effect-io-ai

Package: effect
Module: Option

Option.exists

Checks whether the value in a Some satisfies a predicate or refinement.

When to use

Use to check a condition on an optional value without unwrapping

Details

• None → false
• Some where predicate(value) is true → true
• Some where predicate(value) is false → false
• With a refinement, narrows the Option type on true

Example (Testing a condition)

import { Option } from "effect"

const isEven = (n: number) => n % 2 === 0

console.log(Option.some(2).pipe(Option.exists(isEven)))
// Output: true

console.log(Option.some(1).pipe(Option.exists(isEven)))
// Output: false

console.log(Option.none().pipe(Option.exists(isEven)))
// Output: false

See

• filter to keep or discard based on a predicate
• contains to test for a specific value

Signature

declare const exists: { <A, B extends A>(refinement: Refinement<NoInfer<A>, B>): (self: Option<A>) => self is Option<B>; <A>(predicate: Predicate<NoInfer<A>>): (self: Option<A>) => boolean; <A, B extends A>(self: Option<A>, refinement: Refinement<A, B>): self is Option<B>; <A>(self: Option<A>, predicate: Predicate<A>): boolean; }

Source

Since v2.0.0