From 2905d5552c1530185609fe892e0e9e2c4994ca1d Mon Sep 17 00:00:00 2001 From: aarne Date: Fri, 5 Oct 2007 13:38:10 +0000 Subject: removed Canon/GFCC --- src/GF/GFCC/doc/gfcc.html | 842 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 842 insertions(+) create mode 100644 src/GF/GFCC/doc/gfcc.html (limited to 'src/GF/GFCC/doc/gfcc.html') diff --git a/src/GF/GFCC/doc/gfcc.html b/src/GF/GFCC/doc/gfcc.html new file mode 100644 index 000000000..c43188e9f --- /dev/null +++ b/src/GF/GFCC/doc/gfcc.html @@ -0,0 +1,842 @@ + + + + +The GFCC Grammar Format + +

The GFCC Grammar Format

+ +Aarne Ranta
+October 19, 2006 +
+ +

+
+

+ + +

+
+

+

+Author's address: +http://www.cs.chalmers.se/~aarne +

+

+History: +

+ + + +

What is GFCC

+

+GFCC is a low-level format for GF grammars. Its aim is to contain the minimum +that is needed to process GF grammars at runtime. This minimality has three +advantages: +

+ + +

+The idea is that all embedded GF applications are compiled to GFCC. +The GF system would be primarily used as a compiler and as a grammar +development tool. +

+

+Since GFCC is implemented in BNFC, a parser of the format is readily +available for C, C++, Haskell, Java, and OCaml. Also an XML +representation is generated in BNFC. A +reference implementation +of linearization and some other functions has been written in Haskell. +

+ +

GFCC vs. GFC

+

+GFCC is aimed to replace GFC as the run-time grammar format. GFC was designed +to be a run-time format, but also to +support separate compilation of grammars, i.e. +to store the results of compiling +individual GF modules. But this means that GFC has to contain extra information, +such as type annotations, which is only needed in compilation and not at +run-time. In particular, the pattern matching syntax and semantics of GFC is +complex and therefore difficult to implement in new platforms. +

+

+The main differences of GFCC compared with GFC can be summarized as follows: +

+ + +

+Here is an example of a GF grammar, consisting of three modules, +as translated to GFCC. The representations are aligned, with the exceptions +due to the alphabetical sorting of GFCC grammars. +

+
+                                      grammar Ex(Eng,Swe);
+  
+  abstract Ex = {                     abstract {
+    cat 
+      S ; NP ; VP ;
+    fun 
+      Pred : NP -> VP -> S ;            Pred : NP,VP -> S = (Pred);
+      She, They : NP ;                  She : -> NP = (She);
+      Sleep : VP ;                      Sleep : -> VP = (Sleep); 
+                                        They : -> NP = (They);
+  }                                     } ;
+                                      
+  concrete Eng of Ex = {              concrete Eng {
+    lincat
+      S  = {s : Str} ;
+      NP = {s : Str ; n : Num} ;
+      VP = {s : Num => Str} ;
+    param
+      Num = Sg | Pl ;
+    lin
+      Pred np vp = {                    Pred = [(($0!1),(($1!0)!($0!0)))];
+        s = np.s ++ vp.s ! np.n} ;      
+      She = {s = "she" ; n = Sg} ;      She = [0, "she"];
+      They = {s = "they" ; n = Pl} ;    
+      Sleep = {s = table {              Sleep = [("sleep" + ["s",""])];
+        Sg => "sleeps" ; 
+        Pl => "sleep"                   They = [1, "they"];
+        }                               } ;
+      } ;
+  }
+  
+  concrete Swe of Ex = {              concrete Swe {
+    lincat
+      S  = {s : Str} ;
+      NP = {s : Str} ;
+      VP = {s : Str} ;
+    param
+      Num = Sg | Pl ;
+    lin
+      Pred np vp = {                    Pred = [(($0!0),($1!0))];
+        s = np.s ++ vp.s} ;
+      She = {s = "hon"} ;               She = ["hon"];
+      They = {s = "de"} ;               They = ["de"];
+      Sleep = {s = "sover"} ;           Sleep = ["sover"];
+  }                                     } ;                                   
+
+

+ +

The syntax of GFCC files

+ +

Top level

+

+A grammar has a header telling the name of the abstract syntax +(often specifying an application domain), and the names of +the concrete languages. The abstract syntax and the concrete +syntaxes themselves follow. +

