better semantics and show div by zero errors earlier

[proglang.git] / Interpret.hs

diff --git a/Interpret.hs b/Interpret.hs
index 652e9793aaf2db2ca81bd396db3ef426e0d9d2ba..a674d1e509f04a2aa0ebb0d91c78300f453d6ead 100644 (file)
--- a/Interpret.hs
+++ b/Interpret.hs
@@ -28,7 +28,6 @@ interpret fun st = do
        runStateT (runErrorT  (do mapM addFunction fun; mapM_ execute st)) emptyState
        return ()
 
---eval :: (MonadState State m, MonadError String m, MonadIO m) => Exp -> m Value
 eval :: (MonadState State m, MonadIO m) => Exp -> EvalM m Value
 eval (EBool b) = return (VBool b)
 eval (EInt n) = return (VInt n)
@@ -40,7 +39,7 @@ eval (BiOpExp e o e') = do
        v <- eval e
        v'<- eval e'
        if elem o [Eq,NEq] then return $ opE o v v'
-               else let (VInt n1) = v in let (VInt n2) = v' in return $ op o n1 n2
+               else let (VInt n1) = v in let (VInt n2) = v' in return $! op o n1 n2
 eval (EPost i o) = do
        (VInt n) <- getVariableValue i
        setVariableValue i $ op o n 1
@@ -89,16 +88,17 @@ getNumber2 =  do
                else return ""
 
 -- op :: Op -> (a -> a -> Value)
-opE Eq = \e e' -> VBool $ e == e'
-opE NEq = \e e' -> VBool $ not (e == e')
-op Plus = \e e' -> VInt $ e + e'
-op Minus = \e e' -> VInt $ e - e'
-op Times = \e e' -> VInt $ e * e'
-op Div = \e e' -> VInt $ e `div` e'
-op Lt = \e e' -> VBool $ e < e'
-op ELt = \e e' -> VBool $ e <= e'
-op Gt = \e e' -> VBool $ e > e'
-op EGt = \e e' -> VBool $ e >= e'
+opE Eq e e' = VBool $ e == e'
+opE NEq e e' = VBool $ not (e == e')
+op Plus e e' =VInt $ e + e'
+op Minus e e' = VInt $ e - e'
+op Times e e' = VInt $ e * e'
+op Div _ 0 = error "Division by zero"
+op Div e e' = VInt $ e `div` e'
+op Lt e e' = VBool $ e < e'
+op ELt e e' = VBool $ e <= e'
+op Gt e e' = VBool $ e > e'
+op EGt e e' = VBool $ e >= e'
 
 getVariableValue :: (MonadState State m) => Ident -> m Value 
 getVariableValue i = do
@@ -124,7 +124,6 @@ pushAndPop s = do
        s
        modify (\s -> s { variables = tail $ variables s})
 
--- execute :: (MonadState Variables m) => Stm -> m ()
 execute :: (MonadState State m, MonadIO m) => Stm -> EvalM m ()
 execute (SNoop) = return ()
 execute (SExp e) = eval e >> return ()