shift :: Int -> Char -> Char
shift n c | isLower c =  int2let ((let2int c + n) `mod` 26)
          | otherwise = c
shift :: Int -> Char -> Char
shift n c | isLower c =  int2let ((let2int c + n) `mod` 26)
          | otherwise = c
shift n c | isLower c =  int2let ((let2int c + n) `mod` 26)
          | otherwise = c