import Text.ParserCombinators.Parsec


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

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

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

parseScale :: Parser Region
parseScale =
  do
    string "scale"
    char '('
    r1 <- number
    char ','
    r2 <- parseRegion
    return $ Scale r1 r2

parseUnion =
   do
     string "union"
     char '('
     r1 <- parseRegion
     char ','
     r2 <- parseRegion
     return $ Union r1 r2


number  :: Parser String
number  = many1 digit