How would I use lens in Haskell to duplicate Python's enumerate?

Question

Python\'s enumerate on lists can be written as zip [0..]. I looked at Control.Lens.Traversal and Control.Lens.Indexed, but I couldn\'t figure out how to use len

Answer 1

You're ignoring the Applicative context on itraverse. You need something for it to be working with. But the something can be boring, like Identity.

imap f = runIdentity . itraverse (\i a -> return (f i a))

And then you get what you're looking for:

> imap (,) [1,2,3]
[(0,1),(1,2),(2,3)]