Data.Parameterized.Compose

Utilities for working with Data.Functor.Compose.

NB: This module contains an orphan instance. It will be included in GHC 8.10, see https://gitlab.haskell.org/ghc/ghc/merge_requests/273 and also https:/github.comhaskell-compatbase-orphansissues/49.

Documentation

testEqualityComposeBare :: forall k l (f :: k -> Type) (g :: l -> k) x y. (forall w z. f w -> f z -> Maybe (w :~: z)) -> Compose f g x -> Compose f g y -> Maybe (x :~: y)

The deduction (via generativity) that if g x :~: g y then x :~: y.

See https://gitlab.haskell.org/ghc/ghc/merge_requests/273.