Concurrency.pool.worker: def of bend-kit-concurrency@0.2.0.0
Import: import bend-kit-concurrency@0.2.0.0/concurrency.bend as Concurrency
Lines 150-177 of bend-kit-concurrency@0.2.0.0/concurrency.bend: https://jend.leeeet.dev/read.txt?path=bend-kit-concurrency@0.2.0.0/concurrency.bend&start_line=150&end_line=177

import Base

# Takes jobs until the queue is closed and empty, then answers its state.
# Each job takes three steps, so 3 * (jobs + 1) fuel is enough.
def pool.worker(
  ~S: Type, ~A: Type, ~B: Type, ~work: S -> A -> IO(S & B), fuel: Nat,
  +q: Chan(A & Chan(B)), w: Worker<S, A, B>
) -> IO(S):
  match fuel:
    case 0n:
      IO.die(S, 1, "Conc.pool: a worker ran out of fuel")
    case 1n+p:
      match w:
        case WIdle{s}:
          do IO<S>:
            got : Maybe<&1, A & Chan(B)> <- Chan.recv(A & Chan(B), q)
            pool.worker(~S, ~A, ~B, ~work, p, q, WGot{s, got})
        case WGot{s, got}:
          match got:
            case None{}:
              IO.pure(S, s)
            case Some{(a, reply)}:
              do IO<S>:
                sb : S & B <- work(s, a)
                pool.worker(~S, ~A, ~B, ~work, p, q, WDone{sb, reply})
        case WDone{sb, reply}:
          (s, b) = sb
          do IO<S>:
            sent : Result<&1, &1, B, Unit> <- Chan.send(B, reply, b)
            pool.worker(~S, ~A, ~B, ~work, p, q, WIdle{s})

Uses (14):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Chan
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Chan.recv
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Chan.send
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO.bind
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO.die
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=IO.pure
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Pair
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Result
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Sigma
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Unit
  https://jend.leeeet.dev/definition.txt?path=bend-kit-concurrency@0.2.0.0/concurrency.bend&name=Worker