From 89a4c9c8d8cb07f4fb749316fa20534708073b62 Mon Sep 17 00:00:00 2001
From: Michael Andreen <harv@ruin.nu>
Date: Wed, 15 Mar 2006 16:20:05 +0000
Subject: [PATCH] better semantics and show div by zero errors earlier

---
 Interpret.hs  | 25 ++++++++++++-------------
 documentation | 14 +++++++++++++-
 2 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/Interpret.hs b/Interpret.hs
index 652e979..a674d1e 100644
--- 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 ()
diff --git a/documentation b/documentation
index 9127c08..196220a 100644
--- a/documentation
+++ b/documentation
@@ -72,7 +72,7 @@ Evaluate the arguments in order, find function definition, remove the old variab
 
 [SReturn]
 
-<return e,c> <= <e,c> => <v,c'>, c'[ret->v], STOP
+<return e,c> => c'[ret->v] <= <e,c> => <v,c'>
 
 Evaluate the expression, add the value as return value to the state and stop the execution of the state
 
@@ -87,3 +87,15 @@ Adds the function i with parameters ds and body ss to the context
 <fs ss, c> => c'' <= c[fs] => c', <ss,c'> => c''
 
 Add all the function to the context and execute the statements in this context
+
+[SEQ]
+
+<s1;s2,c> => c' <= <s1,c> => c', c'(ret)
+
+If the context returned by s1 contains a return-value, return this context without executing the next statement.
+
+[SWhile]
+
+<while e s,c> => c''' => <e,c> => <true,c'> push(c') => c'' <s,c''> => c''', c'''(ret)
+
+If the context returned by the body contains a return-value, return this context and don't try to run the loop again.
-- 
2.39.2