remove unit type/value in favor of unit tuples

AST.hs

@@ -20,7 +20,6 @@ data AST = Add AST AST
 		 | Lambda [(Pattern, AST)]
 		 | Call AST AST
 		 | Access AST AST
-		 | UnitConst
 		 | Cons AST AST
 		 | IfExpr AST AST AST
 		 | TupleConst [AST]
@@ -34,7 +33,6 @@ data Pattern = VarP String
 			 | IntP Integer
 			 | StrP String
 			 | BoolP Bool
-			 | UnitP
 			 | ConsP Pattern Pattern
 			 | TupleP [Pattern]
 			 | ListP [Pattern]

Interp.hs

@@ -25,7 +25,6 @@ instance Ord BIF where compare a b = if a == b then EQ else LT
 
 data Value = IntV Integer
 		   | StrV String
-		   | UnitV
 		   | BoolV Bool
 		   | StreamV Int
 		   | TupleV [Value]
@@ -51,6 +50,7 @@ type Env = [M.Map String Value] -- lexical environment (linked list)
 type InterpState = StateT ([Handle], Env) IO -- interpreter state (open handles, global env)
 
 emptyEnv = [M.empty]
+unitv = TupleV []
 
 -- look up a binding from the bottom up
 lookup :: Env -> String -> Maybe Value
@@ -74,7 +74,6 @@ instance Show Value where
 	show (FnV _ _) = "<fn>"
 	show (StreamV _) = "<stream>"
 	show (Builtin _) = "<built-in>"
-	show UnitV = "()"
 
 -- value operators
 (IntV l) +$ (IntV r) = IntV (l + r)
@@ -106,13 +105,13 @@ _fputbytes (TupleV [StreamV h, StrV str]) = do
 	(handles,_) <- get
 	let handle = handles !! h
 	io <- lift $ hPutStr handle str
-	return UnitV
+	return unitv
 
 _fputstr (TupleV [StreamV h, StrV str]) = do
 	(handles,_) <- get
 	let handle = handles !! h
 	io <- lift $ hPutStr handle str
-	return UnitV
+	return unitv
 
 _fgetline (StreamV h) = do
 	(handles,_) <- get
@@ -148,7 +147,7 @@ _fclose handle@(StreamV h) = do
 	(handles,_) <- get
 	let handle = handles !! h
 	lift $ hClose handle
-	return UnitV
+	return unitv
 
 _sockopen (TupleV [StrV host, IntV port]) = do
 	(handles,env) <- get
@@ -163,7 +162,7 @@ _sockopen (TupleV [StrV host, IntV port]) = do
 
 _putstr str@(StrV _) = _fputstr $ TupleV [StreamV 0, str]
 _putbytes str@(StrV _) = _fputbytes $ TupleV [StreamV 0, str]
-_getline UnitV = _fgetline (StreamV 1)
+_getline (TupleV []) = _fgetline (StreamV 1)
 
 _print v = _putbytes $ StrV $ show v ++ "\n"
 _repr v = return . StrV $ show v
@@ -230,8 +229,6 @@ eval (IntConst i) = return $ IntV i
 eval (StrConst s) = return $ StrV s
 eval (BoolConst b) = return $ BoolV b
 
-eval UnitConst = return UnitV
-
 eval (Block body) = foldr1 (>>) $ map eval body
 
 eval (Cons a b) = do
@@ -338,9 +335,6 @@ patternBindings (BoolP b) (BoolV v)
 	| v == b = Just M.empty
 	| otherwise = Nothing
 
-patternBindings UnitP UnitV = Just M.empty
-patternBindings UnitP _ = Nothing
-
 patternBindings (StrP x) (StrV y)
 	| x == y = Just M.empty
 	| otherwise = Nothing

Lamb.hs

@@ -7,7 +7,7 @@ import System.Directory (doesFileExist)
 import System.FilePath (FilePath, splitExtension)
 import Control.Monad.IO.Class (liftIO)
 import Parser (parseProgram)
-import Interp (evalFileV, evalProgram, initIO, interpret, InterpState, Value(UnitV))
+import Interp (evalFileV, evalProgram, initIO, interpret, InterpState, Value)
 
 -- returns Nothing if all files exist, or Just path for the first one that doesn't
 allExist :: [FilePath] -> IO (Maybe FilePath)

Parser.hs

@@ -1,6 +1,7 @@
 {-# Language TemplateHaskell, QuasiQuotes, FlexibleContexts #-}
 
 module Parser where
+import Data.Maybe (fromMaybe)
 import Text.Peggy hiding (space)
 import AST
 
@@ -21,9 +22,7 @@ semistatements :: [AST]
 
 args :: AST
   = expr ("," expr)+ { TupleConst ($1 : $2) }
-  / expr? { case $1 of
+  / expr? { fromMaybe (TupleConst []) $1 } 
-  				Just x -> x
-  				Nothing -> UnitConst }
 
 patternlist :: Pattern
   = pattern ("," pattern)+ { ListP ($1 : $2) }
@@ -47,9 +46,7 @@ pattern :: Pattern
 
 funpattern :: Pattern
   = pattern ("," pattern)+ { TupleP ($1 : $2) }
-  / pattern? { case $1 of
+  / pattern? { fromMaybe (TupleP []) $1 }
-  					Just x -> x
-  					Nothing -> UnitP }
 
 listseq :: AST
   = expr ("," expr)+ { ListConst ($1 : $2) }