text: // @flow
  
  function foo(xs: Array<any>) {
    const zs = [];
    xs
      .map(
        x => [],
      )
      .map(ys =>
        ys
        .map(y => [])
        .reduce((a, b) => [...a, ...b], []),
      )
      .reduce((a, b) => [...a, ...b], [])
      .forEach(z => {
          zs.push(z);
      });
  }
  