Diagonally in Data.Bimap

[Joachim Breitner]

Hi

Am Donnerstag, den 05.07.2018, 15:36 +0200 schrieb Gabor Greif:
> Hi!
> 
> Just searched for a `bimap` variant that simultaneously transforms
> both components with the same morphism:
> 
> ``` haskell
> diag :: Bifunctor p => (a -> b) -> p a a -> p b b
> diag f = bimap f f
> ```
> 
> I did not find any. Would it make sense to add it?

possibly, I have wanted it too before.

Bikeshedding:
I’d have expected the name “both”. It also has precedence here:
http://hackage.haskell.org/package/extra/docs/Data-Tuple-Extra.html#v:both
http://hackage.haskell.org/package/concatenative/docs/Control-Concatenative.html#v:both
http://hackage.haskell.org/package/MissingK/docs/Control-Arrow-Extra.html#v:both
http://hackage.haskell.org/package/lens-family/docs/Lens-Family2-Stock.html#v:both
http://hackage.haskell.org/package/lens/docs/Control-Lens-Traversal.html#v:both

Diagonally sounds more like something of type `a -> (a,a)` or similar.

> PPS: I would have sent this to libraries at haskell.org but it seem to be
> closed group.

It should not. Maybe only open to subscribers? (A common crude anti-
spam measurement.)

Cheers,
Joachim


-- 
Joachim Breitner
  mail at joachim-breitner.de
  http://www.joachim-breitner.de/
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