1 module Interpret (eval, execute, Value(VInt, VBool)) where
4 import Control.Monad.State
6 import Prelude hiding (lookup)
8 data Value = VInt Integer | VBool Bool deriving Eq
10 instance Show Value where
11 show (VInt n) = show n
12 show (VBool b) = show b
14 type Variables = [Map Ident Value]
16 inList :: Eq a => a -> [a] -> Bool
18 inList a (x:xs) = if a == x then True else inList a xs
20 --eval :: (MonadState Variables m) => Exp -> m Value
21 eval :: Exp -> StateT Variables IO Value
22 eval (EBool b) = return (VBool b)
23 eval (EInt n) = return (VInt n)
24 eval (EVar i) = getVariableValue i
25 eval (EAss i e) = setVariableValue i e
26 eval EDefault = return (VInt 0) --FIXME!!!
27 eval (BiOpExp e o e') = do
30 if inList o [Eq,NEq] then return $ opE o v v'
31 else let (VInt n1) = v in let (VInt n2) = v' in return $ op o n1 n2
32 typeCheckExp (EPost i op) = do
33 (VInt n) <- getVariableValue i
34 setVariableValue i $ EInt $ n+1
37 -- op :: Op -> (a -> a -> Value)
38 opE Eq = \e e' -> VBool $ e == e'
39 opE NEq = \e e' -> VBool $ not (e == e')
40 op Plus = \e e' -> VInt $ e + e'
41 op Minus = \e e' -> VInt $ e - e'
42 op Times = \e e' -> VInt $ e * e'
43 op Div = \e e' -> VInt $ e `div` e'
45 getVariableValue :: (MonadState Variables m) => Ident -> m Value
46 getVariableValue i = do
50 --setVariableValue :: (MonadState Variables m) => Ident -> Exp -> m Value
51 setVariableValue :: Ident -> Exp -> StateT Variables IO Value
52 setVariableValue i e = do
55 put $ (insert i e' m):ms
58 findVariable :: (MonadState Variables m) => Ident -> Variables -> m Value
59 findVariable i [] = fail $ "Variable "++show i++" not found in any scope."
60 findVariable i (m:ms) = if member i m then lookup i m else findVariable i ms
62 -- execute :: (MonadState Variables m) => Stm -> m ()
63 execute :: Stm -> StateT Variables IO ()
64 execute (SIf b s s') = do
66 if b' then execute s else execute s'
67 execute (SPrint e) = do
70 execute (SNoop) = return ()
71 execute (SBlock ss) = do
75 execute (SWhile e s) = do
77 if b then execute (SWhile e s) else return ()
78 execute (SDecl t i EDefault) = do
80 TInt -> setVariableValue i (EInt 0)
81 TBool -> setVariableValue i (EBool False)
83 execute (SDecl t i e) = setVariableValue i e >> return ()