Existential type that can be constrained.

This library provides utilities for working with existential types and type-level constraints. It allows you to enforce multiple constraints on polymorphic types and containers complementing the package some.

constrained-some

This library provides utilities for working with existential types and type-level constraints. It allows you to enforce multiple constraints on polymorphic types and containers complementing some.

Core

• Existential types: Somes and Somes1 provide existential wrappers for types with multiple constraints.
• Convenient aliases: Simplified types Some and Some1 for scenarios where just one constraint is needed.
• More convenient aliases: Simplified types SomeF and SomesF for scenarios where the container of a Somes1 is known.
• Natural transformations with constraints
  • mapSome :: (forall a. AllC csa a => f a -> g a) -> SomesF f csa -> SomesF g csa
  • traverseSome :: Functor m => (forall a. AllC csa a => f a -> m (g a)) -> SomesF f csa -> m (SomesF g csa)

Usage

import Data.Some.Constraint

someShowableOrd :: Somes '[Show, Ord]
someShowableOrd = Some [1, 2, 3 :: Int]

someNumFunctor :: Some1 Functor Num
someNumFunctor = Some1 [1, 2, 3 :: Int]

someListShowable :: SomeF [] Show
someListShowable = Some1 [1, 2, 3 :: Int]

Contact information

Contributions, critics and bug reports are welcome!

Please feel free to contact me through GitHub.