const GuUCS* ubuf, size_t len, char* cbuf, GuExn* err)
+{
+	size_t n = 0;
+	while (n < len) {
+		char c = gu_ucs_char(ubuf[n], err);
+		if (!gu_ok(err)) {
+			break;
+		}
+		cbuf[n] = c;
+		n++;
+	}
+	return n;
+}
+
+
+extern inline bool
+gu_ucs_valid(GuUCS ucs);
+
+extern inline GuUCS
+gu_char_ucs(char c);
diff --git a/src/runtime/c/gu/ucs.h b/src/runtime/c/gu/ucs.h
new file mode 100644
index 000000000..f1662a602
--- /dev/null
+++ b/src/runtime/c/gu/ucs.h
@@ -0,0 +1,53 @@
+#ifndef GU_UCS_H_
+#define GU_UCS_H_
+
+#include <gu/defs.h>
+#include <gu/exn.h>
+#include <gu/assert.h>
+
+
+#if defined(__STDC_ISO_10646__) && WCHAR_MAX >= 0x10FFFF
+#include <wchar.h>
+#define GU_UCS_WCHAR
+typedef wchar_t GuUCS;
+#else
+typedef int32_t GuUCS;
+#endif
+
+#define GU_UCS_MAX ((GuUCS)(0x10FFFF))
+
+bool
+gu_char_is_valid(char c);
+
+inline bool
+gu_ucs_valid(GuUCS ucs)
+{
+	return ucs >= 0 && ucs <= GU_UCS_MAX;
+}
+
+inline GuUCS
+gu_char_ucs(char c)
+{
+	gu_require(gu_char_is_valid(c));
+#ifdef GU_CHAR_ASCII
+	GuUCS u = (GuUCS) c;
+#else
+	extern const uint8_t gu_ucs_ascii_reverse_[CHAR_MAX];
+	GuUCS u = gu_ucs_ascii_reverse_[(unsigned char) c];
+#endif
+	gu_ensure(u < 0x80);
+	return u;
+}
+
+char
+gu_ucs_char(GuUCS uc, GuExn* err);
+
+size_t
+gu_str_to_ucs(const char* cbuf, size_t len, GuUCS* ubuf, GuExn* err);
+
+size_t
+gu_ucs_to_str(const GuUCS* ubuf, size_t len, char* cbuf, GuExn* err);
+
+extern GU_DECLARE_TYPE(GuUCSExn, abstract);
+
+#endif // GU_ISO10646_H_
diff --git a/src/runtime/c/gu/utf8.c b/src/runtime/c/gu/utf8.c
new file mode 100644
index 000000000..a416c2dac
--- /dev/null
+++ b/src/runtime/c/gu/utf8.c
@@ -0,0 +1,220 @@
+#include <gu/assert.h>
+#include <gu/utf8.h>
+#include <guconfig.h>
+
+GuUCS
+gu_utf8_decode(const uint8_t** src_inout)
+{
+	const uint8_t* src = *src_inout;
+	uint8_t c = src[0];
+	if (c < 0x80) {
+		*src_inout = src + 1;
+		return (GuUCS) c;
+	}
+	size_t len = (c < 0xe0 ? 1 :
+		      c < 0xf0 ? 2 :
+		      3);
+	uint32_t mask = 0x07071f7f;
+	uint32_t u = c & (mask >> (len * 8));
+	for (size_t i = 1; i <= len; i++) {
+		c = src[i];
+		u = u << 6 | (c & 0x3f);
+	}
+	*src_inout = &src[len + 1];
+	return (GuUCS) u;
+}
+
+GuUCS
+gu_in_utf8_(GuIn* in, GuExn* err)
+{
+	uint8_t c = gu_in_u8(in, err);
+	if (!gu_ok(err)) {
+		return 0;
+	}
+	int len = (c < 0x80 ? 0 : 
+		   c < 0xc2 ? -1 :
+		   c < 0xe0 ? 1 :
+		   c < 0xf0 ? 2 :
+		   c < 0xf5 ? 3 :
+		   -1);
+	if (len < 0) {
+	 	goto fail;
+	} else if (len == 0) {
+		return c;
+	}
+	static const uint8_t mask[4] = { 0x7f, 0x1f, 0x0f, 0x07 };
+	uint32_t u = c & mask[len];
+	uint8_t buf[3];
+	// If reading the extra bytes causes EOF, it is an encoding
+	// error, not a legitimate end of character stream.
