Remove elements by index in haskell

Question

I'm new in haskell and I'm looking for some standard functions to work with lists by indexes.

My exact problem is that i want to remove 3 elements after every 5. If its not clear enough here is illustration:

OOOOOXXXOOOOOXXX...

I know how to write huge function with many parameters, but is there any clever way to do this?

Answer 1

Here is my take:

deleteAt idx xs = lft ++ rgt
  where (lft, (_:rgt)) = splitAt idx xs

Answer 2

You can count your elements easily:

strip' (x:xs) n | n == 7 = strip' xs 0
                | n >= 5 = strip' xs (n+1)
                | n < 5 = x : strip' xs (n+1)
strip l = strip' l 0

Though open-coding looks shorter:

strip (a:b:c:d:e:_:_:_:xs) = a:b:c:d:e:strip xs
strip (a:b:c:d:e:xs) = a:b:c:d:e:[]
strip xs = xs