It's not just an idiom...

In this program I've taken a list of values and fed it to

zip [1..]

You'll recall that zip takes two lists and returns a new list as long as the shortest of the lists handed to it. Each element of the new list is a pair of values at corresponding positions in the lists, so that, for example,

zip [1..] "hiya" == [(1, 'h'), (2, 'i'), (3, 'y'), (4, 'a')]

Remind you of anything you learned to do as a kid? Yes, it's constructing an bijection from a set (here represented as a list) to the first however many counting numbers, aka counting. Little did I know back then that I was preparing for Haskell.