Newtype

Lean: Hale.Base.Newtype | Haskell: Data.Monoid / Data.Semigroup

Overview

Monoid/semigroup wrappers: Dual, Endo, First, Last, Sum, Product, All, Any. Each wraps a value and provides an Append instance with specific combining semantics.

API Mapping

Lean	Haskell	Kind
`Dual`	`Dual`	Wrapper
`Endo`	`Endo`	Wrapper
`First`	`First`	Wrapper
`Last`	`Last`	Wrapper
`Sum` / `Sum.getSum`	`Sum` / `getSum`	Wrapper
`Product` / `Product.getProduct`	`Product` / `getProduct`	Wrapper
`All`	`All`	Wrapper
`Any`	`Any`	Wrapper

Instances

All wrappers provide Append.

Wrapper	`BEq`	`Ord`	`Repr`	`Hashable`	`ToString`
`Dual`	yes	yes	yes	yes	yes
`Sum`	yes	yes	yes	yes	yes
`Product`	yes	yes	yes	yes	yes
`All`	yes	yes	yes	yes	yes
`Any`	yes	yes	yes	yes	yes
`First`	yes	—	yes	—	yes
`Last`	yes	—	yes	—	yes
`Endo`	—	—	—	—	—

Proofs & Guarantees

append_assoc — associativity of Append for each wrapper

Example

-- Sum combines via addition
Sum.mk 3 ++ Sum.mk 4
-- => Sum 7