Control.Lens.Internal.Coerce

This module provides a shim around coerce. We need to work around a GHC 7.8-specific Coercible solver bug(s).

Documentation

coerce :: forall (k :: RuntimeRep) (a :: TYPE k) (b :: TYPE k). Coercible a b => a -> b

The function coerce allows you to safely convert between values of types that have the same representation with no run-time overhead. In the simplest case you can use it instead of a newtype constructor, to go from the newtype's concrete type to the abstract type. But it also works in more complicated settings, e.g. converting a list of newtypes to a list of concrete types.

This function is runtime-representation polymorphic, but the RuntimeRep type argument is marked as Inferred, meaning that it is not available for visible type application. This means the typechecker will accept coerce @Int @Age 42.

coerce' :: forall a b. Coercible a b => b -> a

(#..) :: (Profunctor p, Coercible c b) => (b -> c) -> p a b -> p a c