+
+    Grammar  ::= Header ";" Abstract ";" [Concrete] ;
+    Header   ::= "grammar" CId "(" [CId] ")" ;
+    Abstract ::= "abstract" "{" [AbsDef] "}" ;
+    Concrete ::= "concrete" CId "{" [CncDef] "}" ;
+
+

+Abstract syntax judgements give typings and semantic definitions. +Concrete syntax judgements give linearizations. +

+
+    AbsDef   ::= CId ":" Type "=" Exp ;
+    CncDef   ::= CId "=" Term ;
+
+

+Also flags are possible, local to each "module" (i.e. abstract and concretes). +

+
+    AbsDef   ::= "%" CId "=" String ;
+    CncDef   ::= "%" CId "=" String ;
+
+

+For the run-time system, the reference implementation in Haskell +uses a structure that gives efficient look-up: +

+
+    data GFCC = GFCC {
+      absname   :: CId ,
+      cncnames  :: [CId] ,
+      abstract  :: Abstr ,
+      concretes :: Map CId Concr
+      }
+  
+    data Abstr = Abstr {
+      funs :: Map CId Type,   -- find the type of a fun
+      cats :: Map CId [CId]   -- find the funs giving a cat
+      }
+  
+    type Concr = Map CId Term
+
+

+ +

Abstract syntax

+

+Types are first-order function types built from +category symbols. Syntax trees (Exp) are +rose trees with the head (Atom) either a function +constant, a metavariable, or a string, integer, or float +literal. +

+
+    Type     ::= [CId] "->" CId ;
+    Exp      ::= "(" Atom [Exp] ")" ;
+    Atom     ::= CId ;        -- function constant
+    Atom     ::= "?" ;        -- metavariable
+    Atom     ::= String ;     -- string literal
+    Atom     ::= Integer ;    -- integer literal
+    Atom     ::= Double ;     -- float literal
+
+

+ +

Concrete syntax

+

+Linearization terms (Term) are built as follows. +Constructor names are shown to make the later code +examples readable. +

+
+    R.  Term ::= "[" [Term] "]" ;        -- array
+    P.  Term ::= "(" Term "!" Term ")" ; -- access to indexed field
+    S.  Term ::= "(" [Term] ")" ;        -- sequence with ++
+    K.  Term ::= Tokn ;                  -- token
+    V.  Term ::= "$" Integer ;           -- argument
+    C.  Term ::= Integer ;               -- array index
+    FV. Term ::= "[|" [Term] "|]" ;      -- free variation
+    TM. Term ::= "?" ;                   -- linearization of metavariable
+
+

+Tokens are strings or (maybe obsolescent) prefix-dependent +variant lists. +

+
+    KS.  Tokn     ::= String ;
+    KP.  Tokn     ::= "[" "pre" [String] "[" [Variant] "]" "]" ;
+    Var. Variant  ::= [String] "/" [String] ;
+
+

+Three special forms of terms are introduced by the compiler +as optimizations. They can in principle be eliminated, but +their presence makes grammars much more compact. Their semantics +will be explained in a later section. +

+
+    F.  Term ::= CId ;                     -- global constant
+    W.  Term ::= "(" String "+" Term ")" ; -- prefix + suffix table
+    RP. Term ::= "(" Term "@" Term ")";    -- record parameter alias
+
+

+Identifiers are like Ident in GF and GFC, except that +the compiler produces constants prefixed with _ in +the common subterm elimination optimization. +

+
+    token CId (('_' | letter) (letter | digit | '\'' | '_')*) ;
+
+

+ +

The semantics of concrete syntax terms

+ +

Linearization and realization

+

+The linearization algorithm is essentially the same as in +GFC: a tree is linearized by evaluating its linearization term +in the environment of the linearizations of the subtrees. +Literal atoms are linearized in the obvious way. +The function also needs to know the language (i.e. concrete syntax) +in which linearization is performed. +

+
+    linExp :: GFCC -> CId -> Exp -> Term
+    linExp mcfg lang tree@(Tr at trees) = case at of
+      AC fun -> comp (Prelude.map lin trees) $ look fun
+      AS s   -> R [kks (show s)] -- quoted
+      AI i   -> R [kks (show i)]
+      AF d   -> R [kks (show d)]
+      AM     -> TM
+     where
+       lin  = linExp mcfg lang
+       comp = compute mcfg lang
+       look = lookLin mcfg lang
+
+

+The result of linearization is usually a record, which is realized as +a string using the following algorithm. +

