Eq.md

• Eq interface
• Built-in primitive eqs
• Combinators

Eq interface

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

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

Example

import { Eq } from 'fp-ts/Eq'

export const string: Eq<string> = {
  equals: (x, y) => x === y
}

Built-in primitive eqs

• string: Eq<string>
• number: Eq<number>
• boolean: Eq<boolean>
• UnknownArray: Eq<Array<unknown>>
• UnknownRecord: Eq<Record<string, unknown>>

Combinators

• literal
• nullable
• type
• partial
• record
• array
• tuple
• intersection
• sum
• lazy

Example

import * as E from 'io-ts/Eq'

const Person = E.type({
  name: E.string,
  age: E.number
})

console.log(Person.equals({ name: 'a', age: 0 }, { name: 'a', age: 0 })) // => true
console.log(Person.equals({ name: 'a', age: 0 }, { name: '', age: 0 })) // => false
console.log(Person.equals({ name: 'a', age: 0 }, { name: 'a', age: 1 })) // => false