+	GuExn* tmp_err = gu_exn(err, GuEOF, NULL);
+	gu_in_bytes(in, buf, len, tmp_err);
+	if (tmp_err->caught) {
+		goto fail;
+	}
+	if (!gu_ok(err)) {
+		return 0;
+	}
+	for (int i = 0; i < len; i++) {
+		c = buf[i];
+		if ((c & 0xc0) != 0x80) {
+			goto fail;
+		}
+		u = u << 6 | (c & 0x3f);
+	}
+	GuUCS ucs = (GuUCS) u;
+	if (!gu_ucs_valid(ucs)) {
+		goto fail;
+	}
+	return ucs;
+
+fail:
+	gu_raise(err, GuUCSExn);
+	return 0;
+}
+
+
+size_t
+gu_advance_utf8(GuUCS ucs, uint8_t* buf)
+{
+	gu_require(gu_ucs_valid(ucs));
+	if (ucs < 0x80) {
+		buf[0] = (uint8_t) ucs;
+		return 1;
+	} else if (ucs < 0x800) {
+		buf[0] = 0xc0 | (ucs >> 6);
+		buf[1] = 0x80 | (ucs & 0x3f);
+		return 2;
+	} else if (ucs < 0x10000) {
+		buf[0] = 0xe0 | (ucs >> 12);
+		buf[1] = 0x80 | ((ucs >> 6) & 0x3f);
+		buf[2] = 0x80 | (ucs & 0x3f);
+		return 3;
+	} else {
+		buf[0] = 0xf0 | (ucs >> 18);
+		buf[1] = 0x80 | ((ucs >> 12) & 0x3f);
+		buf[2] = 0x80 | ((ucs >> 6) & 0x3f);
+		buf[3] = 0x80 | (ucs & 0x3f);
+		return 4;
+	}
+}
+
+char
+gu_in_utf8_char_(GuIn* in, GuExn* err)
+{
+	return gu_ucs_char(gu_in_utf8(in, err), err);
+}
+
+void
+gu_out_utf8_long_(GuUCS ucs, GuOut* out, GuExn* err)
+{
+	uint8_t buf[4];
+	size_t sz = gu_advance_utf8(ucs, buf);
+	switch (sz) {
+	case 2:
+		gu_out_bytes(out, buf, 2, err);
+		break;
+	case 3:
+		gu_out_bytes(out, buf, 3, err);
+		break;
+	case 4:
+		gu_out_bytes(out, buf, 4, err);
+		break;
+	default:
+		gu_impossible();
+	}
+}
+
+extern inline void
+gu_out_utf8(GuUCS ucs, GuOut* out, GuExn* err);
+
+static size_t 
+gu_utf32_out_utf8_buffered_(const GuUCS* src, size_t len, GuOut* out, 
+			    GuExn* err)
+{
+	size_t src_i = 0;
+	while (src_i < len) {
+		size_t dst_sz;
+		uint8_t* dst = gu_out_begin_span(out, len - src_i, &dst_sz, err);
+		if (!gu_ok(err)) {
+			return src_i;
+		}
+		if (!dst) {
+			gu_out_utf8(src[src_i], out, err);
+			if (!gu_ok(err)) {
+				return src_i;
+			}
+			src_i++;
+			break;
+		} 
+		size_t dst_i = 0;
+		while (true) {
+			size_t safe = (dst_sz - dst_i) / 4;
+			size_t end = GU_MIN(len, src_i + safe);
+			if (end == src_i) {
+				break;
+			}
+			do {
+				GuUCS ucs = src[src_i++];
+				dst_i += gu_advance_utf8(ucs, &dst[dst_i]);
+			} while (src_i < end);
+		} 
+		gu_out_end_span(out, dst_i);
+	}
+	return src_i;
+}
+
+size_t
+gu_utf32_out_utf8(const GuUCS* src, size_t len, GuOut* out, GuExn* err)
+{
+	if (gu_out_is_buffered(out)) {
+		return gu_utf32_out_utf8_buffered_(src, len, out, err);
+	} 
+	for (size_t i = 0; i < len; i++) {
+		gu_out_utf8(src[i], out, err);
+		if (!gu_ok(err)) {
+			return i;
+		}
+	}
+	return len;
+
+}
+
+#ifndef GU_CHAR_ASCII
+
+void gu_str_out_utf8_(const char* str, GuOut* out, GuExn* err)
+{
+	size_t len = strlen(str);
+	size_t sz = 0;
+	uint8_t* buf = gu_out_begin_span(out, len, &sz, err);
+	if (!gu_ok(err)) {
+		return;
+	}
+	if (buf != NULL && sz < len) {
+		gu_out_end_span(out, 0);
+		buf = NULL;
+	}
+	GuPool* tmp_pool = buf ? NULL : gu_local_pool();
+	buf = buf ? buf : gu_new_n(uint8_t, len, tmp_pool);
+	for (size_t i = 0; i < len; i++) {
+		GuUCS ucs = gu_char_ucs(str[i]);
+		buf[i] = (uint8_t) ucs;
+	}
+	if (tmp_pool) {
+		gu_out_bytes(out, buf, len, err);
+		gu_pool_free(tmp_pool);
+	} else {
+		gu_out_end_span(out, len);
+	}
+}
+
+#endif
+
+extern inline void 
+gu_str_out_utf8(const char* str, GuOut* out, GuExn* err);
+
+extern inline GuUCS
+gu_in_utf8(GuIn* in, GuExn* err);
+
+extern inline char
+gu_in_utf8_char(GuIn* in, GuExn* err);
diff --git a/src/runtime/c/gu/utf8.h b/src/runtime/c/gu/utf8.h
new file mode 100644
index 000000000..053d8664e
--- /dev/null
+++ b/src/runtime/c/gu/utf8.h
@@ -0,0 +1,67 @@
+#ifndef GU_UTF8_H_
+#define GU_UTF8_H_
+
+#include <gu/in.h>
+#include <gu/out.h>
