fp-ts

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Overview

The Plus type class extends the alt type class with a value that should be the left and right identity for alt.

It is similar to Monoid, except that it applies to types of kind * -> *, like Array or Option, rather than concrete types like string or number.

Plus instances should satisfy the following laws:

  1. Left identity: A.alt(zero, fa) == fa
  2. Right identity: A.alt(fa, zero) == fa
  3. Annihilation: A.map(zero, fa) == zero

Table of contents

Plus (interface)

Signature

export interface Plus<F> extends Alt<F> {
  readonly zero: <A>() => HKT<F, A>
}

Added in v1.0.0

Plus1 (interface)

Signature

export interface Plus1<F extends URIS> extends Alt1<F> {
  readonly zero: <A>() => Type<F, A>
}

Plus2 (interface)

Signature

export interface Plus2<F extends URIS2> extends Alt2<F> {
  readonly zero: <L, A>() => Type2<F, L, A>
}

Plus2C (interface)

Signature

export interface Plus2C<F extends URIS2, L> extends Alt2C<F, L> {
  readonly zero: <A>() => Type2<F, L, A>
}

Plus3 (interface)

Signature

export interface Plus3<F extends URIS3> extends Alt3<F> {
  readonly zero: <U, L, A>() => Type3<F, U, L, A>
}

Plus3C (interface)

Signature

export interface Plus3C<F extends URIS3, U, L> extends Alt3C<F, U, L> {
  readonly zero: <A>() => Type3<F, U, L, A>
}