Some more documentation

2 files changed, 21 insertions, 14 deletions

diff --git a/src-3.0/PGF.hs b/src-3.0/PGF.hs
index fafbfafcf..899d26d12 100644
--- a/src-3.0/PGF.hs
+++ b/src-3.0/PGF.hs
@@ -5,7 +5,11 @@
 -- Stability   : stable
 -- Portability : portable
 --
--- Application Programming Interface to PGF.
+-- This module is an Application Programming Interface to 
+-- to load and interpret grammars compiled Portable Grammar Format (PGF).
+-- The PGF format is produced as a final output from the GF compiler.
+-- The API is meant to be used when embedding GF grammars in Haskell 
+-- programs.
 -------------------------------------------------
 
 module PGF(
@@ -24,7 +28,7 @@ module PGF(
            Category, categories, startCat,
 
            -- * Expressions
-           Exp(..),
+           Exp(..), Equation(..),
            showExp, readExp,
 
            -- * Operations
@@ -61,10 +65,6 @@ import qualified Text.PrettyPrint as PP
 import qualified Text.ParserCombinators.ReadP as RP
 
 
--- This API is meant to be used when embedding GF grammars in Haskell 
--- programs. The embedded system is supposed to use the
--- .pgf grammar format, which is first produced by the gf program.
-
 ---------------------------------------------------
 -- Interface
 ---------------------------------------------------
diff --git a/src-3.0/PGF/Data.hs b/src-3.0/PGF/Data.hs
index 95ea2e1a7..95db1fedf 100644
--- a/src-3.0/PGF/Data.hs
+++ b/src-3.0/PGF/Data.hs
@@ -42,15 +42,18 @@ data Type =
    DTyp [Hypo] CId [Exp]
   deriving (Eq,Ord,Show)
 
+-- | An expression representing the abstract syntax tree
+-- in PGF. The same expression is used in the dependent
+-- types.
 data Exp =
-   EAbs [CId] Exp
- | EApp CId [Exp]
- | EStr   String
- | EInt   Integer
- | EFloat Double
- | EMeta  Integer
- | EVar   CId
- | EEq [Equation]
+   EAbs [CId] Exp                   -- ^ lambda abstraction. The list should contain at least one variable
+ | EApp CId [Exp]                   -- ^ application. Note that unevaluated lambda abstractions are not allowed
+ | EStr   String                    -- ^ string constant
+ | EInt   Integer                   -- ^ integer constant
+ | EFloat Double                    -- ^ floating point constant
+ | EMeta  Integer                   -- ^ meta variable
+ | EVar   CId                       -- ^ variable reference
+ | EEq [Equation]                   -- ^ lambda function defined as a set of equations with pattern matching
   deriving (Eq,Ord,Show)
 
 data Term =
@@ -79,6 +82,10 @@ data Hypo =
    Hyp CId Type
   deriving (Eq,Ord,Show)
 
+-- | The equation is used to define lambda function as a sequence
+-- of equations with pattern matching. The list of 'Exp' represents
+-- the patterns and the second 'Exp' is the function body for this
+-- equation.
 data Equation =
    Equ [Exp] Exp
   deriving (Eq,Ord,Show)