const outputs = await pipe(
    postIds,// array of numbers, which is... already an iterable
    mapGen(fetchById),// generator of an array of eventually all resolved promises (requested in chunks of 3)
    chunkGen(5),// generator of arrays of 5 promises, our "batch"
    spreadBatchesAsyncGen,// async generator of individual resolved promises
    forEachAsyncGen(renderPost)// Promise of an array of numbers
)