effect-io-ai

Package: effect
Module: Data

Data.TaggedEnum.Constructor

The full constructors-and-matchers object type returned by taggedEnum.

When to use

Use when you want to annotate an exported constructor bundle so downstream code keeps exact variant constructors and exhaustive matching.

Details

Includes:

• A constructor function for each variant (keyed by tag name)
• $is(tag) — returns a type-guard that checks only the _tag field; safe when the tag is globally unique and the value was produced by your constructors. For untrusted input, validate with the Schema module first.
• $match — exhaustive pattern matching (data-last or data-first)

Example (Using the constructor object)

import { Data } from "effect"

type Shape =
  | { readonly _tag: "Circle"; readonly radius: number }
  | { readonly _tag: "Rect"; readonly w: number; readonly h: number }

const { Circle, Rect, $is, $match } = Data.taggedEnum<Shape>()

const shape = Circle({ radius: 10 })

// Type guard
if ($is("Circle")(shape)) {
  console.log(shape.radius)
}

// Pattern matching
const label = $match(shape, {
  Circle: (s) => `circle r=${s.radius}`,
  Rect: (s) => `rect ${s.w}x${s.h}`
})

See

• taggedEnum — creates constructors and matchers

Signature

type Constructor<A> = Types.Simplify<
    {
      readonly [Tag in A["_tag"]]: ConstructorFrom<
        Extract<A, { readonly _tag: Tag }>,
        "_tag"
      >
    } & {
      readonly $is: <Tag extends A["_tag"]>(
        tag: Tag
      ) => (u: unknown) => u is Extract<A, { readonly _tag: Tag }>
      readonly $match: {
        <
          Cases extends {
            readonly [Tag in A["_tag"]]: (
              args: Extract<A, { readonly _tag: Tag }>
            ) => any
          }
        >(
          cases: Cases
        ): (value: A) => Unify<ReturnType<Cases[A["_tag"]]>>
        <
          Cases extends {
            readonly [Tag in A["_tag"]]: (
              args: Extract<A, { readonly _tag: Tag }>
            ) => any
          }
        >(
          value: A,
          cases: Cases
        ): Unify<ReturnType<Cases[A["_tag"]]>>
      }
    }
  >

Source

Since v3.1.0