+#include <gu/ucs.h>
+
+inline GuUCS
+gu_in_utf8(GuIn* in, GuExn* err)
+{
+	int i = gu_in_peek_u8(in);
+	if (i >= 0 && i < 0x80) {
+		gu_in_consume(in, 1);
+		return (GuUCS) i;
+	}
+	extern GuUCS gu_in_utf8_(GuIn* in, GuExn* err);
+	return gu_in_utf8_(in, err);
+}
+
+
+inline char
+gu_in_utf8_char(GuIn* in, GuExn* err)
+{
+#ifdef GU_CHAR_ASCII
+	int i = gu_in_peek_u8(in);
+	if (i >= 0 && i < 0x80) {
+		gu_in_consume(in, 1);
+		return (char) i;
+	}
+#endif
+	extern char gu_in_utf8_char_(GuIn* in, GuExn* err);
+	return gu_in_utf8_char_(in, err);
+}
+
+void
+gu_out_utf8_long_(GuUCS ucs, GuOut* out, GuExn* err);
+
+inline void
+gu_out_utf8(GuUCS ucs, GuOut* out, GuExn* err)
+{
+	gu_require(gu_ucs_valid(ucs));
+	if (GU_LIKELY(ucs < 0x80)) {
+		gu_out_u8(out, ucs, err);
+	} else {
+		gu_out_utf8_long_(ucs, out, err);
+	}
+}
+
+size_t
+gu_utf32_out_utf8(const GuUCS* src, size_t len, GuOut* out, GuExn* err);
+
+GuUCS
+gu_utf8_decode(const uint8_t** utf8);
+
+inline void 
+gu_str_out_utf8(const char* str, GuOut* out, GuExn* err)
+{
+#ifdef GU_CHAR_ASCII
+	gu_out_bytes(out, (const uint8_t*) str, strlen(str), err);
+#else
+	extern void 
+		gu_str_out_utf8_(const char* str, GuOut* out, GuExn* err);
+	gu_str_out_utf8_(str, out, err);
+#endif
+}
+
+#endif // GU_UTF8_H_
diff --git a/src/runtime/c/gu/variant.c b/src/runtime/c/gu/variant.c
new file mode 100644
index 000000000..62fdb92c1
--- /dev/null
+++ b/src/runtime/c/gu/variant.c
@@ -0,0 +1,100 @@
+/* 
+ * Copyright 2010 University of Helsinki.
+ *   
+ * This file is part of libgu.
+ * 
+ * Libgu is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ * 
+ * Libgu is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with libgu. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "variant.h"
+#include "bits.h"
+
+enum {
+	GU_VARIANT_ALIGNMENT = sizeof(uintptr_t)
+};
+
+void* 
+gu_alloc_variant(uint8_t tag, size_t size, 
+		 size_t align, GuVariant* variant_out, GuPool* pool)
+{
+	align = gu_max(align, GU_VARIANT_ALIGNMENT);
+	if (((size_t)tag) > GU_VARIANT_ALIGNMENT - 2) {
+		uint8_t* alloc = gu_malloc_aligned(pool, align + size, align);
+		alloc[align - 1] = tag;
+		void* p = &alloc[align];
+		variant_out->p = (uintptr_t)p;
+		return p;
+	}
+	void* p = gu_malloc_aligned(pool, size, align);
+	variant_out->p = ((uintptr_t)p) | (tag + 1);
+	return p;
+}
+
+GuVariant 
+gu_make_variant(uint8_t tag, size_t size, size_t align, const void* init,
+		GuPool* pool)
+{
+	GuVariant v;
+	void* data = gu_alloc_variant(tag, size, align, &v, pool);
+	memcpy(data, init, size);
+	return v;
+}
+
+int
+gu_variant_tag(GuVariant variant)
+{
+	if (gu_variant_is_null(variant)) {
+		return GU_VARIANT_NULL;
+	}
+	int u = variant.p % GU_VARIANT_ALIGNMENT;
+	if (u == 0) {
+		uint8_t* mem = (uint8_t*)variant.p;
+		return mem[-1];
+	}
+	return u - 1;
+}
+
+void*
+gu_variant_data(GuVariant variant)
+{
+	if (gu_variant_is_null(variant)) {
+		return NULL;
+	}
+	return (void*)gu_align_backward(variant.p, GU_VARIANT_ALIGNMENT);
+}
+
+GuVariantInfo gu_variant_open(GuVariant variant)
+{
+	GuVariantInfo info = {
+		.tag = gu_variant_tag(variant),
+		.data = gu_variant_data(variant)
+	};
+	return info;
+}
+
+int 
+gu_variant_intval(GuVariant variant)
+{
+	int u = variant.p % GU_VARIANT_ALIGNMENT;
+	if (u == 0) {
+		int* mem = (int*)variant.p;
+		return *mem;
+	}
+	return (variant.p / GU_VARIANT_ALIGNMENT);
+}
+
+const GuVariant gu_null_variant = { (GuWord) NULL };
+
+GU_DEFINE_KIND(GuVariant, repr);
+GU_DEFINE_KIND(GuVariantAsPtr, repr);
diff --git a/src/runtime/c/gu/variant.h b/src/runtime/c/gu/variant.h
new file mode 100644
index 000000000..a9bb10a4a
--- /dev/null
+++ b/src/runtime/c/gu/variant.h
@@ -0,0 +1,167 @@
+/* 
+ * Copyright 2010 University of Helsinki.
