stringOfInteger :: Integer -> String
stringOfInteger 0 = "0"
stringOfInteger 1 = "1"
stringOfInteger 2 = "2"
stringOfInteger 3 = "3"
stringOfInteger 4 = "4"
stringOfInteger 5 = "5"
stringOfInteger 6 = "6"
stringOfInteger 7 = "7"
stringOfInteger 8 = "8"
stringOfInteger 9 = "9"
stringOfInteger
 | x <= 0 = "-" ++ deComp x
 | x > 9 = deComp x
     where
         deComp x = stringOfInteger (x `div` 10) ++ stringOfInteger (x `mod` 10)