{-# LANGUAGE NoImplicitPrelude #-}

module Data.Digit.Class.D2(
  D2(..)
, parse2
) where

import Control.Category (id)
import Control.Lens (Prism', (#))

import Data.Functor ((<$))

import Text.Parser.Char(CharParsing, char)
import Text.Parser.Combinators((<?>))

-- $setup
-- >>> import Data.Digit.Class
-- >>> import Text.Parsec(parse, ParseError, eof)
-- >>> import Data.Void(Void)

class D2 d where
  d2 ::
    Prism'
      d
      ()
  x2 ::
    d
  x2 =
    forall d. D2 d => Prism' d ()
d2 forall t b. AReview t b -> b -> t
# ()

instance D2 () where
  d2 :: Prism' () ()
d2 =
    forall {k} (cat :: k -> k -> *) (a :: k). Category cat => cat a a
id
    
-- |
--
-- >>> parse (parse2 <* eof) "test" "2" :: Either ParseError DecDigit
-- Right DecDigit2
--
-- >>> parse parse2 "test" "2xyz" :: Either ParseError DecDigit
-- Right DecDigit2
--
-- >>> isn't _Right (parse parse2 "test" "xyz" :: Either ParseError DecDigit)
-- True
parse2 ::
  (D2 d, CharParsing p) =>
  p d
parse2 :: forall d (p :: * -> *). (D2 d, CharParsing p) => p d
parse2 =
  forall d. D2 d => d
x2 forall (f :: * -> *) a b. Functor f => a -> f b -> f a
<$ forall (m :: * -> *). CharParsing m => Char -> m Char
char Char
'2' forall (m :: * -> *) a. Parsing m => m a -> String -> m a
<?> String
"2"