added the expression type

src/runtime/haskell/PGF2/Expr.hsc

@@ -1,6 +1,66 @@
 #include <pgf/pgf.h>
 
-module PGF2.Expr where
+module PGF2.Expr(Var, Cat, Fun,
+                 BindType(..), Literal(..), Expr(..),
+                 Type(..), Hypo,
+                 Patt(..), Equation(..)
+                ) where
 
+type Var = String -- ^ Name of syntactic category
 type Cat = String -- ^ Name of syntactic category
 type Fun = String -- ^ Name of function
+
+type MetaId = Int
+
+data BindType = 
+    Explicit
+  | Implicit
+  deriving (Eq,Ord,Show)
+
+data Literal =
+   LStr String                      -- ^ string constant
+ | LInt Int                         -- ^ integer constant
+ | LFlt Double                      -- ^ floating point constant
+ deriving (Eq,Ord,Show)
+
+-- | An expression in the abstract syntax of the grammar. It could be
+-- both parameter of a dependent type or an abstract syntax tree for
+-- for some sentence.
+data Expr =
+   EAbs BindType Var Expr           -- ^ lambda abstraction
+ | EApp Expr Expr                   -- ^ application
+ | ELit Literal                     -- ^ literal
+ | EMeta  {-# UNPACK #-} !MetaId    -- ^ meta variable
+ | EFun   Fun                       -- ^ function or data constructor
+ | EVar   {-# UNPACK #-} !Int       -- ^ variable with de Bruijn index
+ | ETyped Expr Type                 -- ^ local type signature
+ | EImplArg Expr                    -- ^ implicit argument in expression
+  deriving (Eq,Ord,Show)
+
+-- | To read a type from a 'String', use 'readType'.
+data Type =
+   DTyp [Hypo] Cat [Expr]
+  deriving (Eq,Ord,Show)
+
+-- | 'Hypo' represents a hypothesis in a type i.e. in the type A -> B, A is the hypothesis
+type Hypo = (BindType,Var,Type)
+
+
+-- | The pattern is used to define equations in the abstract syntax of the grammar.
+data Patt =
+   PApp Fun [Patt]                  -- ^ application. The identifier should be constructor i.e. defined with 'data'
+ | PLit Literal                     -- ^ literal
+ | PVar Var                         -- ^ variable
+ | PAs  Var Patt                    -- ^ variable@pattern
+ | PWild                            -- ^ wildcard
+ | PImplArg Patt                    -- ^ implicit argument in pattern
+ | PTilde Expr
+  deriving Show
+
+-- | The equation is used to define lambda function as a sequence
+-- of equations with pattern matching. The list of 'Expr' represents
+-- the patterns and the second 'Expr' is the function body for this
+-- equation.
+data Equation =
+   Equ [Patt] Expr
+  deriving Show