export const combine: {
  <OutElem2, OutErr2, OutDone2, InElem2, InErr2, InDone2, Env2, S, OutElem, OutErr, OutDone, A, E, R>(
    that: Channel<OutElem2, OutErr2, OutDone2, InElem2, InErr2, InDone2, Env2>,
    s: LazyArg<S>,
    f: (
      s: S,
      pullLeft: Pull.Pull<OutElem, OutErr, OutDone>,
      pullRight: Pull.Pull<OutElem2, OutErr2, OutDone2>
    ) => Effect.Effect<readonly [A, S], E, R>
  ): <InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<
    A,
    Pull.ExcludeDone<E>,
    Cause.Done.Extract<E>,
    InElem & InElem2,
    InErr & InErr2,
    InDone & InDone2,
    Env | Env2 | R
  >
  <
    OutElem,
    OutErr,
    OutDone,
    InElem,
    InErr,
    InDone,
    Env,
    OutElem2,
    OutErr2,
    OutDone2,
    InElem2,
    InErr2,
    InDone2,
    Env2,
    S,
    A,
    E,
    R
  >(
    self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>,
    that: Channel<OutElem2, OutErr2, OutDone2, InElem2, InErr2, InDone2, Env2>,
    s: LazyArg<S>,
    f: (
      s: S,
      pullLeft: Pull.Pull<OutElem, OutErr, OutDone>,
      pullRight: Pull.Pull<OutElem2, OutErr2, OutDone2>
    ) => Effect.Effect<readonly [A, S], E, R>
  ): Channel<
    A,
    Pull.ExcludeDone<E>,
    Cause.Done.Extract<E>,
    InElem & InElem2,
    InErr & InErr2,
    InDone & InDone2,
    Env | Env2 | R
  >
} = dual(4, <
  OutElem,
  OutErr,
  OutDone,
  InElem,
  InErr,
  InDone,
  Env,
  OutElem2,
  OutErr2,
  OutDone2,
  InElem2,
  InErr2,
  InDone2,
  Env2,
  S,
  A,
  E,
  R
>(
  self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>,
  that: Channel<OutElem2, OutErr2, OutDone2, InElem2, InErr2, InDone2, Env2>,
  s: LazyArg<S>,
  f: (
    s: S,
    pullLeft: Pull.Pull<OutElem, OutErr, OutDone>,
    pullRight: Pull.Pull<OutElem2, OutErr2, OutDone2>
  ) => Effect.Effect<readonly [A, S], E, R>
): Channel<
  A,
  Pull.ExcludeDone<E>,
  Cause.Done.Extract<E>,
  InElem & InElem2,
  InErr & InErr2,
  InDone & InDone2,
  Env | Env2 | R
> =>
  fromTransform(Effect.fnUntraced(function*(upstream, scope) {
    const leftPull = yield* toTransform(self)(upstream, scope)
    const rightPull = yield* toTransform(that)(upstream, scope)
    let state = s()
    return Effect.suspend(() => {
      const combinedPull = f(state, leftPull, rightPull)
      return Effect.map(combinedPull, ([a, s1]) => {
        state = s1
        return a
      })
    })
  })))