@thi.ng/transducers-async/source.js

Async versions of various highly composable transducers, reducers and iterators

import { fifo } from "@thi.ng/buffers/fifo";
import { isNumber } from "@thi.ng/checks/is-number";
import { illegalState } from "@thi.ng/errors/illegal-state";
const source = (initial, buffer = 1) => {
  const queue = isNumber(buffer) ? fifo(buffer) : buffer;
  let last = initial;
  let state = 0;
  let promise;
  let resolve;
  const newPromise = () => {
    promise = new Promise(($resolve) => {
      resolve = $resolve;
    });
  };
  newPromise();
  const gen = async function* () {
    while (true) {
      const val = await promise;
      last = val;
      if (val === void 0) break;
      yield val;
      newPromise();
      if (queue.readable()) resolve(queue.read());
    }
    state = 2;
  }();
  gen.write = (x) => {
    if (state > 0) return;
    if (resolve) {
      resolve(x);
      resolve = void 0;
    } else if (queue.writable()) {
      queue.write(x);
      if (x === void 0) state = 1;
    } else illegalState("buffer overflow");
  };
  gen.update = (fn, ...args) => gen.write(fn(last, ...args));
  gen.close = () => gen.write(void 0);
  gen.deref = () => last;
  if (initial !== void 0) gen.write(initial);
  return gen;
};
export {
  source
};