Difference between revisions of "Restrict type of monadic binding"
From HaskellWiki
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(types of other monadic functions) |
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| Line 5: | Line 5: | ||
</haskell> | </haskell> | ||
This way, you can omit <hask> _ <- </hask> only if the monadic return value has type <hask> () </hask>. | This way, you can omit <hask> _ <- </hask> only if the monadic return value has type <hask> () </hask>. | ||
| + | |||
| + | Types of some other monadic operations should be restricted, too. | ||
| + | <haskell> | ||
| + | mapM_ :: Monad m => (a -> m ()) -> [a] -> m () | ||
| + | replicateM_ :: Monad m => Int -> m () -> m () | ||
| + | sequence_ :: Monad m => [m ()] -> m () | ||
| + | zipWithM_ :: Monad m => (a -> b -> m ()) -> [a] -> [b] -> m () | ||
| + | </haskell> | ||
[[Category:Proposals]] | [[Category:Proposals]] | ||
Revision as of 16:09, 9 November 2007
According to Do notation considered harmful#Safety the type of the monadic binding combinator (>>) should be restricted to
(>>) :: m () -> m a -> m a
This way, you can omit _ <- only if the monadic return value has type ().
Types of some other monadic operations should be restricted, too.
mapM_ :: Monad m => (a -> m ()) -> [a] -> m ()
replicateM_ :: Monad m => Int -> m () -> m ()
sequence_ :: Monad m => [m ()] -> m ()
zipWithM_ :: Monad m => (a -> b -> m ()) -> [a] -> [b] -> m ()