1 module Interpret (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 True) = "1"
13 show (VBool False) = "0"
15 type Variables = [Map Ident Value]
17 interpret :: [Stm] -> IO ()
18 interpret s = runStateT (mapM execute s) [empty] >> return ()
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 (BiOpExp e o e') = do
29 if elem o [Eq,NEq] then return $ opE o v v'
30 else let (VInt n1) = v in let (VInt n2) = v' in return $ op o n1 n2
32 (VInt n) <- getVariableValue i
33 let (VInt n') = op o n 1 in setVariableValue i $ EInt n'
40 return $ VBool $ not b
43 return $ VInt $ read s
46 return $ VBool $ if (read s == 0) then False else True
51 if elem c [' ', '\n', '\t', '\r']
57 -- op :: Op -> (a -> a -> Value)
58 opE Eq = \e e' -> VBool $ e == e'
59 opE NEq = \e e' -> VBool $ not (e == e')
60 op Plus = \e e' -> VInt $ e + e'
61 op Minus = \e e' -> VInt $ e - e'
62 op Times = \e e' -> VInt $ e * e'
63 op Div = \e e' -> VInt $ e `div` e'
64 op Lt = \e e' -> VBool $ e < e'
65 op ELt = \e e' -> VBool $ e <= e'
66 op Gt = \e e' -> VBool $ e > e'
67 op EGt = \e e' -> VBool $ e >= e'
69 getVariableValue :: (MonadState Variables m) => Ident -> m Value
70 getVariableValue i = do
74 findVariable :: (MonadState Variables m) => Ident -> Variables -> m Value
75 findVariable i [] = fail $ "Variable "++show i++" not found in any scope."
76 findVariable i (m:ms) = if member i m then lookup i m else findVariable i ms
78 --setVariableValue :: (MonadState Variables m) => Ident -> Exp -> m Value
79 --setVariableValue :: (MonadState Variables m) => Ident -> Exp -> m Value
81 setVariableValue :: Ident -> Exp -> StateT Variables IO Value
82 setVariableValue i e = do
85 put $ updateVariable i v ms
88 updateVariable :: Ident -> Value -> Variables -> Variables
89 updateVariable _ _ [] = []
90 updateVariable i v (m:ms) = if member i m then insert i v m:ms else m:updateVariable i v ms
92 pushAndPop :: (MonadState Variables m) => m a -> m ()
98 -- execute :: (MonadState Variables m) => Stm -> m ()
99 execute :: Stm -> StateT Variables IO ()
100 execute (SNoop) = return ()
101 execute (SExp e) = eval e >> return ()
102 execute (SIf b s s') = do
104 pushAndPop $ if b' then execute s else execute s'
105 execute (SPrint e) = do
108 execute (SBlock ss) = pushAndPop $ mapM execute ss
109 execute (SWhile e s) = do
111 if b then pushAndPop (execute s) >> execute (SWhile e s) else return ()
112 execute (SDeclD t i) = execute $ SDecl t i $ case t of
115 execute (SDecl t i e) =do
118 put $ (insert i v m):ms