whenJust / forM_ (was Re: Proposal: Add isLeft/isRight to Data.Either)

On 8 December 2012 02:38, Erik Hesselink wrote:

On Friday, December 7, 2012, Thomas Schilling wrote:

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On 7 December 2012 09:25, Erik Hesselink wrote:

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There is no need to define whenJust, since it is just a specialization of forM_ from Data.Foldable.

I don't know if that's such a good argument. I prefer my code readable -- too much abstraction can have a seriously bad effect on that. As a simple rule, if the user has to do type inference in their head, readability suffers.

In this case, "forM_" implies we're iterating over something container like, "whenJust" means "I want to do something if this thing yielded a result". It depends on the context whether a "Maybe" is behaving more container-like or is indicating the presence of a result where there may not have been one.

I don't have this problem, but I guess that's just personal. But in general I'm not in favor of adding specialized versions of generalized functions.

indeed, and likewise we should get rid of Control.Monad.forM_ :: Monad m => [a] -> (a -> m b) -> m () which is just the same specialization to lists (and likely the reason that forM_ doesn't come to mind for other container types, as much as I generally like Data.Foldable). btw: $ git grep whenJust|wc -l 40 Conrad.