Concurrency.select.relay: def of bend-kit-concurrency@0.2.0.0
Import: import bend-kit-concurrency@0.2.0.0/concurrency.bend as Concurrency
Lines 249-277 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=249&end_line=277

import Base

# Forwards each value of src to out as (i, value), then reports on done.
# It stops when src closes, or when out is closed under it.
def select.relay(
  -A: Type, fuel: Nat, +i: U32, +src: Chan(A), +out: Chan(U32 & A),
  +done: Chan(Unit), r: Relay<A>
) -> IO(Result<&1, &1, Unit, Unit>):
  match fuel:
    case 0n:
      Chan.send(Unit, done, Unit{})
    case 1n+p:
      match r:
        case RWait{}:
          do IO<Result<&1, &1, Unit, Unit>>:
            got : Maybe<&1, A> <- Chan.recv(A, src)
            select.relay(A, p, i, src, out, done, RGot{got})
        case RGot{got}:
          match got:
            case None{}:
              Chan.send(Unit, done, Unit{})
            case Some{x}:
              do IO<Result<&1, &1, Unit, Unit>>:
                ok : Result<&1, &1, U32 & A, Unit> <- Chan.send(U32 & A, out, (i, x))
                select.relay(A, p, i, src, out, done, RSent{ok})
        case RSent{ok}:
          match ok:
            case Done{u}:
              select.relay(A, p, i, src, out, done, RWait{})
            case Fail{held}:
              Chan.send(Unit, done, Unit{})

Uses (13):
  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=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=U32
  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=Relay