Foldl traverses with State, foldr traverses with anything

Links
17

I’m going to admit this is going to take me a few reads to understand haha.

I had a no idea lookup in base was written that way. Why is it this way with foldr CPS and not the ez-pz:

0 !? (x:_) = Just x
_ !? [] = Nothing
n !? (_:xs) = (n-1) !? xs
1 Like