Deriving a Read instance from a Parsec parser

gistfile1.hs

import Text.Parsec hiding ((<|>), many)
import Text.Parsec.String
import Text.Printf
import Control.Applicative

data MyType = Single Int
            | Tuple MyType MyType

instance Show MyType where
      show (Single x) = show x
      show (Tuple x y) = printf "(%s %s)" (show x) (show y)

-- > print $ Tuple (Tuple (Single 1) (Single 2)) (Single 3)
-- >>> ((1 2) 3)

tupleP :: Parser MyType
tupleP = between (char '(') (char ')') $
      Tuple <$> myTypeP <* space <*> myTypeP

-- Don't worry about read failing, in production code there's
-- better ways of doing this of course. Here it's just a hack
-- to make this code shorter.
singleP :: Parser MyType
singleP = Single . read <$> many1 digit

myTypeP :: Parser MyType
myTypeP = tupleP <|> singleP

-- > parse tupleP "" "((1 2) 3)"
-- >>> Right ((1 2) 3)

instance Read MyType where
      readsPrec = undefined -- ?