Wraps a plain function as a Lambda value so it can be used with map, mapPick, and mapOmit.

When to use

Use to create a typed lambda for struct mapping APIs that need type-level input and output tracking.

Details

The type parameter L encodes both the input and output types at the type level, allowing the compiler to track how struct value types change. At runtime, the returned value is the same function; lambda only adjusts the type.

Example (Wrapping values in arrays)

import { pipe, Struct } from "effect"

interface AsArray extends Struct.Lambda {
  <A>(self: A): Array<A>
  readonly "~lambda.out": Array<this["~lambda.in"]>
}

const asArray = Struct.lambda<AsArray>((a) => [a])
const result = pipe({ x: 1, y: "hello" }, Struct.map(asArray))
console.log(result) // { x: [1], y: ["hello"] }