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

2009/7/18 Edward Kmett :

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