effect-io-ai

Package: effect
Module: Predicate

Predicate.Refinement

A predicate that also narrows the input type when it returns true.

When to use

Use when you want a runtime check that refines A to B for TypeScript, especially when composing type guards with compose or safely checking unknown values.

Details

A refinement returns a type predicate (a is B). Use it with if or filter to narrow types.

Example (Narrowing unknown values)

import { Predicate } from "effect"

const isString: Predicate.Refinement<unknown, string> = (u): u is string => typeof u === "string"

const data: unknown = "hello"
if (isString(data)) {
  console.log(data.toUpperCase())
}

See

• Predicate
• compose
• isString

Signature

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

Source

Since v2.0.0