feat(haskell): add title case

haskell/9_title_case.hs

@@ -0,0 +1,26 @@
+module TitleCase (titleCase) where
+
+import qualified Data.Char as Char
+
+titleCase :: String -> String -> String
+titleCase minor title =
+  unwords $
+    map toTitle (take 1 titleWords)
+    <> map maybeToTitle (drop 1 titleWords)
+  where
+    titleWords, minorWords :: [String]
+    titleWords = words . toLower $ title
+    minorWords = words . toLower $ minor
+
+    maybeToTitle :: String -> String
+    maybeToTitle word
+      | word `elem` minorWords = word
+      | otherwise              = toTitle word
+
+toTitle :: String -> String
+toTitle t = case t of
+  ""     -> ""
+  (x:xs) -> Char.toUpper x : xs
+
+toLower :: String -> String
+toLower = map Char.toLower