whenJust vs. forM_ (Was: Add isLeft/isRight to Data.Either)

On Fri, 7 Dec 2012, Thomas Schilling wrote:

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

...

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.

Too much abstraction can certainly reduce readability. In this case I interpret Maybe as a list that can contain at most one element. This way I can use all the nice functions from Data.Foldable for Maybe.