import Text.ParserCombinators.Parsec


data Region = UnitCircle | Scale Int Region | Union Region Region
                deriving Show

parseTwoArgs c x y =
  do
    char '('
    a <- x
    char ','
    b <- y
    char ')'
    return (c a b)


parseRegion :: Parser Region
parseRegion = do (try parseUnitCircle) <|> parseScale <|> parseUnion

parseUnitCircle :: Parser Region
parseUnitCircle =
   do
     string "unitcircle"
     return UnitCircle

parseScale = parseTwoArgs Scale number parseRegion

parseUnion = parseTwoArgs Union parseRegion parseRegion

number  :: Parser Int
number  = do{ ds <- many1 digit
            ; return (read ds)
            }
        <?> "number"