@@ -2,34 +2,25 @@ module Control.IOExcept
22
33-- An IO monad with exception handling
44
5−data IOExcept : Type -> Type -> Type where
6− IOM : IO (Either err a) -> IOExcept err a
5+record IOExcept err a where
6+ constructor IOM
7+ runIOExcept : IO (Either err a)
78
89instance Functor (IOExcept e) where
910 map f (IOM fn) = IOM (map (map f) fn)
1011
1112instance Applicative (IOExcept e) where
1213 pure x = IOM (pure (pure x))
13− (IOM f) <*> (IOM a) = IOM (do f' <- f; a' <- a
14− return (f' <*> a'))
14+ (IOM f) <*> (IOM a) = IOM [| f <*> a |]
1515
1616instance Monad (IOExcept e) where
17− (IOM x) >>= k = IOM (do x' <- x;
18− case x' of
19− Right a => let (IOM ka) = k a in
20− ka
21− Left err => return (Left err))
17+ (IOM x) >>= f = IOM $ x >>= either (pure . Left) (runIOExcept . f)
2218
2319ioe_lift : IO a -> IOExcept err a
24−ioe_lift op = IOM (do op' <- op
25− return (Right op'))
20+ioe_lift op = IOM $ map Right op
2621
2722ioe_fail : err -> IOExcept err a
28−ioe_fail e = IOM (return (Left e))
23+ioe_fail e = IOM $ pure (Left e)
2924
3025ioe_run : IOExcept err a -> (err -> IO b) -> (a -> IO b) -> IO b
31−ioe_run (IOM act) err ok = do act' <- act
32− case act' of
33− Left e => err e
34− Right v => ok v
35−
26+ioe_run (IOM act) err ok = either err ok !act