Re: [Haskell-cafe] generalized, tail-recursive left fold that can finish tne computation prematurely

Hi.

while playing with folds and trying to implement `!!` by folding, I came to the conclusion that:

- `foldr` is unsuitable because it counts the elements from the end, while `!!` needs counting from the start (and it's not tail recursive).

What is the problem with the following definition using foldr?

index :: Int -> [a] -> a index n xs = foldr (\ x r n -> if n == 0 then x else r (n - 1)) (const (error $ "No such index")) xs n

Cheers, Andres