Joint Iteration

for Stage 1

Michael Ficarra • September 2023

motivation

• have 2+ iterators that are positionally aligned
• want to process corresponding values together

current state-of-the-art: write your own helper 🙁

function* zip<A, B>(as: Iterable<A>, bs: Iterable<B>): Iterable<[A, B]> {

const iterA = as[Symbol.iterator]();

const iterB = bs[Symbol.iterator]();

​

while (true) {

const iterResultA = iterA.next();

const iterResultB = iterB.next();

​

if (iterResultA.done !== iterResultB.done) {

throw new Error('iterators ended at different times');

}

​

if (iterResultA.done) {

break;

}

​

yield [iterResultA.value, iterResultB.value];

}

}

​

likely shape: static method(s) on Iterator

Iterator.zip(as, bs);

or

Iterator.zip(as, bs, cs, ...);

​

design space: does zipWith obviate zip?

Iterator.zipWith(Math.max, as, bs, cs, ...);

// Math.max(a₀, b₀, c₀), Math.max(a₁, b₁, c₁), ...

​

Iterator.zipWith(Array.of, as, bs, cs, ...);

// [a₀, b₀, c₀], [a₁, b₁, c₁], ...

​

design space: varargs? just 2? Iterable<Iterator>?

Iterator.zip(as, bs);

or

Iterator.zip(as, bs, cs, ...);

or

Iterator.zip([as, bs, cs, ...]);

​

• varargs eliminates the possibility of an options bag for other configurability

​

design space: positional or named iterators?

Iterator.zip({ a: as, b: bs, c: cs });

​

// { a: a₀, b: b₀, c: c₀ },

// { a: a₁, b: b₁, c: c₁ },

// ...

​

​

​

design space: longest / filled / strict

Iterator.zipLongest(as, bs); // fill with undefined

Iterator.zipFilled(as, bs, filler); // fill with filler

Iterator.zipFilled(as, bs, asFiller, bsFiller);

Iterator.zipStrict(as, bs); // throw

prior art: other languages

prior art: JS libraries

Champion's Thoughts

Stage 1?