effect-io-ai

Package: effect
Module: Array

Array.matchLeft

Pattern-matches on an array from the left, providing the first element and the remaining elements separately.

When to use

Use when you need to branch on an array and handle the non-empty case as the first element plus the remaining elements.

Details

onNonEmpty receives (head, tail) where tail is the rest of the array.

Example (Destructuring head and tail)

import { Array } from "effect"

const matchLeft = Array.matchLeft({
  onEmpty: () => "empty",
  onNonEmpty: (head, tail) => `head: ${head}, tail: ${tail.length}`
})
console.log(matchLeft([])) // "empty"
console.log(matchLeft([1, 2, 3])) // "head: 1, tail: 2"

See

• match — receives the full non-empty array
• matchRight — destructures into init + last

Signature

declare const matchLeft: { <B, A, C = B>(options: { readonly onEmpty: LazyArg<B>; readonly onNonEmpty: (head: A, tail: Array<A>) => C; }): (self: ReadonlyArray<A>) => B | C; <A, B, C = B>(self: ReadonlyArray<A>, options: { readonly onEmpty: LazyArg<B>; readonly onNonEmpty: (head: A, tail: Array<A>) => C; }): B | C; }

Source

Since v2.0.0