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

One solution would be to use the State monad with traverse, since it is also Applicative:

enumerate :: (Integral n, Traversable t) => t a -> t (n, a)
enumerate t = evalState (traverse go t) 0
    where
        go a = do
            i <- get
            modify (+1)
            return (i, a)