Proposal: Add bool to Data.Bool

[Dag Odenhall]

+1, I‘ve often wanted this but don’t want to add a dependency just for bool,
so I end up writing it myself, locally in a where every time, which doesn't
feel very Haskelly to do!

I would even like it in Prelude, but I expect that to get much more
opposition so this proposal should probably not discuss that possibility at
all.


On Wed, Sep 11, 2013 at 12:02 AM, Oliver Charles <ollie at ocharles.org.uk>wrote:

> Hello,
>
> I would like to propose that the following is added to Data.Bool in base:
>
> bool :: a -> a -> Bool -> a
> bool f _ False = f
> bool _ t True  = t
>
> (Aka, bool f t b = if b then t else f)
>
> The purpose of this is hopefully evident from its definition. I find
> myself reaching for this in cases similar to where I would use 'maybe' -
> often when I'm working with 'fmap' and don't want to start introducing
> names for the function I am using to map over some functor.
>
> I suggested this in #haskell and other people also seem frustrated this
> doesn't exist, and would like to see it happen - hopefully they will
> voice their support as a reply here.
>
> A quick search on FPComplete's Hoogle [1] shows five equivalent
> functions on the first page - and I'm sure there are more on subsequent
> pages.
>
> Thoughts?
> - ocharles
>
> ---
> [1]:
>
> https://www.fpcomplete.com/hoogle?q=Bool+-%3E+a+-%3E+a+-%3E+a&env=ghc-7.4.2-stable-13.09
>
>
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