effect-io-ai

Package: effect
Module: Effect

Effect.when

Runs an effect conditionally based on the result of an effectful boolean condition.

When to use

Use when you need an effectful check to decide whether another effect should run while representing the skipped case explicitly.

Details

The condition effect is evaluated first. If it succeeds with true, the source effect is run and its success value is wrapped in Option.some. If it succeeds with false, the source effect is skipped and the result is Option.none. If the condition effect fails, that failure is preserved.

Example (Conditionally running an effect)

import { Console, Effect } from "effect"

const shouldLog = true

const program = Effect.when(
  Console.log("Condition is true!"),
  Effect.succeed(shouldLog)
)

Effect.runPromise(program).then(console.log)
// Output: "Condition is true!"
// { _id: 'Option', _tag: 'Some', value: undefined }

Signature

declare const when: { <E2 = never, R2 = never>(condition: Effect<boolean, E2, R2>): <A, E, R>(self: Effect<A, E, R>) => Effect<Option<A>, E | E2, R | R2>; <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>; }

Source

Since v2.0.0