FuncType - v1.8.0
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    Class RepeatExhausted<A>

    Error surfaced by value-driven repeat combinators when the iteration bound is reached without the predicate being satisfied. Carries the last observed value so callers can report what the loop settled on.

    Type parameter A is the value type the loop was producing (or the state type for IO.iterate).

    If the step effect has E = unknown (common when lifting a Promise via IO(() => ...) or IO.async(...) — see the JSDoc on those constructors), TypeScript's union algebra collapses unknown | RepeatExhausted<A> back to unknown, and RepeatExhausted<A> is lost from the surface type. The runtime behavior is still correct (the RepeatExhausted instance is in the Left at runtime — see reporter's JSON in issue #221) — but consumers need a narrowing step to recover it. Use RepeatExhausted.is:

    const res = await IO.iterate(seed, step, done, { max: 20 }).run()
    res.fold(
      (e) => {
        if (RepeatExhausted.is<StepState>(e)) {
          // e is now RepeatExhausted<StepState>; e.lastValue is StepState
          return e.lastValue
        }
        // e is still the collapsed E channel — handle as the caller sees fit
        throw e as Error
      },
      (settled) => settled,
    )

    The alternative — annotating step's error channel so E is a concrete tagged type — also works and preserves RepeatExhausted<A> in the union:

    const step = (s: S): IO<never, never, S> =>
      IO(() => runOnce(s)).mapError((_e) => _e as never)
    // iterate result E channel: never | RepeatExhausted<S> === RepeatExhausted<S>

    Type Parameters

    • A = unknown

    Hierarchy

    • Error
      • RepeatExhausted
    Index
    constructor
    _tag lastValue? max
    is

    • Type Parameters

      • A = unknown

      Parameters

      • max: number
      • OptionallastValue: A
      • Optionalmessage: string

      Returns RepeatExhausted<A>

    Readonly_tag

    _tag: "RepeatExhausted" = ...
    lastValue?: A
    max: number

    • Runtime type guard. Narrows an unknown (or wider) value to RepeatExhausted<A> when the tag matches. Use this to recover typed exhaustion when the E channel has collapsed to unknown — a common situation when the step effect is lifted from a Promise via IO(...) or IO.async(...). See the class-level JSDoc for a full example.

      The type parameter A is an unchecked assertion — the guard confirms the shape is a RepeatExhausted, but cannot verify lastValue matches A at runtime. Callers pass the state/value type they expect the loop to have been producing.

      Type Parameters

      • A = unknown

      Parameters

      • e: unknown

      Returns e is RepeatExhausted<A>

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