Parallel and Sequential Errors

Most Effect combinators fail fast: once an effect fails, later work is not started and concurrent work is interrupted. Some operations can nevertheless produce several failure reasons, for example when concurrent fibers fail together or when both an operation and its finalizer fail.

Flat Causes

Cause<E> contains a flat readonly array of Reason<E> values:

type Reason<E> = Cause.Fail<E> | Cause.Die | Cause.Interrupt

Reasons combined sequentially and reasons combined in parallel use the same reasons array representation.

Example (Inspecting Multiple Reasons)

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import { Cause } from "effect"
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const cause = Cause.combine(
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  Cause.fail("request failed"),
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  Cause.die(new Error("finalizer failed")),
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)
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cause.reasons.map((reason) => reason._tag) // => ["Fail", "Die"]

Use Cause.hasFails, Cause.hasDies, and Cause.hasInterrupts when only the kind of failure matters. Use cause.reasons or extractors such as Cause.findError and Cause.findDefect when the individual values are needed.

Accumulating Domain Errors

Multiple typed validation errors are usually better represented as data rather than as multiple Cause reasons. Use Effect.validate to collect every typed error, or Effect.partition to preserve both failures and successes.