Ord overview

The Ord type class represents types which support comparisons with a total order.

Instances should satisfy the laws of total orderings:

  1. Reflexivity: S.compare(a, a) <= 0
  2. Antisymmetry: if S.compare(a, b) <= 0 and S.compare(b, a) <= 0 then a <-> b
  3. Transitivity: if S.compare(a, b) <= 0 and S.compare(b, c) <= 0 then S.compare(a, c) <= 0

Added in v2.0.0


Table of contents


Contravariant

contramap

Signature

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

Added in v2.0.0

combinators

getDualOrd

Signature

export declare function getDualOrd<A>(O: Ord<A>): Ord<A>

Added in v2.0.0

constructors

fromCompare

Signature

export declare function fromCompare<A>(compare: (x: A, y: A) => Ordering): Ord<A>

Added in v2.0.0

instances

URI

Signature

export declare const URI: 'Ord'

Added in v2.0.0

URI (type alias)

Signature

export type URI = typeof URI

Added in v2.0.0

contravariantOrd

Signature

export declare const contravariantOrd: Contravariant1<'Ord'>

Added in v2.7.0

getMonoid

Returns a Monoid such that:

  • its concat(ord1, ord2) operation will order first by ord1, and then by ord2
  • its empty value is an Ord that always considers compared elements equal

Signature

export declare function getMonoid<A = never>(): Monoid<Ord<A>>

Example

import { sort } from 'fp-ts/lib/Array'
import { contramap, getDualOrd, getMonoid, ordBoolean, ordNumber, ordString } from 'fp-ts/lib/Ord'
import { pipe } from 'fp-ts/lib/function'
import { fold } from 'fp-ts/lib/Monoid'

interface User {
  id: number
  name: string
  age: number
  rememberMe: boolean
}

const byName = pipe(
  ordString,
  contramap((p: User) => p.name)
)

const byAge = pipe(
  ordNumber,
  contramap((p: User) => p.age)
)

const byRememberMe = pipe(
  ordBoolean,
  contramap((p: User) => p.rememberMe)
)

const M = getMonoid<User>()

const users: Array<User> = [
  { id: 1, name: 'Guido', age: 47, rememberMe: false },
  { id: 2, name: 'Guido', age: 46, rememberMe: true },
  { id: 3, name: 'Giulio', age: 44, rememberMe: false },
  { id: 4, name: 'Giulio', age: 44, rememberMe: true },
]

// sort by name, then by age, then by `rememberMe`
const O1 = fold(M)([byName, byAge, byRememberMe])
assert.deepStrictEqual(sort(O1)(users), [
  { id: 3, name: 'Giulio', age: 44, rememberMe: false },
  { id: 4, name: 'Giulio', age: 44, rememberMe: true },
  { id: 2, name: 'Guido', age: 46, rememberMe: true },
  { id: 1, name: 'Guido', age: 47, rememberMe: false },
])

// now `rememberMe = true` first, then by name, then by age
const O2 = fold(M)([getDualOrd(byRememberMe), byName, byAge])
assert.deepStrictEqual(sort(O2)(users), [
  { id: 4, name: 'Giulio', age: 44, rememberMe: true },
  { id: 2, name: 'Guido', age: 46, rememberMe: true },
  { id: 3, name: 'Giulio', age: 44, rememberMe: false },
  { id: 1, name: 'Guido', age: 47, rememberMe: false },
])

Added in v2.4.0

getTupleOrd

Given a tuple of Ords returns an Ord for the tuple

Signature

export declare function getTupleOrd<T extends ReadonlyArray<Ord<any>>>(
  ...ords: T
): Ord<{ [K in keyof T]: T[K] extends Ord<infer A> ? A : never }>

Example

import { getTupleOrd, ordString, ordNumber, ordBoolean } from 'fp-ts/lib/Ord'

const O = getTupleOrd(ordString, ordNumber, ordBoolean)
assert.strictEqual(O.compare(['a', 1, true], ['b', 2, true]), -1)
assert.strictEqual(O.compare(['a', 1, true], ['a', 2, true]), -1)
assert.strictEqual(O.compare(['a', 1, true], ['a', 1, false]), 1)

Added in v2.0.0

ordBoolean

Signature

export declare const ordBoolean: Ord<boolean>

Added in v2.0.0

ordDate

Signature

export declare const ordDate: Ord<Date>

Added in v2.0.0

ordNumber

Signature

export declare const ordNumber: Ord<number>

Added in v2.0.0

ordString

Signature

export declare const ordString: Ord<string>

Added in v2.0.0

getSemigroup

Use getMonoid instead

Signature

export declare function getSemigroup<A = never>(): Semigroup<Ord<A>>

Added in v2.0.0

ord

Signature

export declare const ord: Contravariant1<'Ord'>

Added in v2.0.0

type classes

Ord (interface)

Signature

export interface Ord<A> extends Eq<A> {
  readonly compare: (x: A, y: A) => Ordering
}

Added in v2.0.0

utils

between

Test whether a value is between a minimum and a maximum (inclusive)

Signature

export declare function between<A>(O: Ord<A>): (low: A, hi: A) => (x: A) => boolean

Added in v2.0.0

clamp

Clamp a value between a minimum and a maximum

Signature

export declare function clamp<A>(O: Ord<A>): (low: A, hi: A) => (x: A) => A

Added in v2.0.0

geq

Test whether one value is non-strictly greater than another

Signature

export declare function geq<A>(O: Ord<A>): (x: A, y: A) => boolean

Added in v2.0.0

gt

Test whether one value is strictly greater than another

Signature

export declare function gt<A>(O: Ord<A>): (x: A, y: A) => boolean

Added in v2.0.0

leq

Test whether one value is non-strictly less than another

Signature

export declare function leq<A>(O: Ord<A>): (x: A, y: A) => boolean

Added in v2.0.0

lt

Test whether one value is strictly less than another

Signature

export declare function lt<A>(O: Ord<A>): (x: A, y: A) => boolean

Added in v2.0.0

max

Take the maximum of two values. If they are considered equal, the first argument is chosen

Signature

export declare function max<A>(O: Ord<A>): (x: A, y: A) => A

Added in v2.0.0

min

Take the minimum of two values. If they are considered equal, the first argument is chosen

Signature

export declare function min<A>(O: Ord<A>): (x: A, y: A) => A

Added in v2.0.0