+
+    realize :: Term -> String
+    realize trm = case trm of
+      R (t:_)  -> realize t
+      S ss     -> unwords $ Prelude.map realize ss
+      K (KS s) -> s
+      K (KP s _) -> unwords s ---- prefix choice TODO
+      W s t    -> s ++ realize t
+      FV (t:_) -> realize t
+      TM       -> "?"
+
+

+Since the order of record fields is not necessarily +the same as in GF source, +this realization does not work securely for +categories whose lincats more than one field. +

+ +

Term evaluation

+

+Evaluation follows call-by-value order, with two environments +needed: +

+ + +

+The code is presented in one-level pattern matching, to +enable reimplementations in languages that do not permit +deep patterns (such as Java and C++). +

+
+  compute :: GFCC -> CId -> [Term] -> Term -> Term
+  compute mcfg lang args = comp where
+    comp trm = case trm of
+      P r p  -> proj (comp r) (comp p)
+      RP i t -> RP (comp i) (comp t)
+      W s t  -> W s (comp t)
+      R ts   -> R $ Prelude.map comp ts
+      V i    -> idx args (fromInteger i)  -- already computed
+      F c    -> comp $ look c             -- not computed (if contains V)
+      FV ts  -> FV $ Prelude.map comp ts
+      S ts   -> S $ Prelude.filter (/= S []) $ Prelude.map comp ts
+      _ -> trm
+  
+    look = lookLin mcfg lang
+  
+    idx xs i = xs !! i
+  
+    proj r p = case (r,p) of
+      (_,     FV ts) -> FV $ Prelude.map (proj r) ts
+      (W s t, _)     -> kks (s ++ getString (proj t p))
+      _              -> comp $ getField r (getIndex p)
+  
+    getString t = case t of
+      K (KS s) -> s
+      _ -> trace ("ERROR in grammar compiler: string from "++ show t) "ERR"
+  
+    getIndex t =  case t of
+      C i    -> fromInteger i
+      RP p _ -> getIndex p
+      TM     -> 0  -- default value for parameter
+      _ -> trace ("ERROR in grammar compiler: index from " ++ show t) 0
+  
+    getField t i = case t of
+      R rs   -> idx rs i
+      RP _ r -> getField r i
+      TM     -> TM
+      _ -> trace ("ERROR in grammar compiler: field from " ++ show t) t
+
+

+ +

The special term constructors

+

+The three forms introduced by the compiler may a need special +explanation. +

+

+Global constants +

+
+    Term ::= CId ;
+
+

+are shorthands for complex terms. They are produced by the +compiler by (iterated) common subexpression elimination. +They are often more powerful than hand-devised code sharing in the source +code. They could be computed off-line by replacing each identifier by +its definition. +

+

+Prefix-suffix tables +

+
+    Term ::= "(" String "+" Term ")" ; 
+
+

+represent tables of word forms divided to the longest common prefix +and its array of suffixes. In the example grammar above, we have +

+
+    Sleep = [("sleep" + ["s",""])]
+
+

+which in fact is equal to the array of full forms +

+
+    ["sleeps", "sleep"]
+
+

+The power of this construction comes from the fact that suffix sets +tend to be repeated in a language, and can therefore be collected +by common subexpression elimination. It is this technique that +explains the used syntax rather than the more accurate +

+
+    "(" String "+" [String] ")"
+
+

+since we want the suffix part to be a Term for the optimization to +take effect. +

+

+The most curious construct of GFCC is the parameter array alias, +

+
+    Term ::= "(" Term "@" Term ")";
+
+

+This form is used as the value of parameter records, such as the type +

+
+    {n : Number ; p : Person}
+
+

+The problem with parameter records is their double role. +They can be used like parameter values, as indices in selection, +

+
+    VP.s ! {n = Sg ; p = P3}
+
+

+but also as records, from which parameters can be projected: +

+
+    {n = Sg ; p = P3}.n
+
+

+Whichever use is selected as primary, a prohibitively complex +case expression must be generated at compilation to GFCC to get the +other use. The adopted +solution is to generate a pair containing both a parameter value index +and an array of indices of record fields. For instance, if we have +

