Proposal: Add isLeft/isRight to Data.Either

Thomas Schilling nominolo at
Fri Dec 7 18:14:13 CET 2012

On 7 December 2012 09:25, Erik Hesselink <hesselink at> 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.

 / Thomas

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