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 = error "EDefault called from an illegal place"
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 $ read s
52 if inList c ['\n','\r',' ', '\t']
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
81 addVariable :: Ident -> Exp -> StateT Variables IO ()
85 put $ (insert i e' m):ms
87 setVariableValue :: Ident -> Exp -> StateT Variables IO Value
88 setVariableValue i e = do
91 put $ updateVariable i v ms
94 updateVariable :: Ident -> Value -> Variables -> Variables
95 updateVariable _ _ [] = []
96 updateVariable i v (m:ms) = if member i m then insert i v m:ms else m:updateVariable i v ms
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 if b' then execute s else execute s'
106 execute (SPrint e) = do
109 execute (SBlock ss) = do
113 execute (SWhile e s) = do
115 if b then execute s >> execute (SWhile e s) else return ()
116 execute (SDecl t i EDefault) = do
118 TInt -> addVariable i (EInt 0)
119 TBool -> addVariable i (EBool False)
121 execute (SDecl t i e) = addVariable i e >> return ()