+ *   
+ * This file is part of libgu.
+ * 
+ * Libgu is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ * 
+ * Libgu is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with libgu. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file
+ *
+ * Lightweight tagged data.    
+ */
+
+#ifndef GU_VARIANT_H_
+#define GU_VARIANT_H_
+
+#include <gu/defs.h>
+#include <gu/mem.h>
+#include <gu/type.h>
+
+/** @name Variants
+ * @{
+ */
+
+typedef struct GuVariant GuVariant;
+
+
+void* gu_alloc_variant(uint8_t tag, 
+		       size_t size, size_t align, 
+		       GuVariant* variant_out, GuPool* pool);
+
+GuVariant gu_make_variant(uint8_t tag, 
+			  size_t size, size_t align, 
+			  const void* init, GuPool* pool);
+
+#define gu_new_variant(tag, type, variant_out, pool)	    \
+	((type*)gu_alloc_variant(tag, sizeof(type), \
+				 gu_alignof(type), variant_out, pool))
+
+/**< 
+ * @hideinitializer */
+
+#define gu_new_variant_i(POOL, TAG, T, ...)				\
+	gu_make_variant(TAG, sizeof(T), gu_alignof(T),			\
+			&(T){ __VA_ARGS__ }, POOL)
+
+
+
+#define gu_new_flex_variant(tag, type, flex_mem, n_elems, variant_out, pool)	\
+	((type*)gu_alloc_variant(tag,				\
+				 GU_FLEX_SIZE(type, flex_mem, n_elems), \
+				 gu_flex_alignof(type),			\
+				 variant_out, pool))
+/**< 
+ * @hideinitializer */
+
+enum {
+	GU_VARIANT_NULL = -1
+};
+
+int gu_variant_tag(GuVariant variant);
+
+void* gu_variant_data(GuVariant variant);
+
+
+typedef struct GuVariantInfo GuVariantInfo;
+
+struct GuVariantInfo {
+	int tag;
+	void* data;
+};
+
+GuVariantInfo gu_variant_open(GuVariant variant);
+
+/** @privatesection */
+struct GuVariant {
+	uintptr_t p;
+	/**< @private */
+};
+
+/** @} */
+
+static inline void*
+gu_variant_to_ptr(GuVariant variant)
+{
+	return (void*)variant.p;
+}
+
+static inline GuVariant
+gu_variant_from_ptr(const void* p)
+{
+	GuVariant v = { (uintptr_t)p };
+	return v;
+}
+
+extern const GuVariant gu_null_variant;
+
+static inline bool
+gu_variant_is_null(GuVariant v) {
+	return ((void*)v.p == NULL);
+}
+
+
+// variant
+
+typedef const struct GuConstructor GuConstructor;
+
+struct GuConstructor {
+	int c_tag;
+	const char* c_name;
+	const GuType* type;
+};
+
+#define GU_CONSTRUCTOR_V(ctag, c_type) {		\
+		.c_tag = ctag,	 \
+		.c_name = #ctag, \
+		.type = c_type \
+}
+
+#define GU_CONSTRUCTOR(ctag, t_) \
+	GU_CONSTRUCTOR_V(ctag, gu_type(t_))
+
+#define GU_CONSTRUCTOR_P(ctag, t_) \
+	GU_CONSTRUCTOR_V(ctag, gu_ptr_type(t_))
+
+#define GU_CONSTRUCTOR_S(ctag, t_, ...)		\
+	GU_CONSTRUCTOR_V(ctag, GU_TYPE_LIT(struct, t_, __VA_ARGS__))
+
+#define GU_CONSTRUCTOR_S1(ctag, t_, mem1_, type1_)			\
+	GU_CONSTRUCTOR_S(ctag, t_,					\
+			 GU_MEMBER(t_, mem1_, type1_))
+
+#define GU_CONSTRUCTOR_S2(ctag, t_, mem1_, type1_, mem2_, type2_)	\
+	GU_CONSTRUCTOR_S(ctag, t_,					\
+			 GU_MEMBER(t_, mem1_, type1_),			\
+			 GU_MEMBER(t_, mem2_, type2_))
+
+
+
+typedef GuSList(GuConstructor) GuConstructors;
+
+typedef const struct GuVariantType GuVariantType, GuType_GuVariant;
+
+struct GuVariantType {
+	GuType_repr repr_base;
+	GuConstructors ctors;
+};
+
+#define GU_TYPE_INIT_GuVariant(k_, t_, ...) {			\
+	.repr_base = GU_TYPE_INIT_repr(k_, GuVariant, _),	\
+	.ctors = GU_SLIST(GuConstructor, __VA_ARGS__) \
+}
+
+extern GU_DECLARE_KIND(GuVariant);
+
+#endif // GU_VARIANT_H_
diff --git a/src/runtime/c/gu/write.c b/src/runtime/c/gu/write.c
new file mode 100644
index 000000000..69573fb0d
--- /dev/null
+++ b/src/runtime/c/gu/write.c
@@ -0,0 +1,174 @@
+#include <gu/write.h>
+
+
+size_t
