sync-async-adapter.js

let Read = {};
let End = {};

function* lexer() {
  let accumulatedChars = [];
  while (true) {
    let inp = yield Read;
    if (inp === End) {
      if (accumulatedChars.length > 0) yield accumulatedChars.join('');
      return;
    }
    if (inp === '(' || inp === ')') {
      if (accumulatedChars.length > 0) {
        yield accumulatedChars.join('');
        accumulatedChars = [];
      }
      yield inp;
    } else accumulatedChars.push(inp);
  }
}

function* syncAdapter(gen, iterable) {
  let reader = gen();
  let currentVal = reader.next();
  if (currentVal.done) return;
  for (let item of iterable) {
    if (currentVal.value === Read) {
      currentVal = reader.next(item);
    }
    while (currentVal.value !== Read && !currentVal.done) {
      yield currentVal.value;
      currentVal = reader.next();
    }
  }
  currentVal = reader.next(End);
  while (!currentVal.done && currentVal.value !== Read) {
    yield currentVal.value;
    currentVal = reader.next();
  }
}

function* asyncAdapter(gen, iterable) {
  let reader = gen();
  let currentVal = reader.next();
  if (currentVal.done) return;
  for await (let item of iterable) {
    if (currentVal.value === Read) {
      currentVal = reader.next(item);
    }
    while (currentVal.value !== Read && !currentVal.done) {
      yield currentVal.value;
      currentVal = reader.next();
    }
  }
  currentVal = reader.next(End);
  while (!currentVal.done && currentVal.value !== Read) {
    yield currentVal.value;
    currentVal = reader.next();
  }
}


let parseThis = 'a(bcd(ef)gh)ijk'.split('');

let sa = syncAdapter(lexer, parseThis);
for (let production of sa) {
  console.log(production);
}