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Eq overview

The Eq type class represents types which support decidable equality.

Instances must satisfy the following laws:

  1. Reflexivity: E.equals(a, a) === true
  2. Symmetry: E.equals(a, b) === E.equals(b, a)
  3. Transitivity: if E.equals(a, b) === true and E.equals(b, c) === true, then E.equals(a, c) === true

Added in v2.0.0


Table of contents


Contravariant

contramap

Signature

export declare const contramap: <A, B>(f: (b: B) => A) => (fa: Eq<A>) => Eq<B>

Added in v2.0.0

combinators

struct

Signature

export declare const struct: <A>(eqs: { [K in keyof A]: Eq<A[K]> }) => Eq<{ readonly [K in keyof A]: A[K] }>

Added in v2.10.0

tuple

Given a tuple of Eqs returns a Eq for the tuple

Signature

export declare const tuple: <A extends readonly unknown[]>(...eqs: { [K in keyof A]: Eq<A[K]> }) => Eq<Readonly<A>>

Example

import { tuple } from 'fp-ts/Eq'
import * as S from 'fp-ts/string'
import * as N from 'fp-ts/number'
import * as B from 'fp-ts/boolean'

const E = tuple(S.Eq, N.Eq, B.Eq)
assert.strictEqual(E.equals(['a', 1, true], ['a', 1, true]), true)
assert.strictEqual(E.equals(['a', 1, true], ['b', 1, true]), false)
assert.strictEqual(E.equals(['a', 1, true], ['a', 2, true]), false)
assert.strictEqual(E.equals(['a', 1, true], ['a', 1, false]), false)

Added in v2.10.0

getStructEq

Use struct instead.

Signature

export declare const getStructEq: <O extends Readonly<Record<string, any>>>(eqs: { [K in keyof O]: Eq<O[K]> }) => Eq<O>

Added in v2.0.0

getTupleEq

Use tuple instead.

Signature

export declare const getTupleEq: <T extends readonly Eq<any>[]>(
  ...eqs: T
) => Eq<{ [K in keyof T]: T[K] extends Eq<infer A> ? A : never }>

Added in v2.0.0

constructors

fromEquals

Signature

export declare const fromEquals: <A>(equals: (x: A, y: A) => boolean) => Eq<A>

Added in v2.0.0

instances

Contravariant

Signature

export declare const Contravariant: Contravariant1<'Eq'>

Added in v2.7.0

URI

Signature

export declare const URI: 'Eq'

Added in v2.0.0

URI (type alias)

Signature

export type URI = typeof URI

Added in v2.0.0

eqStrict

Signature

export declare const eqStrict: Eq<unknown>

Added in v2.5.0

getMonoid

Signature

export declare const getMonoid: <A>() => Monoid<Eq<A>>

Added in v2.6.0

getSemigroup

Signature

export declare const getSemigroup: <A>() => Semigroup<Eq<A>>

Added in v2.10.0

eqBoolean

Use Eq instead.

Signature

export declare const eqBoolean: Eq<boolean>

Added in v2.0.0

eqDate

Use Eq instead.

Signature

export declare const eqDate: Eq<Date>

Added in v2.0.0

eqNumber

Use Eq instead.

Signature

export declare const eqNumber: Eq<number>

Added in v2.0.0

eqString

Use Eq instead.

Signature

export declare const eqString: Eq<string>

Added in v2.0.0

eq

Use small, specific instances instead.

Signature

export declare const eq: Contravariant1<'Eq'>

Added in v2.0.0

type classes

Eq (interface)

Signature

export interface Eq<A> {
  readonly equals: (x: A, y: A) => boolean
}

Added in v2.0.0

utils

strictEqual

Use eqStrict instead

Signature

export declare const strictEqual: <A>(a: A, b: A) => boolean

Added in v2.0.0