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Restrict type of monadic binding

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(part of "do notation considered harmful" which can be seen as a proposal)
 
(+essay tag; should be obvious, since it's in the proposals cat, but...)
 
(2 intermediate revisions by one user not shown)
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According to [[Do_notation_considered_harmful#Safety]]
+
{{essay}}
  +
  +
According to [[Do notation considered harmful#Safety]]
 
the type of the monadic binding combinator (>>) should be restricted to
 
the type of the monadic binding combinator (>>) should be restricted to
 
<haskell>
 
<haskell>
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</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.
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<haskell>
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mapM_ :: Monad m => (a -> m ()) -> [a] -> m ()
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replicateM_ :: Monad m => Int -> m () -> m ()
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sequence_ :: Monad m => [m ()] -> m ()
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zipWithM_ :: Monad m => (a -> b -> m ()) -> [a] -> [b] -> m ()
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</haskell>
   
 
[[Category:Proposals]]
 
[[Category:Proposals]]

Latest revision as of 13:37, 12 June 2009

This page addresses an aspect of Haskell style, which is to some extent a matter of taste. Just pick what you find appropriate for you and ignore the rest.

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 ()