effect-facet-match-core

name: effect-facet-match-core description: Guidance for facet effect/Match#core focused on APIs like is, any, and not. Load after effect-skill-router when this facet is the primary owner.

Effect Facet Match#core

Owned scope

• Owns only effect/Match#core.
• Parent module: effect/Match.

What it is for

• matcher model and constructors. The effect/match module provides a type-safe pattern matching system for TypeScript. Inspired by functional programming, it simplifies conditional logic by replacing verbose if/else or switch statements with a structured and expressive API.

API quick reference

• is
• any
• not
• Not
• tag
• Case
• date
• null
• Only
• tags
• Tags
• type
• when
• When
• Types
• value
• bigint
• number
• Full API list: references/api-reference.md

How to use it

• Keep work focused on the core concern for effect/Match.
• Use the reference docs to select the smallest API surface that solves your task.
• Validate behavior against existing tests before introducing new usage patterns.

Starter example

import { Match } from "effect";

// Simulated dynamic input that can be a string or a number
const input: string | number = "some input";

//      ┌─── string
//      ▼
const result = Match.value(input).pipe(
  // Match if the value is a number
  Match.when(Match.number, (n) => `number: ${n}`),
  // Match if the value is a string
  Match.when(Match.string, (s) => `string: ${s}`),
  // Ensure all possible cases are covered
  Match.exhaustive,
);

console.log(result);
// Output: "string: some input"

Common pitfalls

• Unsafe APIs bypass checks; prefer safe variants unless you control invariants explicitly.
• Prefer explicit, typed combinators over ad-hoc casting or unchecked assumptions.

Not covered here

• Sibling facets under the same parent are out of scope:
  • effect-facet-match-combinators (effect/Match#combinators)
  • effect-facet-match-discriminators (effect/Match#discriminators)
  • effect-facet-match-predicates (effect/Match#predicates)
• Parent module ownership belongs to effect-module-match.

Escalate to

• effect-module-match for parent module-wide workflows.
• effect-skill-router for cross-module routing and ownership checks.

Reference anchors

• Parent tests: packages/effect/test/Match.test.ts
• API details: references/api-reference.md
• Usage notes: references/usage-reference.md
• Ownership mapping: references/owner.md