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 True) = "1"
13 show (VBool False) = "0"
15 type Variables = [Map Ident Value]
17 inList :: Eq a => a -> [a] -> Bool
19 inList a (x:xs) = if a == x then True else inList a xs
21 --eval :: (MonadState Variables m) => Exp -> m Value
22 eval :: Exp -> StateT Variables IO Value
23 eval (EBool b) = return (VBool b)
24 eval (EInt n) = return (VInt n)
25 eval (EVar i) = getVariableValue i
26 eval (EAss i e) = setVariableValue i e
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
33 (VInt n) <- getVariableValue i
34 let (VInt n') = op o n 1 in setVariableValue i $ EInt n'
41 return $ VBool $ not b
44 return $ VInt $ read s
47 return $ VBool $ if (read s == 0) then False else True
52 if inList c [' ', '\n', '\t', '\r']
58 -- op :: Op -> (a -> a -> Value)
59 opE Eq = \e e' -> VBool $ e == e'
60 opE NEq = \e e' -> VBool $ not (e == e')
61 op Plus = \e e' -> VInt $ e + e'
62 op Minus = \e e' -> VInt $ e - e'
63 op Times = \e e' -> VInt $ e * e'
64 op Div = \e e' -> VInt $ e `div` e'
65 op Lt = \e e' -> VBool $ e < e'
66 op ELt = \e e' -> VBool $ e <= e'
67 op Gt = \e e' -> VBool $ e > e'
68 op EGt = \e e' -> VBool $ e >= e'
70 getVariableValue :: (MonadState Variables m) => Ident -> m Value
71 getVariableValue i = do
75 findVariable :: (MonadState Variables m) => Ident -> Variables -> m Value
76 findVariable i [] = fail $ "Variable "++show i++" not found in any scope."
77 findVariable i (m:ms) = if member i m then lookup i m else findVariable i ms
79 --setVariableValue :: (MonadState Variables m) => Ident -> Exp -> m Value
80 --setVariableValue :: (MonadState Variables m) => Ident -> Exp -> m Value
82 setVariableValue :: Ident -> Exp -> StateT Variables IO Value
83 setVariableValue i e = do
86 put $ updateVariable i v ms
89 updateVariable :: Ident -> Value -> Variables -> Variables
90 updateVariable _ _ [] = []
91 updateVariable i v (m:ms) = if member i m then insert i v m:ms else m:updateVariable i v ms
93 pushAndPop :: (MonadState Variables m) => m a -> m ()
99 -- execute :: (MonadState Variables m) => Stm -> m ()
100 execute :: Stm -> StateT Variables IO ()
101 execute (SNoop) = return ()
102 execute (SExp e) = eval e >> return ()
103 execute (SIf b s s') = do
105 pushAndPop $ if b' then execute s else execute s'
106 execute (SPrint e) = do
109 execute (SBlock ss) = pushAndPop $ mapM execute ss
110 execute (SWhile e s) = do
112 if b then pushAndPop (execute s) >> execute (SWhile e s) else return ()
113 execute (SDeclD t i) = execute $ SDecl t i $ case t of
116 execute (SDecl t i e) =do
119 put $ (insert i v m):ms