Re: Using an accumulator, "iterating"...

Brett Kelly wrote:

I'm trying to write a function that takes a list and a element (same type) and returns the index of the first instance of the element in the list. like: getindex "brett" 'e' would return 2, etc.

i'm trying to accomplish this using an accumulator, here's what i've got:

pyindex :: Eq a => a -> [a] -> Maybe Int pyindex c l = pyindex' 0 chr (x:xs)

None of chr, x or xs are defined here; if you change the above line to: pyindex c l = pyindex' 0 c l it works. Except that you will get a match failure if the list doesn't contain the specified element, so you also need a base case: pyindex' _ _ [] = Nothing -- Glynn Clements <glynn.clements@virgin.net>