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?
Sure. Three comments: 1) You don't need (or want) the `do' -- that's used for dealing with monads. 2) The function's signature indicates a return type of `Maybe Int', yet you're trying to return an Int. 3) What if you _don't_ find the target? Additional comments: The `if...then...else' form may not be the clearest way -- or the most `Haskell-ish' way of expressing this computation. You may want to look through the standard prelude to find how things like this are usually done. Good luck and HTH, --ag -- Artie Gold -- Austin, Texas