effect-io-ai

Package: effect
Module: Either

Either.liftPredicate

Transforms a Predicate function into a Right of the input value if the predicate returns true or Left of the result of the provided function if the predicate returns false

Example

import * as assert from "node:assert"
import { pipe, Either } from "effect"

const isPositive = (n: number): boolean => n > 0
const isPositiveEither = Either.liftPredicate(isPositive, n => `${n} is not positive`)

assert.deepStrictEqual(
  isPositiveEither(1),
  Either.right(1)
)
assert.deepStrictEqual(
  isPositiveEither(0),
  Either.left("0 is not positive")
)

Signature

declare const liftPredicate: { <A, B extends A, E>(refinement: Refinement<A, B>, orLeftWith: (a: A) => E): (a: A) => Either<B, E>; <B extends A, E, A = B>(predicate: Predicate<A>, orLeftWith: (a: A) => E): (a: B) => Either<B, E>; <A, E, B extends A>(self: A, refinement: Refinement<A, B>, orLeftWith: (a: A) => E): Either<B, E>; <B extends A, E, A = B>(self: B, predicate: Predicate<A>, orLeftWith: (a: A) => E): Either<B, E>; }

Source

Since v3.4.0