+gu_utf32_write(const GuUCS* src, size_t len, GuWriter* wtr, GuExn* err)
+{
+	return gu_utf32_out_utf8(src, len, &wtr->out_, err);
+}
+
+
+void
+gu_vprintf(const char* fmt, va_list args, GuWriter* wtr, GuExn* err)
+{
+	GuPool* tmp_pool = gu_local_pool();
+	char* str = gu_vasprintf(fmt, args, tmp_pool);
+	gu_puts(str, wtr, err);
+	gu_pool_free(tmp_pool);
+}
+
+void
+gu_printf(GuWriter* wtr, GuExn* err, const char* fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	gu_vprintf(fmt, args, wtr, err);
+	va_end(args);
+}
+
+
+GuWriter*
+gu_new_utf8_writer(GuOut* utf8_out, GuPool* pool)
+{
+	GuOutStream* stream = gu_out_proxy_stream(utf8_out, pool);
+	GuWriter* wtr = gu_new(GuWriter, pool);
+	wtr->out_ = gu_init_out(stream);
+	return wtr;
+}
+
+
+#if 0
+#ifdef GU_UCS_WCHAR
+#include <stdlib.h>
+#include <wchar.h>
+static const mbstate_t gu_init_mbstate; // implicitly initialized to zero
+#endif
+
+typedef struct GuLocaleWriter GuLocaleWriter;
+
+struct GuLocaleWriter {
+	GuOutWriter owtr;
+#ifdef GU_UCS_WCHAR
+	mbstate_t ps;
+	size_t mb_cur_max;
+#endif
+};
+
+size_t
+gu_locale_writer_write(GuWriter* wtr, const uint8_t* utf8_src, size_t sz, 
+		       GuExn* err)
+{
+	GuLocaleWriter* lwtr = (GuLocaleWriter*) wtr;
+	size_t done = 0;
+	static const size_t bufsize = 256;
+#ifdef GU_UCS_WCHAR
+	size_t margin = lwtr->mb_cur_max;
+#else
+	size_t margin = 1;
+#endif
+	GuOut* out = lwtr->owtr.out;
+	if (gu_out_is_buffered(out)) {
+		while (done < sz) {
+			size_t dst_sz;
+			uint8_t* dst = gu_out_begin_span(out, &dst_sz);
+			if (!dst) {
+				break;
+			}
+			if (dst_sz <= margin) {
+				gu_out_end_span(out, 0);
+				break;
+			}
+			size_t end = dst_sz - margin;
+			const uint8_t* 
+			size_t n = done;
+			while (n < sz && dst_i <= end) {
+#ifdef GU_UCS_WCHAR
+				GuUCS ucs = gu_
+				wchar_t wc = src[n];
+				size_t nb = wcrtomb((char*) p, wc, &lwtr->ps);
+#else
+			*p = (uint8_t) gu_ucs_char(buf[n], err);
+			size_t nb = 1;
+			if (!gu_ok(err)) {
+				gu_exn_clear(err);
+				nb = (size_t) -1;
+			}
+#endif
+			if (nb == (size_t) -1) {
+				*p++ = (uint8_t) '?';
+			} else {
+				p += nb;
+			}
+				
+			}
+			for (
+
+		}
+
+
+
+	}
+
+	uint8_t cbuf[256];
+	while (done < size && gu_ok(err)) {
+		uint8_t* p = cbuf;
+		uint8_t* edge = &cbuf[bufsize - margin];
+		size_t n;
+		for  (n = done; p <= edge && n < size; n++) {
+#ifdef GU_UCS_WCHAR
+			wchar_t wc = buf[n];
+			size_t nb = wcrtomb((char*) p, wc, &lwtr->ps);
+#else
+			*p = (uint8_t) gu_ucs_char(buf[n], err);
+			size_t nb = 1;
+			if (!gu_ok(err)) {
+				gu_exn_clear(err);
+				nb = (size_t) -1;
+			}
+#endif
+			if (nb == (size_t) -1) {
+				*p++ = (uint8_t) '?';
+			} else {
+				p += nb;
+			}
+		}
+		gu_out_bytes(lwtr->owtr.out, cbuf, p - cbuf, err);
+		if (gu_ok(err)) {
+			done = n;
+		}
+	}
+	return done;
+}
+
+GuWriter*
+gu_locale_writer(GuOut* out, GuPool* pool)
+{
+	GuLocaleWriter* lwtr = gu_new_s(
+		pool, GuLocaleWriter,
+		.wtr.out.output = gu_locale_writer_output,
+		.wtr.out.flush = gu_locale_writer_flush,
+		.out = out);
+#ifdef GU_UCS_WCHAR
+	lwtr->ps = gu_init_mbstate;
+	lwtr->mb_cur_max = MB_CUR_MAX;
+#endif
+	return (GuWriter*) lwtr;
+}
+
+#endif
+
+extern inline void
+gu_ucs_write(GuUCS ucs, GuWriter* wtr, GuExn* err);
+
+extern inline void
+gu_writer_flush(GuWriter* wtr, GuExn* err);
+
+extern inline void
+gu_putc(char c, GuWriter* wtr, GuExn* err);
+
+extern inline void
+gu_puts(const char* str, GuWriter* wtr, GuExn* err);
+
+extern inline size_t
+gu_utf8_write(const uint8_t* src, size_t sz, GuWriter* wtr, GuExn* err);
