Compose

Lean: Hale.Base.Compose | Haskell: Data.Functor.Compose

Overview

Composition of functors/applicatives. Compose F G a wraps F (G a), allowing two functors to be composed into a single functor (or two applicatives into a single applicative).

API Mapping

Instances

• Functor (Compose F G) (requires Functor F, Functor G)
• Pure (Compose F G) (requires Applicative F, Applicative G)
• Seq (Compose F G) (requires Applicative F, Applicative G)
• Applicative (Compose F G) (requires Applicative F, Applicative G)

Proofs & Guarantees

• map_id — Functor.map id = id (with lawful functors)
• map_comp — Functor.map (f . g) = Functor.map f . Functor.map g (with lawful functors)

Example

-- Compose List and Option into a single functor
Compose.mk [some 1, none, some 3]
-- : Compose List Option Nat