Artie Gold 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) 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.
Maybe *is* a monad:
instance Monad Maybe where
Just x >>= k = k x
Nothing >>= k = Nothing
return = Just
fail s = Nothing
Having said that, treating it as such doesn't really have any benefit
here.
--
Glynn Clements