+
diff --git a/src/runtime/c/gu/write.h b/src/runtime/c/gu/write.h
new file mode 100644
index 000000000..414a7bc2c
--- /dev/null
+++ b/src/runtime/c/gu/write.h
@@ -0,0 +1,64 @@
+#ifndef GU_WRITE_H_
+#define GU_WRITE_H_
+
+#include <gu/exn.h>
+#include <gu/ucs.h>
+#include <gu/out.h>
+#include <gu/utf8.h>
+
+typedef struct GuWriter GuWriter;
+
+struct GuWriter {
+	GuOut out_;
+};
+
+size_t
+gu_utf32_write(const GuUCS* buf, size_t size, GuWriter* wtr, GuExn* err);
+
+inline void
+gu_writer_flush(GuWriter* wtr, GuExn* err)
+{
+	gu_out_flush(&wtr->out_, err);
+}
+
+inline void
+gu_ucs_write(GuUCS ucs, GuWriter* wtr, GuExn* err)
+{
+	gu_out_utf8(ucs, &wtr->out_, err);
+}
+
+inline void
+gu_putc(char c, GuWriter* wtr, GuExn* err)
+{
+	GuUCS ucs = gu_char_ucs(c);
+	gu_out_u8(&wtr->out_, (uint8_t) ucs, err);
+}
+
+inline void
+gu_puts(const char* str, GuWriter* wtr, GuExn* err)
+{
+	gu_str_out_utf8(str, &wtr->out_, err);
+}
+
+inline size_t
+gu_utf8_write(const uint8_t* src, size_t sz, GuWriter* wtr, GuExn* err)
+{
+	return gu_out_bytes(&wtr->out_, src, sz, err);
+}
+
+void
+gu_vprintf(const char* fmt, va_list args, GuWriter* wtr, GuExn* err);
+
+void
+gu_printf(GuWriter* wtr, GuExn* err, const char* fmt, ...);
+
+//GuWriter
+//gu_init_utf8_writer(GuOut* utf8_out);
+
+GuWriter*
+gu_new_utf8_writer(GuOut* utf8_out, GuPool* pool);
+
+GuWriter*
+gu_make_locale_writer(GuOut* locale_out, GuPool* pool);
+
+#endif // GU_WRITE_H_
diff --git a/src/runtime/c/gu/yaml.c b/src/runtime/c/gu/yaml.c
new file mode 100644
index 000000000..4d769a4aa
--- /dev/null
+++ b/src/runtime/c/gu/yaml.c
@@ -0,0 +1,339 @@
+#include <gu/yaml.h>
+#include <gu/seq.h>
+#include <gu/assert.h>
+#include <gu/read.h>
+#include <gu/ucs.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <ctype.h>
+
+
+const GuYamlAnchor gu_yaml_null_anchor = 0;
+
+typedef const struct GuYamlState GuYamlState;
+
+struct GuYamlState {
+	const char* prefix;
+	const char* suffix;
+	GuYamlState* next;
+};
+
+static const struct {
+	GuYamlState document, first_key, key, value, first_elem, elem;
+} gu_yaml_states = {
+	.document = {
+		.prefix = "---\n",
+		.suffix = "\n...\n",
+		.next = &gu_yaml_states.document,
+	},
+	.key = {
+		.prefix = "? ",
+		.next = &gu_yaml_states.value,
+	},
+	.value = {
+		.prefix = ": ",
+		.suffix = ",",
+		.next = &gu_yaml_states.key,
+	},
+	.elem = {
+		.suffix = ",",
+		.next = &gu_yaml_states.elem,
+	},
+};
+
+typedef const struct GuYamlFrameClass GuYamlFrameClass;
+
+struct GuYamlFrameClass {
+	const char* open;
+	GuYamlState* first;
+	const char* close;
+};
+
+static const struct {
+	GuYamlFrameClass document, mapping, sequence;
+} gu_yaml_frame_classes = {
+	.mapping = {
+		.open = "{",
+		.first = &gu_yaml_states.key,
+		.close = "}",
+	},
+	.sequence = {
+		.open = "[",
+		.first = &gu_yaml_states.elem,
+		.close = "]",
+	},
+};
+
+typedef struct GuYamlFrame GuYamlFrame;
+
+struct GuYamlFrame {
+	GuYamlFrameClass* klass;
+	GuYamlState* next;
+};
+
+typedef GuBuf GuYamlStack;
+
+struct GuYaml {
+	GuWriter* wtr;
+	GuExn* err;
+	GuPool* pool;
+	GuYamlState* state;
+	bool in_node;
+	bool have_anchor;
+	bool have_tag; 
+	int next_anchor;
+	bool indent;
+	int indent_level;
+	bool indented;
+	GuYamlStack* stack;
+};
+
+
+GuYaml*
+gu_new_yaml(GuWriter* wtr, GuExn* err, GuPool* pool)
+{
+	GuYaml* yaml = gu_new(GuYaml, pool);
+	yaml->wtr = wtr;
+	yaml->pool = pool;
+	yaml->err = err;
+	yaml->state = &gu_yaml_states.document;
+	yaml->in_node = false;
+	yaml->have_anchor = false;
+	yaml->have_tag = false;
