Executes an effectful operation for each element in an Iterable.

When to use

Use to traverse an iterable with an effectful function while preserving element order in the collected results.

Details

The forEach function applies a provided operation to each element in the iterable, producing a new effect that returns an array of results.

If any effect fails, the iteration stops immediately (short-circuiting), and the error is propagated.

Concurrency:

The concurrency option controls how many operations are performed concurrently. By default, the operations are performed sequentially.

Discarding Results:

If the discard option is set to true, the intermediate results are not collected, and the final result of the operation is void.

Example (Mapping over an iterable with effects)

import { Console, Effect } from "effect"

const result = Effect.forEach(
  [1, 2, 3, 4, 5],
  (n, index) =>
    Console.log(`Currently at index ${index}`).pipe(Effect.as(n * 2))
)

Effect.runPromise(result).then(console.log)
// Output:
// Currently at index 0
// Currently at index 1
// Currently at index 2
// Currently at index 3
// Currently at index 4
// [ 2, 4, 6, 8, 10 ]

Example (Running effects without collecting results)

import { Console, Effect } from "effect"

// Apply effects but discard the results
const result = Effect.forEach(
  [1, 2, 3, 4, 5],
  (n, index) =>
    Console.log(`Currently at index ${index}`).pipe(Effect.as(n * 2)),
  { discard: true }
)

Effect.runPromise(result).then(console.log)
// Output:
// Currently at index 0
// Currently at index 1
// Currently at index 2
// Currently at index 3
// Currently at index 4
// undefined