kcsongor/typelevel-prelude

feature request - add functor application ($)

Closed this issue · 4 comments

srghma commented

hi, I see you added functor composition (.) type family, is it possible to make functor application?

kcsongor commented

Done!

srghma commented

awesome

I even added link to your repo in my old stackowerflow question https://stackoverflow.com/questions/52791746/how-to-make-dot-composition-and-dollar-application-sign-for-functors

Can I have a few questions :

  • what is ->{m} thingy?
  • when this become available in haskell officially? )
kcsongor commented

Sure!

The details are available in the paper, but here's the gist:

This library works with a fork of GHC with UnsaturatedTypeFamilies. To avoid the issues of partially applying type families, this branch assigns different kinds to type constructors and type families, based on whether they're "matchable" or "unmatchable" respectively. The ->{m} syntax
is thus a matchability polymorphic arrow that accepts either type constructors of type families as arguments (with m being a matchability type variable).

To answer the second question, I'm currently writing a proposal for GHC about this feature -- if that proposal gets accepted, then the feature will be added to GHC.

  • 👍1
srghma commented

ok, tnx, looking forward to the day when haskell become agda