r28760@phanatique: nelhage | 2007-12-20 21:21:10 -0800

 move Expression into its own module


git-svn-id: svn+ssh://lunatique.mit.edu/data/svn/flnv/trunk@28 e7f7c2cb-1e20-0410-8c26-a6ba679ee1f5

FLNV/AST.hs

@@ -1,13 +1,14 @@
 module FLNV.AST where
 
 import FLNV.Error
-import FLNV.Parser (Expression(..))
+import FLNV.Expression
 import Control.Monad
 
 -- An AST is approximately an Expression, but it makes special forms
 -- and calls explicit. Syntax checking occurs during the translation
 -- from Expression to AST
-data AST = Lambda [String] AST
+data AST = Define String Expression
+         | Lambda [String] AST
          | If AST AST AST
          | Apply AST [AST]
          | AString String

FLNV/Error.hs

@@ -5,14 +5,16 @@ import Text.ParserCombinators.Parsec (ParseError)
 import Control.Monad.Error (throwError, MonadError)
 import qualified Control.Monad.Error as E
 
-import {-# SOURCE #-} FLNV.Parser (Expression)
+import FLNV.Expression
 
 data Error = Error String
            | ReadErr ParseError
            | SyntaxError String Expression
+           | InternalError String
+           | Undefined String
+           | DuplicateBinding String
              deriving Show
 
 instance E.Error Error where
     noMsg = Error "An error has occurred"
     strMsg = Error
-

FLNV/Expression.hs

@@ -0,0 +1,26 @@
+module FLNV.Expression (Expression(..)) where
+
+data Expression = Symbol String
+                | Number Integer
+                | String String
+                | Bool Bool
+                | Cons Expression Expression
+                | Nil
+                  deriving (Eq)
+
+instance Show Expression where
+    show (Symbol s) = s
+    show (Number n) = show n
+    show (String s) = '"' : s ++ "\""
+    show (Bool True) = "#t"
+    show (Bool False) = "#f"
+    show c@(Cons a b) = "(" ++ showListInner c ++ ")"
+    show Nil = "()"
+
+showListInner :: Expression -> String
+showListInner (Cons a b@(Cons _ _)) = show a ++ " " ++ showListInner b
+showListInner (Cons a Nil) = show a
+showListInner (Cons a b) = show a ++ " . " ++ showListInner b
+showListInner Nil = ""
+showListInner x = show x
+

FLNV/Parser.hs

@@ -1,33 +1,10 @@
-module FLNV.Parser (Expression(..), readExpr) where
+module FLNV.Parser (readExpr) where
 
+import FLNV.Expression
 import FLNV.Error
 import Control.Monad
 import Text.ParserCombinators.Parsec hiding (newline)
 
-data Expression = Symbol String
-                | Number Integer
-                | String String
-                | Bool Bool
-                | Cons Expression Expression
-                | Nil
-                  deriving (Eq)
-
-instance Show Expression where
-    show (Symbol s) = s
-    show (Number n) = show n
-    show (String s) = '"' : s ++ "\""
-    show (Bool True) = "#t"
-    show (Bool False) = "#f"
-    show c@(Cons a b) = "(" ++ showListInner c ++ ")"
-    show Nil = "()"
-
-showListInner :: Expression -> String
-showListInner (Cons a b@(Cons _ _)) = show a ++ " " ++ showListInner b
-showListInner (Cons a Nil) = show a
-showListInner (Cons a b) = show a ++ " . " ++ showListInner b
-showListInner Nil = ""
-showListInner x = show x
-
 readExpr :: (MonadError Error m) => String -> m Expression
 readExpr s = case parse sExpression "scheme" s of
                Left err -> throwError $ ReadErr err