+
+    param Number = Sg | Pl ; Person = P1 | P2 | P3 ;
+
+

+we get the encoding +

+
+    {n = Sg ; p = P3}  ---> (2 @ [0,2])
+
+

+The GFCC computation rules are essentially +

+
+    (t ! (i @ _)) = (t ! i)
+    ((_ @ r) ! j)  =(r ! j)
+
+

+ +

Compiling to GFCC

+

+Compilation to GFCC is performed by the GF grammar compiler, and +GFCC interpreters need not know what it does. For grammar writers, +however, it might be interesting to know what happens to the grammars +in the process. +

+

+The compilation phases are the following +

+
    +
  1. translate GF source to GFC, as always in GF +
  2. undo GFC back-end optimizations +
  3. perform the values optimization to normalize tables +
  4. create a symbol table mapping the GFC parameter and record types to + fixed-size arrays, and parameter values and record labels to integers +
  5. traverse the linearization rules replacing parameters and labels by integers +
  6. reorganize the created GFC grammar so that it has just one abstract syntax + and one concrete syntax per language +
  7. apply UTF8 encoding to the grammar, if not yet applied (this is told by the + coding flag) +
  8. translate the GFC syntax tree to a GFCC syntax tree, using a simple + compositional mapping +
  9. perform the word-suffix optimization on GFCC linearization terms +
  10. perform subexpression elimination on each concrete syntax module +
  11. print out the GFCC code +
+ +

+Notice that a major part of the compilation is done within GFC, so that +GFC-related tasks (such as parser generation) could be performed by +using the old algorithms. +

+ +

Problems in GFCC compilation

+

+Two major problems had to be solved in compiling GFC to GFCC: +

+ + +

+The current implementation is still experimental and may fail +to generate correct code. Any errors remaining are likely to be +related to the two problems just mentioned. +

+

+The order problem is solved in different ways for tables and records. +For tables, the values optimization of GFC already manages to +maintain a canonical order. But this order can be destroyed by the +share optimization. To make sure that GFCC compilation works properly, +it is safest to recompile the GF grammar by using the values +optimization flag. +

+

+Records can be canonically ordered by sorting them by labels. +In fact, this was done in connection of the GFCC work as a part +of the GFC generation, to guarantee consistency. This means that +e.g. the s field will in general no longer appear as the first +field, even if it does so in the GF source code. But relying on the +order of fields in a labelled record would be misplaced anyway. +

+

+The canonical form of records is further complicated by lock fields, +i.e. dummy fields of form lock_C = <>, which are added to grammar +libraries to force intensionality of linearization types. The problem +is that the absence of a lock field only generates a warning, not +an error. Therefore a GFC grammar can contain objects of the same +type with and without a lock field. This problem was solved in GFCC +generation by just removing all lock fields (defined as fields whose +type is the empty record type). This has the further advantage of +(slightly) reducing the grammar size. More importantly, it is safe +to remove lock fields, because they are never used in computation, +and because intensional types are only needed in grammars reused +as libraries, not in grammars used at runtime. +

+

+While the order problem is rather bureaucratic in nature, run-time +variables are an interesting problem. They arise in the presence +of complex parameter values, created by argument-taking constructors +and parameter records. To give an example, consider the GF parameter +type system +

+
+    Number = Sg | Pl ;
+    Person = P1 | P2 | P3 ;
+    Agr = Ag Number Person ;
+
+

+The values can be translated to integers in the expected way, +

+
+    Sg = 0, Pl = 1
+    P1 = 0, P2 = 1, P3 = 2
+    Ag Sg P1 = 0, Ag Sg P2 = 1, Ag Sg P3 = 2,
+    Ag Pl P1 = 3, Ag Pl P2 = 4, Ag Pl P3 = 5
+
+

+However, an argument of Agr can be a run-time variable, as in +

+
+    Ag np.n P3
+
+

+This expression must first be translated to a case expression, +

+
+    case np.n of {
+      0 => 2 ;
+      1 => 5
+      }
+
+

+which can then be translated to the GFCC term +

+
+    ([2,5] ! ($0 ! $1))  
+
+

+assuming that the variable np is the first argument and that its +Number field is the second in the record. +

+

+This transformation of course has to be performed recursively, since +there can be several run-time variables in a parameter value: +

+
+    Ag np.n np.p
+
+

+A similar transformation would be possible to deal with the double +role of parameter records discussed above. Thus the type +

+
+    RNP = {n : Number ; p : Person}
+
+

+could be uniformly translated into the set {0,1,2,3,4,5} +as Agr above. Selections would be simple instances of indexing. +But any projection from the record should be translated into +a case expression, +