+	yaml->next_anchor = 1;
+	yaml->stack = gu_new_buf(GuYamlFrame, pool);
+	yaml->indent = true;
+	yaml->indent_level = 0;
+	yaml->indented = false;
+	return yaml;
+}
+
+static void
+gu_yaml_printf(GuYaml* yaml, const char* fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	gu_vprintf(fmt, args, yaml->wtr, yaml->err);
+	va_end(args);
+}
+
+static void
+gu_yaml_putc(GuYaml* yaml, char c)
+{
+	gu_putc(c, yaml->wtr, yaml->err);
+}
+
+static void
+gu_yaml_puts(GuYaml* yaml, const char* str)
+{
+	gu_puts(str, yaml->wtr, yaml->err);
+}
+
+static void
+gu_yaml_begin_line(GuYaml* yaml)
+{
+	if (yaml->indent && !yaml->indented) {
+		for (int i = 0; i < yaml->indent_level; i++) {
+			gu_yaml_putc(yaml, ' ');
+		}
+		yaml->indented = true;
+	}
+}
+
+static void
+gu_yaml_end_line(GuYaml* yaml)
+{
+	if (yaml->indent) {
+		gu_yaml_putc(yaml, '\n');
+	}
+	yaml->indented = false;
+}
+
+
+static void 
+gu_yaml_begin_node(GuYaml* yaml)
+{
+	gu_yaml_begin_line(yaml);
+	if (!yaml->in_node) {
+		if (yaml->state->prefix != NULL) {
+			gu_yaml_puts(yaml, yaml->state->prefix);
+		}
+		yaml->in_node = true;
+	}
+}
+
+static void
+gu_yaml_end_node(GuYaml* yaml)
+{
+	gu_assert(yaml->in_node);
+	if (yaml->state->suffix != NULL) {
+		gu_yaml_puts(yaml, yaml->state->suffix);
+	}
+	gu_yaml_end_line(yaml);
+	yaml->in_node = false;
+	yaml->have_anchor = false;
+	yaml->have_tag = false;
+	if (yaml->state != NULL) {
+		yaml->state = yaml->state->next;
+	}
+}
+
+static void
+gu_yaml_begin(GuYaml* yaml, GuYamlFrameClass* klass)
+{
+	gu_yaml_begin_node(yaml);
+	gu_yaml_puts(yaml, klass->open);
+	gu_buf_push(yaml->stack, GuYamlFrame,
+		    ((GuYamlFrame) { .klass = klass, .next = yaml->state}));
+	yaml->state = klass->first;
+	yaml->in_node = yaml->have_anchor = yaml->have_tag = false;
+	gu_yaml_end_line(yaml);
+	yaml->indent_level++;
+}
+
+void
+gu_yaml_begin_mapping(GuYaml* yaml)
+{
+	gu_yaml_begin(yaml, &gu_yaml_frame_classes.mapping);
+}
+
+void
+gu_yaml_begin_sequence(GuYaml* yaml)
+{
+	gu_yaml_begin(yaml, &gu_yaml_frame_classes.sequence);
+}
+
+void 
+gu_yaml_end(GuYaml* yaml)
+{
+	gu_assert(!yaml->in_node);
+	yaml->indent_level--;
+	gu_yaml_begin_line(yaml);
+	GuYamlFrame f = gu_buf_pop(yaml->stack, GuYamlFrame);
+	gu_yaml_puts(yaml, f.klass->close);
+	yaml->state = f.next;
+	yaml->in_node = true;
+	gu_yaml_end_node(yaml);
+}
+
+
+void 
+gu_yaml_scalar(GuYaml* yaml, GuString s)
+{
+	gu_yaml_begin_node(yaml);
+	gu_yaml_putc(yaml, '"');
+	GuPool* tmp_pool = gu_local_pool();
+	GuReader* rdr = gu_string_reader(s, tmp_pool);
+	GuExn* err = gu_exn(yaml->err, GuEOF, NULL);
+	
+	static const char esc[0x20] = {
+		[0x00] = '0',
+		[0x07] = 'a', 'b', 't', 'n', 'v', 'f', 'r',
+		[0x1b] = 'e'
+	};
+
+	while (true) {
+		GuUCS u = gu_read_ucs(rdr, err);
+		if (!gu_ok(err)) {
+			break;
+		}
+		if (GU_LIKELY(u >= 0x20 && u < 0x7f)) {
+			if (GU_UNLIKELY(u == 0x22 || u == 0x5c)) {
+				gu_yaml_putc(yaml, '\\');
+			}
+			gu_ucs_write(u, yaml->wtr, yaml->err);
+		} else if (GU_UNLIKELY(u < 0x20 && esc[u])) {
+			gu_yaml_printf(yaml, "\\%c", esc[u]);
+		} else if (GU_UNLIKELY(u <= 0x9f)) {
+			gu_yaml_printf(yaml, "\\x%02x", (unsigned) u);
+		} else if (GU_UNLIKELY((u >= 0xd800 && u <= 0xdfff) ||
+				       (u >= 0xfffe && u <= 0xffff))) {
+			gu_yaml_printf(yaml, "\\u%04x", (unsigned) u);
+		} else {
+			gu_ucs_write(u, yaml->wtr, yaml->err);
+		}
+	}
+	gu_pool_free(tmp_pool);
+	gu_yaml_putc(yaml, '"');
+	gu_yaml_end_node(yaml);
+}
+
+static void 
+gu_yaml_tag(GuYaml* yaml, const char* format, ...)
