import Control.Applicative
import Control.Monad
import Data.Char
import Data.List
import System.IO
num2wstr :: Integer -> Maybe [String]
num2wstr 0 = Just []
num2wstr n | n < 0 = (:) <$> Just "minus" <*> (num2wstr $ abs n)
num2wstr n | n < 100 = let
concat = (++) <$> tens <*> ("" : map ('-' :) simple)
simple = ["one", "two", "three", "four", "five", "six", "seven", "eight", "nine"]
simplex = ["ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"]
tens = ["twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"]
in Just [(simple ++ simplex ++ concat) !! (fromIntegral $ n - 1)]
num2wstr n = foldM dot [] $ transpose [numbers, tail numbers]
where
dot' n xn xs = (\x y -> x ++ [xs] ++ y)
<$> num2wstr (n `div` xn)
<*> num2wstr (n `mod` xn)
dot a@(_:_) _ = Just a
dot a ([(xn,xs),(yn,_)])
| n < xn * yn `div` xn = dot' n xn xs
| otherwise = Just a
dot a ([(xn,xs)])
| n < xn * xn = dot' n xn xs
| otherwise = Nothing
numbers = [
(10 ^ 2, "hundred"),
(10 ^ 3, "thousand"),
(10 ^ 6, "million"),
(10 ^ 9, "billion"),
(10 ^ 12, "trillion"),
(10 ^ 15, "quadrillion"),
(10 ^ 18, "quintillion"),
(10 ^ 21, "sextillion"),
(10 ^ 24, "septillion"),
(10 ^ 27, "octillion"),
(10 ^ 30, "nonillion"),
(10 ^ 33, "decillion"),
(10 ^ 36, "undecillion"),
(10 ^ 39, "duodecillion"),
(10 ^ 42, "tredecillion"),
(10 ^ 45, "quattuordecillion"),
(10 ^ 48, "quindecillion"),
(10 ^ 51, "sexdecillion"),
(10 ^ 54, "septendecillion"),
(10 ^ 57, "octodecillion"),
(10 ^ 60, "novemdecillion"),
(10 ^ 63, "vigintillion"),
(10 ^ 66, "unvigintillion"),
(10 ^ 69, "duovigintillion"),
(10 ^ 72, "tresvigintillion"),
(10 ^ 75, "quattuorvigintillion"),
(10 ^ 78, "quinquavigintillion"),
(10 ^ 81, "sesvigintillion"),
(10 ^ 84, "septemvigintillion"),
(10 ^ 87, "octovigintillion"),
(10 ^ 90, "novemvigintillion"),
(10 ^ 93, "trigintillion"),
(10 ^ 96, "untrigintillion"),
(10 ^ 99, "duotrigintillion"),
(10 ^ 102, "trestrigintillion"),
(10 ^ 105, "quattuortrigintillion"),
(10 ^ 108, "quinquatrigintillion"),
(10 ^ 111, "sestrigintillion"),
(10 ^ 114, "septentrigitillion"),
(10 ^ 117, "octotrigintillion"),
(10 ^ 120, "noventrigintillion"),
(10 ^ 123, "quadragintillion"),
(10 ^ 153, "quinquagintillion"),
(10 ^ 183, "sexagintillion"),
(10 ^ 213, "septuagintillion"),
(10 ^ 243, "octogintillion"),
(10 ^ 273, "nonagintillion"),
(10 ^ 303, "centillion"),
(10 ^ 306, "uncentillion"),
(10 ^ 309, "duocentillion"),
(10 ^ 312, "trescentillion"),
(10 ^ 333, "decicentillion"),
(10 ^ 336, "undecicentillion"),
(10 ^ 363, "viginticentillion"),
(10 ^ 366, "unviginticentillion"),
(10 ^ 393, "trigintacentillion"),
(10 ^ 423, "quadragintacentillion"),
(10 ^ 453, "quinquagintacentillion"),
(10 ^ 483, "sexagintacentillion"),
(10 ^ 513, "septuagintacentillion"),
(10 ^ 543, "octogintacentillion"),
(10 ^ 573, "nonagintacentillion"),
(10 ^ 603, "ducentillion"),
(10 ^ 903, "trecentillion"),
(10 ^ 1203, "quadringentillion"),
(10 ^ 1503, "quingentillion"),
(10 ^ 1803, "sescentillion"),
(10 ^ 2103, "septingentillion"),
(10 ^ 2403, "octingentillion"),
(10 ^ 2703, "nongentillion")]
num2wstr' :: Integer -> String
num2wstr' 0 = "Zero."
num2wstr' x =
case num2wstr x of
Just xs -> toUpper' . (++ ".") . intercalate " " $ xs
Nothing -> "Number too large."
where
toUpper' (x:xs) = toUpper x : xs
main :: IO()
main = forever $ do
putStr "> "
hFlush stdout
x <- getLine
case reads x :: [(Integer, String)] of
[(x, y)] | null $ y \\ " " -> putStrLn $ num2wstr' x
otherwise -> putStrLn "Not a valid number."