[Haskell-cafe] Why is there no Zippable class? Would this work?

porges at porg.es porges at porg.es
Fri Jul 17 22:37:34 EDT 2009

2009/7/18 Edward Kmett <ekmett at gmail.com>:
> I wrote a short blog post on this:
> http://comonad.com/reader/2008/zipping-and-unzipping-functors/
> and one on the less powerful dual operations (less powerful because while
> every Haskell Functor is strong, much fewer are costrong):
> http://comonad.com/reader/2008/cozipping/
> -Edward Kmett

This is getting a bit OT, but I just wanted to comment that attempting to remove polymorphism from the Functor class (see thread a couple of days ago) means that not every Functor is strong. So strength for Functor would seem to require a fully polymorphic type. I don't know if costrength is 'easier' to derive for those 'restricted' Functors...

- George
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