Error Accumulation

Independent checks often need to report every problem in one response. Use validation to collect domain errors, or partitioning when successful results are useful even if other inputs fail.

Upstream page

Validating every computation

error InvalidHandle {
  input: string
}

function validateHandle(input: string) {
  const handle = input.trim()
  if (handle.length < 3) throw new InvalidHandle({ input })
  return handle.toLowerCase()
}

function validateTeam() {
  return Effect.validate(
    ["Jo", "RIVER", ""],
    (input) => validateHandle(input),
    { concurrency: 2 }
  )
}
// string[]![InvalidHandle, ...InvalidHandle[]]!

Effect.validate runs each input's computation even when others fail with typed errors. If any fail, the error channel contains a nonempty array of every domain error and the successful values are discarded. If all succeed, it returns an array of successes.

function checkTeamOnly() {
  Effect.validate(["RIVER", "SKY"], (input) => validateHandle(input), {
    discard: true,
    concurrency: 2
  })
}

discard: true returns void on success when you only need validation. Concurrency controls how many independent checks run at once. A cause without an expected failure still terminates the computation. These APIs use Effect's error-to-result conversion, so a mixed cause containing an expected failure can be reduced to that error and lose its other reasons; use cause-level inspection when those reasons matter.

Partitioning successes and failures

function inspectTeam() {
  const [handles, errors] = Effect.partition(
    ["Jo", "RIVER", ""],
    (input) => validateHandle(input),
    { concurrency: 2 }
  )
  return {
    handles,                       // ["river"]
    rejected: errors.length        // 2
  }
}
// { handles: string[]; rejected: number }!!

The tuple order is [successes, failures]. partition preserves both arrays and removes expected errors from E, letting you accept valid inputs while reporting rejected ones. Its mixed-cause policy is the same as validation's.

Coming from Effect

Pass an ordinary Effeck callback to validate or partition. A plain array map cannot run a callback that needs services, pauses, or has a typed failure.