On Fri, 13 Jan 2023, rowan goemans wrote:
I'm a heavy user of ghc-typelits-natnormalise.
I can feel your pain that it sometimes isn't able to solve seemingly "simple" constraints. But not all is lost in those cases. The `constraints` package allows one to solve `Nat` constraints out of thin air, provided you go through a function to do it.
nLEZeroIsZeroRule :: (n <= 0) :- (n ~ 0) nLEZeroIsZeroRule = Sub (unsafeCoerce (Dict :: Dict (a ~ a)))
Good to know that there are ways to add missing transformations. Ideally there would be a way without unsafeCoerce, i.e. that I could prove a property manually using some proof steps expressed in functions. Alternatively, maybe I can write missing steps in a custom type checker plugin. Has someone already tried to connect SBV to a type checker plugin?