I have to admit that is a heck of a lot easier to use than what I have: https://github.com/ekmett/constraints/blob/master/src/Data/Constraint/Nat.hs =) -Edward On Wed, Aug 17, 2016 at 9:11 AM, Christiaan Baaij < christiaan.baaij@gmail.com> wrote:

Hi,

If you have ever worked with `GHC.TypeLits`, then you have probably encountered an error very similar to:

...

• Could not deduce (KnownNat (n + 2)) arising from a use of ‘natVal’ from the context: KnownNat n

i.e. where GHC cannot infer a `KnownNat (n+2)` constraint, even though a `KnownNat n` constraint is already given.

Enter http://hackage.haskell.org/package/ghc-typelits-knownnat A type-checker plugin that can automatically derive "complex" KnownNat constraints from simpler ones.

To use it, you simply add the

{-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}

pragma to the top of your file.

If you want to know more, you can also check out the corresponding blog posts:

http://qbaylogic.com/blog/2016/08/10/solving-knownnat-constr aints-plugin.html http://qbaylogic.com/blog/2016/08/17/solving-knownnat-custom -operations.html

Regards,

Christiaan _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.