Chunk

This function returns self, broken up into non-overlapping arrays of length n:

func chunk<T>(_ list: [T], length: Int) -> [[T]] {

    // Simplify the type signature by introducing a `typealias`

    typealias Acc = (stack: [[T]], cur: [T], cnt: Int)

    

    // Start with a `cnt` of 0

    let reducedList = list.reduce((stack: [], cur: [], cnt: 0), { (ac: Acc, o: T) -> Acc in

       if ac.cnt == length {

           return (stack: ac.stack + [ac.cur], cur: [o], cnt: 1)

       } else {

           return (stack: ac.stack, cur: ac.cur + [o], cnt: ac.cnt + 1)

       }

    })

    return reducedList.stack + [reducedList.cur]

}

print(chunk([1, 2, 3, 4, 5, 6, 7], length: 2))

// [[1, 2], [3, 4], [5, 6], [7]]

This function uses a more complicated accumulator consisting out of a stack, the current list, and the count.