On Saturday, 2003-06-21, 03:23, CEST, Brett Kelly wrote:
Hello all,
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) where pyindex' count chr (x:xs) = do if x == chr then return count else pyindex' (count + 1) chr xs
now, i know i've got a syntax problem, because i'm pretty sure my logic is correct (or at least MOSTLY correct).
can anybody see what's wrong with my stuff?
thanks!
Hello, I think, the following code, which uses certain prelude functions, would be clearer and more elegant: pyindex :: Eq a => a -> [a] -> Maybe Int pyindex c l = lookup c (zip l [0 ..]) I would it generally consider better style to not do recursion explicitely but use the recursion already provided by predefined functions like lookup. Wolfgang