Skip to main content Link Search Menu Expand Document (external link)
core

Predicate overview

Added in v1.0.0

Table of contents

combinators

and

Combines two predicates into a new predicate that returns true if both of the predicates returns true.

Signature

export declare const and: {
  <A>(that: Predicate<A>): (self: Predicate<A>) => Predicate<A>
  <A>(self: Predicate<A>, that: Predicate<A>): Predicate<A>
}

Example

import * as P from '@fp-ts/core/Predicate'

const minLength = (n: number) => (s: string) => s.length >= n
const maxLength = (n: number) => (s: string) => s.length <= n

const length = (n: number) => P.and(minLength(n), maxLength(n))

assert.deepStrictEqual(length(2)('aa'), true)
assert.deepStrictEqual(length(2)('a'), false)
assert.deepStrictEqual(length(2)('aaa'), false)

Added in v1.0.0

not

Negates the result of a given predicate.

Signature

export declare const not: <A>(self: Predicate<A>) => Predicate<A>

Example

import * as P from '@fp-ts/core/Predicate'
import * as N from '@fp-ts/core/Number'

const isPositive = P.not(N.lessThan(0))

assert.deepStrictEqual(isPositive(-1), false)
assert.deepStrictEqual(isPositive(0), true)
assert.deepStrictEqual(isPositive(1), true)

Added in v1.0.0

or

Combines two predicates into a new predicate that returns true if at least one of the predicates returns true.

Signature

export declare const or: {
  <A>(that: Predicate<A>): (self: Predicate<A>) => Predicate<A>
  <A>(self: Predicate<A>, that: Predicate<A>): Predicate<A>
}

Example

import * as P from '@fp-ts/core/Predicate'
import * as N from '@fp-ts/core/Number'

const nonZero = P.or(N.lessThan(0), N.greaterThan(0))

assert.deepStrictEqual(nonZero(-1), true)
assert.deepStrictEqual(nonZero(0), false)
assert.deepStrictEqual(nonZero(1), true)

Added in v1.0.0

constructors

contramap

Given a Predicate<A> returns a Predicate<B>

Signature

export declare const contramap: {
  <B, A>(f: (b: B) => A): (self: Predicate<A>) => Predicate<B>
  <A, B>(self: Predicate<A>, f: (b: B) => A): Predicate<B>
}

Example

import * as P from '@fp-ts/core/Predicate'
import * as N from '@fp-ts/core/Number'

const minLength3 = P.contramap(N.greaterThan(2), (s: string) => s.length)

assert.deepStrictEqual(minLength3('a'), false)
assert.deepStrictEqual(minLength3('aa'), false)
assert.deepStrictEqual(minLength3('aaa'), true)
assert.deepStrictEqual(minLength3('aaaa'), true)

Added in v1.0.0

do notation

Do

Signature

export declare const Do: Predicate<{}>

Added in v1.0.0

andThenBind

A variant of bind that sequentially ignores the scope.

Signature

export declare const andThenBind: {
  <N extends string, A extends object, B>(name: Exclude<N, keyof A>, that: Predicate<B>): (
    self: Predicate<A>
  ) => Predicate<{ readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
  <A extends object, N extends string, B>(
    self: Predicate<A>,
    name: Exclude<N, keyof A>,
    that: Predicate<B>
  ): Predicate<{ readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
}

Added in v1.0.0

bindTo

Signature

export declare const bindTo: {
  <N extends string>(name: N): <A>(self: Predicate<A>) => Predicate<{ readonly [K in N]: A }>
  <A, N extends string>(self: Predicate<A>, name: N): Predicate<{ readonly [K in N]: A }>
}

Added in v1.0.0

guards

isBigint

Tests if a value is a bigint.

Signature

export declare const isBigint: (input: unknown) => input is bigint

Example

import { isBigint } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isBigint(1n), true)

assert.deepStrictEqual(isBigint(1), false)

Added in v1.0.0

isBoolean

Tests if a value is a boolean.

Signature

export declare const isBoolean: (input: unknown) => input is boolean

Example

import { isBoolean } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isBoolean(true), true)

assert.deepStrictEqual(isBoolean('true'), false)

Added in v1.0.0

isDate

A guard that succeeds when the input is a Date.

Signature

export declare const isDate: (input: unknown) => input is Date

Example

import { isDate } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isDate(new Date()), true)

assert.deepStrictEqual(isDate(null), false)
assert.deepStrictEqual(isDate({}), false)

Added in v1.0.0

isError

A guard that succeeds when the input is an Error.

