eval (EInt n) = return (VInt n)
eval (EVar i) = getVariableValue i
eval (EAss i e) = setVariableValue i e
-eval EDefault = error "EDefault called from an illegal place"
eval (BiOpExp e o e') = do
v <- eval e
v'<- eval e'
--setVariableValue :: (MonadState Variables m) => Ident -> Exp -> m Value
--setVariableValue :: (MonadState Variables m) => Ident -> Exp -> m Value
-addVariable :: Ident -> Exp -> StateT Variables IO ()
-addVariable i e = do
- e' <- eval e
- (m:ms) <- get
- put $ (insert i e' m):ms
setVariableValue :: Ident -> Exp -> StateT Variables IO Value
setVariableValue i e = do
updateVariable _ _ [] = []
updateVariable i v (m:ms) = if member i m then insert i v m:ms else m:updateVariable i v ms
+pushAndPop :: (MonadState Variables m) => m a -> m ()
+pushAndPop s = do
+ modify (empty:)
+ s
+ modify tail
-- execute :: (MonadState Variables m) => Stm -> m ()
execute :: Stm -> StateT Variables IO ()
execute (SExp e) = eval e >> return ()
execute (SIf b s s') = do
(VBool b') <- eval b
- if b' then execute s else execute s'
+ pushAndPop $ if b' then execute s else execute s'
execute (SPrint e) = do
e' <- eval e
lift $ print e'
-execute (SBlock ss) = do
- modify (empty:)
- mapM execute ss
- modify tail
+execute (SBlock ss) = pushAndPop $ mapM execute ss
execute (SWhile e s) = do
(VBool b) <- eval e
- if b then execute s >> execute (SWhile e s) else return ()
-execute (SDecl t i EDefault) = do
- case t of
- TInt -> addVariable i (EInt 0)
- TBool -> addVariable i (EBool False)
- return ()
-execute (SDecl t i e) = addVariable i e >> return ()
+ if b then pushAndPop (execute s) >> execute (SWhile e s) else return ()
+execute (SDeclD t i) = execute (SDecl t i $ case t of
+ TInt -> EInt 0
+ TBool -> EBool False
+ )
+execute (SDecl t i e) =do
+ e' <- eval e
+ (m:ms) <- get
+ put $ (insert i e' m):ms