Number to String (PT)

-- for portuguese language
num2ext :: Int -> String
num2ext n | n >= 100 || n < 0 = ""
          | n < 20 && n >= 10 = case n of
                                  10 -> "dez"
                                  11 -> "onze"
                                  12 -> "doze"
                                  13 -> "treze"
                                  14 -> "catorze"
                                  15 -> "quinze"
                                  16 -> "dezasseis"
                                  17 -> "dezassete"
                                  18 -> "dezoito"
                                  19 -> "dezanove"
          | n < 10            = f (n, snd)
          | n `mod` 10 == 0   = f (n `div` 10, fst)
          | otherwise         = connect . map f $ zip (digits n) [fst, snd]
    where
        f (c,level) | c == 0 = level ("", "zero")
                    | c == 1 = level ("", "um")
                    | c == 2 = level ("vinte", "dois")
                    | c == 3 = level ("trinta", "três")
                    | c == 4 = level ("quarenta", "quatro")
                    | c == 5 = level ("cinquenta", "cinco")
                    | c == 6 = level ("sessenta", "seis")
                    | c == 7 = level ("setenta", "sete")
                    | c == 8 = level ("oitenta", "oito")
                    | c == 9 = level ("noventa", "nove")

        connect (x:[]) = x
        connect (x:y:_) = x ++ " e " ++ y

        digits n | n >= 10   = (n `div` 10) : digits (n `mod` 10)
                 | otherwise = [n]

main = let l = [0..99]
       in mapM_ putStrLn . map show $ zip l (map num2ext l)