Added Read and Show instances for Type. This required moving some code around.

src/PGF/Expr.hs

@@ -1,4 +1,7 @@
-module PGF.Expr(readTree, showTree, pTree, ppTree,
+module PGF.Expr(Tree(..), Literal(..),                
+                readTree, showTree, pTree, ppTree,
+
+                Expr(..), Equation(..),
                 readExpr, showExpr, pExpr, ppExpr,
 
                 tree2expr, expr2tree,
@@ -11,7 +14,6 @@ module PGF.Expr(readTree, showTree, pTree, ppTree,
                ) where
 
 import PGF.CId
-import PGF.Data
 
 import Data.Char
 import Data.Maybe
@@ -20,6 +22,45 @@ import qualified Text.PrettyPrint as PP
 import qualified Text.ParserCombinators.ReadP as RP
 import qualified Data.Map as Map
 
+data Literal = 
+   LStr String                      -- ^ string constant
+ | LInt Integer                     -- ^ integer constant
+ | LFlt Double                      -- ^ floating point constant
+ deriving (Eq,Ord,Show)
+
+-- | The tree is an evaluated expression in the abstract syntax
+-- of the grammar. The type is especially restricted to not
+-- allow unapplied lambda abstractions. The tree is used directly 
+-- from the linearizer and is produced directly from the parser.
+data Tree = 
+   Abs [CId] Tree                   -- ^ lambda abstraction. The list of variables is non-empty
+ | Var CId                          -- ^ variable
+ | Fun CId [Tree]                   -- ^ function application
+ | Lit Literal                      -- ^ literal
+ | Meta Int                         -- ^ meta variable
+  deriving (Show, Eq, Ord)
+
+-- | An expression represents a potentially unevaluated expression
+-- in the abstract syntax of the grammar. It can be evaluated with
+-- the 'expr2tree' function and then linearized or it can be used
+-- directly in the dependent types.
+data Expr =
+   EAbs CId Expr                    -- ^ lambda abstraction
+ | EApp Expr Expr                   -- ^ application
+ | ELit Literal                     -- ^ literal
+ | EMeta  Int                       -- ^ meta variable
+ | EVar   CId                       -- ^ variable or function reference
+ | EEq [Equation]                   -- ^ lambda function defined as a set of equations with pattern matching
+ | EPi CId Expr Expr                -- ^ dependent function type
+  deriving (Eq,Ord,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 [Expr] Expr
+  deriving (Eq,Ord,Show)
 
 -- | parses 'String' as an expression
 readTree :: String -> Maybe Tree