Haskell Foldable Wats

Kosyrev Serge _deepfire at feelingofgreen.ru
Thu Feb 25 22:28:27 UTC 2016

Edward Kmett <ekmett at gmail.com> writes:
> It is actually quite fundamental.
> Instance resolution works on pattern matching on the type and we need
> all instances to be "global" and not able to be hidden or locally
> overridden to avoid coherence problems.
> There have been attempts to relax this restriction in the past, none
> of which are particularly satisfactory. 
> * http://dspace.library.uu.nl/handle/1874/294072 is probably the most
> recent, but some are quite old.

Thank you for the education!

> But basically all of them have run afoul of other ways to get "stuck"
> when resolving instances, or needing a vocabulary to track provenance
> of instances, or violate the open world assumptions. 

To my undeducated guess, the paper appears to do a decent job on
covering the alternatives.

One thing changed since that paper -- type families gained injectivity,
the lack of which was listed as the issue with the associated type families

Barring the (huge) question of it changing the kind of Functor, are
there any other problems with it?

с уважениeм / respectfully,
Косырев Сергей

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