[Haskell-cafe] (liftM join .) . mapM

[Kim-Ee Yeoh]

I'd write it as

foo f = join .<$> sequence . (f <$>)

where
(.<$>) :: (.<$>) :: Functor f => (a -> b) -> ((x -> f a) -> (x -> f b))
x .<$> y = (x <$>) . y

is part of my line-noise toolbox.

This join .* sequence family of functions is quite common. 
Should really have a name for them.



Tony Morris-4 wrote:
> 
> Can (liftM join .) . mapM be improved?
> (Monad m) => (a -> m [b]) -> [a] -> m [b]
> 

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