Error Accumulation

Combinators such as Effect.all and Effect.forEach fail fast by default. Validation often needs different behavior: evaluate every input and report all problems together.

validate

Effect.validate applies an effectful function to every element. If all elements succeed, it returns all success values. If any fail, it returns every error as a non-empty array and discards the successes.

Example (Collecting Validation Errors)

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import { Effect, Exit } from "effect"
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const program = Effect.validate([1, 2, 3, 4], (value) =>
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  value % 2 === 0 ? Effect.succeed(value) : Effect.fail(`${value} is not even`),
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)
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Effect.runSyncExit(program) // => Exit.fail(["1 is not even", "3 is not even"])

Every element is evaluated. Use { concurrency } to control parallelism and { discard: true } when only validation, not the success values, is needed.

partition

Effect.partition also evaluates every element, but never fails. It returns [failures, successes], preserving both sides.

Example (Partitioning Failures and Successes)

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import { Effect } from "effect"
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const program = Effect.partition([0, 1, 2, 3, 4], (value) =>
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  value % 2 === 0 ? Effect.succeed(value) : Effect.fail(`${value} is not even`),
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)
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Effect.runSync(program) // => [["1 is not even", "3 is not even"], [0, 2, 4]]

Like validate, partition accepts a concurrency option.