Hacker News Reader

Comment by kazinator | Hacker News Reader

Haskell needs "zip3" when there are three arguments to zip.

That's a design pattern for optional arguments straight out of ISO C.

I think it would be possible to create a generalised `zipN` function, using the Haskell printf trick[0], but it would be a lot of complication for little benefit. It's rare that you need to merge that many streams at once, and adding a single digit is not a huge hassle in those cases. Also I'd probably consider splitting the operation up into stages if I was using anything higher than `zipWith3`.

[0]http://stackoverflow.com/questions/7828072/how-does-haskell-...

You also have an equivalent on a family of isomorphic types, namely the types

    forall z. (a -> b -> c -> ... -> z) -> ZipList z

This is gotten by taking your `list_a :: [a]` etc. and writing:

    \f -> f <$> ZipList list_a <*> ZipList list_b <*> ZipList list_c <*> ...

You can of course also use Haskell pair-stacks to do all of this, storing (a, b, c, ...) as the type (a, (b, (c, ... ())))...

Reply on news.ycombinator.com