18.08.2014, 23:16, "Konstantine Rybnikov"
The one that's below "main" is working properly, while the one on top of it gives this error:
typenats.hs:17:16: No instance for (Op D (0 + 1)) arising from a use of `f' Possible fix: add an instance declaration for (Op D (0 + 1)) In the expression: f (VJ i :: VJ D (0 + 1)) In an equation for `f': f (VJ i) = f (VJ i :: VJ D (0 + 1)) In the instance declaration for `Op D 0'
Hello Konstantine, I think you're using GHC 7.6.x series which had no solver for type-level natural numbers, resulting in 0+1 not typechecking with 1. You may find some history in https://ghc.haskell.org/trac/ghc/ticket/4385. With GHC 7.8 this compiles fine. Probably you can overcome the issue by providing the required instances of `+` type family by hand (up to the desired number), but it's hackish and may be tedious without TH. Just switch to 7.8 already.