+{
+	gu_yaml_begin_node(yaml);
+	gu_assert(!yaml->have_tag);
+	gu_yaml_putc(yaml, '!');
+	va_list args;
+	va_start(args, format);
+	gu_vprintf(format, args, yaml->wtr, yaml->err);
+	va_end(args);
+	gu_yaml_putc(yaml, ' ');
+	yaml->have_tag = true;
+}
+
+void 
+gu_yaml_tag_primary(GuYaml* yaml, const char* tag) 
+{
+	// TODO: check tag validity
+	gu_yaml_tag(yaml, "%s", tag);
+}
+
+void
+gu_yaml_tag_secondary(GuYaml* yaml, const char* tag)
+{
+	// TODO: check tag validity
+	gu_yaml_tag(yaml, "!%s", tag);
+}
+
+void
+gu_yaml_tag_named(GuYaml* yaml, const char* handle, const char* tag)
+{
+	// TODO: check tag validity
+	gu_yaml_tag(yaml, "%s!%s", handle, tag);
+}
+
+void
+gu_yaml_tag_verbatim(GuYaml* yaml, const char* uri)
+{
+	// XXX: uri escaping?
+	gu_yaml_tag(yaml, "<%s>", uri);
+}
+
+void
+gu_yaml_tag_non_specific(GuYaml* yaml)
+{
+	gu_yaml_tag(yaml, "");
+}
+
+GuYamlAnchor
+gu_yaml_anchor(GuYaml* yaml)
+{
+	gu_yaml_begin_node(yaml);
+	gu_assert(!yaml->have_anchor);
+	yaml->have_anchor = true;
+	int anchor = yaml->next_anchor++;
+	gu_yaml_printf(yaml, "&%d ", anchor);
+	return anchor;
+}
+
+void
+gu_yaml_alias(GuYaml* yaml, GuYamlAnchor anchor)
+{
+	gu_yaml_begin_node(yaml);
+	gu_assert(!yaml->have_anchor && !yaml->have_tag);
+	gu_yaml_printf(yaml, "*%d ", anchor);
+	gu_yaml_end_node(yaml);
+	return;
+}
+
+void gu_yaml_comment(GuYaml* yaml, GuString s)
+{
+	gu_yaml_begin_line(yaml);
+	gu_yaml_puts(yaml, "# ");
+	// TODO: verify no newlines in comment
+	gu_string_write(s, yaml->wtr, yaml->err);
+	gu_yaml_puts(yaml, "\n");
+	yaml->indented = false;
+}
+
diff --git a/src/runtime/c/gu/yaml.h b/src/runtime/c/gu/yaml.h
new file mode 100644
index 000000000..5a61d0786
--- /dev/null
+++ b/src/runtime/c/gu/yaml.h
@@ -0,0 +1,38 @@
+#ifndef GU_YAML_H_
+#define GU_YAML_H_
+
+#include <gu/mem.h>
+#include <gu/write.h>
+#include <gu/string.h>
+
+typedef struct GuYaml GuYaml;
+
+typedef int GuYamlAnchor;
+
+extern const GuYamlAnchor gu_yaml_null_anchor;
+
+GuYaml* gu_new_yaml(GuWriter* wtr, GuExn* err, GuPool* pool);
+
+GuYamlAnchor gu_yaml_anchor(GuYaml* yaml);
+
+void gu_yaml_tag_primary(GuYaml* yaml, const char* tag);
+void gu_yaml_tag_secondary(GuYaml* yaml, const char* tag);
+void gu_yaml_tag_named(GuYaml* yaml, const char* handle, const char* tag);
+void gu_yaml_tag_verbatim(GuYaml* yaml, const char* uri);
+void gu_yaml_tag_non_specific(GuYaml* yaml);
+void gu_yaml_comment(GuYaml* yaml, GuString comment);
+
+
+void gu_yaml_scalar(GuYaml* yaml, GuString scalar);
+
+void gu_yaml_alias(GuYaml* yaml, GuYamlAnchor anchor);
+
+void gu_yaml_begin_document(GuYaml* yaml);
+
+void gu_yaml_begin_sequence(GuYaml* yaml);
+
+void gu_yaml_begin_mapping(GuYaml* yaml);
+
+void gu_yaml_end(GuYaml* yaml);
+
+#endif // GU_YAML_H_