+
+    rnp.n  ===> 
+    case rnp of {
+      0 => 0 ;
+      1 => 0 ;
+      2 => 0 ;
+      3 => 1 ;
+      4 => 1 ;
+      5 => 1
+      }
+
+

+To avoid the code bloat resulting from this, we chose the alias representation +which is easy enough to deal with in interpreters. +

+ +

The representation of linearization types

+

+Linearization types (lincat) are not needed when generating with +GFCC, but they have been added to enable parser generation directly from +GFCC. The linearization type definitions are shown as a part of the +concrete syntax, by using terms to represent types. Here is the table +showing how different linearization types are encoded. +

+
+    P*                         = size(P)        -- parameter type              
+    {_ : I ; __ : R}*          = (I* @ R*)      -- record of parameters
+    {r1 : T1 ; ... ; rn : Tn}* = [T1*,...,Tn*]  -- other record
+    (P => T)*                  = [T* ,...,T*]   -- size(P) times
+    Str*                       = ()
+
+

+The category symbols are prefixed with two underscores (__). +For example, the linearization type present/CatEng.NP is +translated as follows: +

+
+    NP = {
+      a : {                     -- 6 = 2*3 values
+        n : {ParamX.Number} ;   -- 2 values
+        p : {ParamX.Person}     -- 3 values
+      } ;
+      s : {ResEng.Case} => Str  -- 3 values
+    }
+  
+    __NP = [(6@[2,3]),[(),(),()]]
+
+

+ +

Running the compiler and the GFCC interpreter

+

+GFCC generation is a part of the +developers' version +of GF since September 2006. To invoke the compiler, the flag +-printer=gfcc to the command +pm = print_multi is used. It is wise to recompile the grammar from +source, since previously compiled libraries may not obey the canonical +order of records. To strip the grammar before +GFCC translation removes unnecessary interface references. +Here is an example, performed in +example/bronzeage. +

+
+    i -src -path=.:prelude:resource-1.0/* -optimize=all_subs BronzeageEng.gf
+    i -src -path=.:prelude:resource-1.0/* -optimize=all_subs BronzeageGer.gf
+    strip
+    pm -printer=gfcc | wf bronze.gfcc
+
+

+ +

The reference interpreter

+

+The reference interpreter written in Haskell consists of the following files: +

+
+    -- source file for BNFC
+    GFCC.cf       -- labelled BNF grammar of gfcc
+  
+    -- files generated by BNFC
+    AbsGFCC.hs    -- abstrac syntax of gfcc
+    ErrM.hs       -- error monad used internally
+    LexGFCC.hs    -- lexer of gfcc files
+    ParGFCC.hs    -- parser of gfcc files and syntax trees
+    PrintGFCC.hs  -- printer of gfcc files and syntax trees
+  
+    -- hand-written files
+    DataGFCC.hs   -- post-parser grammar creation, linearization and evaluation
+    GenGFCC.hs    -- random and exhaustive generation, generate-and-test parsing
+    RunGFCC.hs    -- main function - a simple command interpreter
+
+

+It is included in the +developers' version +of GF, in the subdirectory GF/src/GF/Canon/GFCC. +

+

+To compile the interpreter, type +

+
+    make gfcc
+
+

+in GF/src. To run it, type +

+
+    ./gfcc <GFCC-file>
+
+

+The available commands are +

+ + + +

Interpreter in C++

+

+A base-line interpreter in C++ has been started. +Its main functionality is random generation of trees and linearization of them. +

+

+Here are some results from running the different interpreters, compared +to running the same grammar in GF, saved in .gfcm format. +The grammar contains the English, German, and Norwegian +versions of Bronzeage. The experiment was carried out on +Ubuntu Linux laptop with 1.5 GHz Intel centrino processor. +

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
GFgfcc(hs)gfcc++
program size7249k803k113k
grammar size336k119k119k
read grammar1150ms510ms100ms
generate 2229500ms450ms800ms
memory21M10M20M
+ +

+

+To summarize: +

+ + + +

Some things to do

+

+Interpreter in Java. +

+

+Parsing via MCFG +

+ + +

+Hand-written parsers for GFCC grammars to reduce code size +(and efficiency?) of interpreters. +

+

+Binary format and/or file compression of GFCC output. +

+

+Syntax editor based on GFCC. +

+

+Rewriting of resource libraries in order to exploit the +word-suffix sharing better (depth-one tables, as in FM). +

+ + + + -- cgit v1.2.3