A sample script to find words in a string that are of even length and are also palindromes.

example.hs

{-
    Write a function called `evenAndPalindromeStrings` 
    that takes a string as an input and returns the
    words in the string that are of even length and are
    also palindromes.
    Input - "abba cbbc cbc"
    Ouptut - ["abba","cbbc"]

    Psuedo code - 
    1) Break the string by spaces into a list of words
    2) For each word - 
        if it is of even length and is a palindrome
        pick it as an answer
    
    NOTE - A string is just a list of chars
-}

-- function to  calculate length of a list
len :: [a] -> Int
len []  = 0
len (x:xs) = 1 + len xs

-- function to check if a number is even
isEven :: Int -> Bool
isEven num = num `mod` 2 == 0

-- function to split a string by space
splitBySpace :: String -> [String]
splitBySpace "" = [""]
splitBySpace (x:xs)
    | x == ' ' = "" : remaining
    | otherwise =  (x : head remaining) : tail remaining
    where
        remaining = splitBySpace xs

-- reverses a given word
reverseString :: String -> String
reverseString "" = ""
reverseString (x : xs) = reverseString xs ++ [x]

-- function to check if a word is palindrome
isPalindrome :: String -> Bool
isPalindrome "" = True
isPalindrome word = word ==  (reverseString word)

evenAndPalindromeStrings :: String -> [String]
evenAndPalindromeStrings "" = []
evenAndPalindromeStrings string =
    [word | word <- wordsInStrings, isPalindrome word, isWordOfEvenLength word]
    where 
        wordsInStrings = splitBySpace string
        isWordOfEvenLength word = isEven (len word)