Signature

export declare const isError: (input: unknown) => input is Error

Example

import { isError } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isError(new Error()), true)

assert.deepStrictEqual(isError(null), false)
assert.deepStrictEqual(isError({}), false)

Added in v1.0.0

isFunction

Tests if a value is a function.

Signature

export declare const isFunction: (input: unknown) => input is Function

Example

import { isFunction } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isFunction(isFunction), true)

assert.deepStrictEqual(isFunction('function'), false)

Added in v1.0.0

isNever

A guard that always fails.

Signature

export declare const isNever: (input: unknown) => input is never

Example

import { isNever } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isNever(null), false)
assert.deepStrictEqual(isNever(undefined), false)
assert.deepStrictEqual(isNever({}), false)
assert.deepStrictEqual(isNever([]), false)

Added in v1.0.0

isNotNull

Tests if a value is not undefined.

Signature

export declare const isNotNull: <A>(input: A) => input is Exclude<A, null>

Example

import { isNotNull } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isNotNull(undefined), true)
assert.deepStrictEqual(isNotNull('null'), true)

assert.deepStrictEqual(isNotNull(null), false)

Added in v1.0.0

isNotNullable

A guard that succeeds when the input is not null or undefined.

Signature

export declare const isNotNullable: <A>(input: A) => input is NonNullable<A>

Example

import { isNotNullable } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isNotNullable({}), true)
assert.deepStrictEqual(isNotNullable([]), true)

assert.deepStrictEqual(isNotNullable(null), false)
assert.deepStrictEqual(isNotNullable(undefined), false)

Added in v1.0.0

isNotUndefined

Tests if a value is not undefined.

Signature

export declare const isNotUndefined: <A>(input: A) => input is Exclude<A, undefined>

Example

import { isNotUndefined } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isNotUndefined(null), true)
assert.deepStrictEqual(isNotUndefined('undefined'), true)

assert.deepStrictEqual(isNotUndefined(undefined), false)

Added in v1.0.0

isNull

Tests if a value is undefined.

Signature

export declare const isNull: (input: unknown) => input is null

Example

import { isNull } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isNull(null), true)

assert.deepStrictEqual(isNull(undefined), false)
assert.deepStrictEqual(isNull('null'), false)

Added in v1.0.0

isNullable

A guard that succeeds when the input is null or undefined.

Signature

export declare const isNullable: <A>(input: A) => input is Extract<A, null | undefined>

Example

import { isNullable } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isNullable(null), true)
assert.deepStrictEqual(isNullable(undefined), true)

assert.deepStrictEqual(isNullable({}), false)
assert.deepStrictEqual(isNullable([]), false)

Added in v1.0.0

isNumber

Tests if a value is a number.

Signature

export declare const isNumber: (input: unknown) => input is number

Example

import { isNumber } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isNumber(2), true)

assert.deepStrictEqual(isNumber('2'), false)

Added in v1.0.0

isObject

Tests if a value is an object.

Signature

export declare const isObject: (input: unknown) => input is object

Example

import { isObject } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isObject({}), true)
assert.deepStrictEqual(isObject([]), true)

assert.deepStrictEqual(isObject(null), false)
assert.deepStrictEqual(isObject(undefined), false)

Added in v1.0.0

isReadonlyRecord

A guard that succeeds when the input is a readonly record.

Signature

export declare const isReadonlyRecord: (input: unknown) => input is {}

Example

import { isReadonlyRecord } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isReadonlyRecord({}), true)
assert.deepStrictEqual(isReadonlyRecord({ a: 1 }), true)

assert.deepStrictEqual(isReadonlyRecord([]), false)
assert.deepStrictEqual(isReadonlyRecord([1, 2, 3]), false)
assert.deepStrictEqual(isReadonlyRecord(null), false)
assert.deepStrictEqual(isReadonlyRecord(undefined), false)

Added in v1.0.0

isRecord

A guard that succeeds when the input is a record.

Signature

export declare const isRecord: (input: unknown) => input is {}

Example

import { isRecord } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isRecord({}), true)
assert.deepStrictEqual(isRecord({ a: 1 }), true)

assert.deepStrictEqual(isRecord([]), false)
assert.deepStrictEqual(isRecord([1, 2, 3]), false)
assert.deepStrictEqual(isRecord(null), false)
assert.deepStrictEqual(isRecord(undefined), false)

Added in v1.0.0

isString

Tests if a value is a string.

Signature

export declare const isString: (input: unknown) => input is string

Example

import { isString } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isString('a'), true)

assert.deepStrictEqual(isString(1), false)

Added in v1.0.0

isSymbol

Tests if a value is a symbol.

