Hi all, This is my first post in this forum, I'm pretty new to Haskell (although I have some previous experience in functional programming with OCaml). I'm trying to write the typical function that determines if a list is a palindrome. The typical answer would be something like: isPalindrome xs = xs == (reverse xs) But I find this pretty inefficient (duplication of the list and double of needed comparisons). So I tried my own version using just indexes: isPalindrome xs = isPalindrome' 0 (length xs) where isPalindrome' i j = if i == j -- line 43 then True else if (xs !! i) == (xs !! (j-1)) then isPalindrome' (i+1) (j-1) else False But, when trying to load this in ghci it throws the following error: xxx.hs:43:12: parse error (possibly incorrect indentation) Failed, modules loaded: none. (Line 43 is marked in the code) I seems that the definition of isPalindrome' must be in one line. So, this works as expected: isPalindrome xs = isPalindrome' 0 (length xs) where isPalindrome' i j = if i == j then True else if (xs !! i) == (xs !! (j-1)) then isPalindrome' (i+1) (j-1) else False Is there any way to make the local definition of isPalindrome' more readable? Any help in understanding this would be appreciated Thanks in advance, M;