Alternate

[gustaphe]

Adds "Alternate", an iterator that cycles through a number of iterators until one of them runs out.

julia> println(alternate(1:5,"the",-(1:5)));
1
t
-1
2
h
-2
3
e
-3
4

[pepijndevos]

This is not type stable, so will most likely perform poorly. I'd probably do something like

function iterate(it::Interleave, state=(true, iterate(it.a), iterate(it.b)))
    if nothing nonsense
    if state[1]
        state[2][1], (false, iterate(state[2][2], state[3])
    else
        state[3][1], (true, state[2], iterate(state[3][2])
    end
end

[oxinabox]

I would like to call this interleave to match interleaveby which we added yesterday. And the microkanren paper

[gustaphe]

Sounds good to me. I don't have a strong sense of how this was implemented either because it's been a while, so make any changes you want :) (let me know if you need me to do something, I might have some time later this week)