Signature

export declare const isSymbol: (input: unknown) => input is symbol

Example

import { isSymbol } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isSymbol(Symbol.for('a')), true)

assert.deepStrictEqual(isSymbol('a'), false)

Added in v1.0.0

isUndefined

Tests if a value is undefined.

Signature

export declare const isUndefined: (input: unknown) => input is undefined

Example

import { isUndefined } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isUndefined(undefined), true)

assert.deepStrictEqual(isUndefined(null), false)
assert.deepStrictEqual(isUndefined('undefined'), false)

Added in v1.0.0

isUnknown

A guard that always succeeds.

Signature

export declare const isUnknown: (input: unknown) => input is unknown

Example

import { isUnknown } from '@fp-ts/core/Predicate'

assert.deepStrictEqual(isUnknown(null), true)
assert.deepStrictEqual(isUnknown(undefined), true)

assert.deepStrictEqual(isUnknown({}), true)
assert.deepStrictEqual(isUnknown([]), true)

Added in v1.0.0

instances

Contravariant

Signature

export declare const Contravariant: contravariant.Contravariant<PredicateTypeLambda>

Added in v1.0.0

Invariant

Signature

export declare const Invariant: invariant.Invariant<PredicateTypeLambda>

Added in v1.0.0

Of

Signature

export declare const Of: of_.Of<PredicateTypeLambda>

Added in v1.0.0

Product

Signature

export declare const Product: product_.Product<PredicateTypeLambda>

Added in v1.0.0

SemiProduct

Signature

export declare const SemiProduct: semiProduct.SemiProduct<PredicateTypeLambda>

Added in v1.0.0

getMonoidAll

Signature

export declare const getMonoidAll: <A>() => monoid.Monoid<Predicate<A>>

Added in v1.0.0

getMonoidAny

Signature

export declare const getMonoidAny: <A>() => monoid.Monoid<Predicate<A>>

Added in v1.0.0

getSemigroupAll

Signature

export declare const getSemigroupAll: <A>() => semigroup.Semigroup<Predicate<A>>

Added in v1.0.0

getSemigroupAny

Signature

export declare const getSemigroupAny: <A>() => semigroup.Semigroup<Predicate<A>>

Added in v1.0.0

models

Predicate (interface)

Signature

export interface Predicate<A> {
  (a: A): boolean
}

Added in v1.0.0

Refinement (interface)

Signature

export interface Refinement<A, B extends A> {
  (a: A): a is B
}

Added in v1.0.0

type lambdas

PredicateTypeLambda (interface)

Signature

export interface PredicateTypeLambda extends TypeLambda {
  readonly type: Predicate<this['Target']>
}

Added in v1.0.0

utils

all

Signature

export declare const all: <A>(collection: Iterable<Predicate<A>>) => Predicate<A>

Added in v1.0.0

any

Signature

export declare const any: <A>(collection: Iterable<Predicate<A>>) => Predicate<A>

Added in v1.0.0

appendElement

This function appends a predicate to a tuple-like predicate, allowing you to create a new predicate that includes the original elements and the new one.

Signature

export declare const appendElement: {
  <A extends readonly any[], B>(self: Predicate<A>, that: Predicate<B>): Predicate<readonly [...A, B]>
  <B>(that: Predicate<B>): <A extends readonly any[]>(self: Predicate<A>) => Predicate<readonly [...A, B]>
}

Added in v1.0.0

compose

Signature

export declare const compose: {
  <A, B extends A, C extends B>(bc: Refinement<B, C>): (ab: Refinement<A, B>) => Refinement<A, C>
  <A, B extends A, C extends B>(ab: Refinement<A, B>, bc: Refinement<B, C>): Refinement<A, C>
}

Added in v1.0.0

of

Signature

export declare const of: <A>(_: A) => Predicate<A>

Added in v1.0.0

struct

Signature

export declare const struct: <R extends Record<string, Predicate<any>>>(
  predicates: R
) => Predicate<{ readonly [K in keyof R]: [R[K]] extends [Predicate<infer A>] ? A : never }>

Added in v1.0.0

tuple

Similar to Promise.all but operates on Predicates.

[Predicate<A>, Predicate<B>, ...] -> Predicate<[A, B, ...]>

Signature

export declare const tuple: <T extends readonly Predicate<any>[]>(
  ...predicates: T
) => Predicate<Readonly<{ [I in keyof T]: [T[I]] extends [Predicate<infer A>] ? A : never }>>

Added in v1.0.0

tupled

Signature

export declare const tupled: <A>(self: Predicate<A>) => Predicate<readonly [A]>

Added in v1.0.0

unit

Signature

export declare const unit: Predicate<void>

Added in v1.0.0