{-# LANGUAGE NoImplicitPrelude #-} module Data.Digit.Dc( Dc(..) , parsec ) where import Data.Digit.Digit(Digit(Digitc)) import Papa import Text.Parser.Char(CharParsing, char) import Text.Parser.Combinators(()) -- $setup -- >>> import Text.Parsec(parse, ParseError, eof) -- >>> import Data.Void(Void) class Dc d where dc :: Prism' d () xc :: d xc = dc # () instance Dc () where dc = id -- | -- -- >>> parse (parsec <* eof) "test" "c" :: Either ParseError Digit -- Right c -- -- >>> parse parsec "test" "cxyz" :: Either ParseError Digit -- Right c -- -- >>> isn't _Right (parse parsec "test" "xyz" :: Either ParseError Digit) -- True -- -- prop> \c -> c /= 'c' ==> isn't _Right (parse parsec "test" [c] :: Either ParseError Digit) parsec :: (Dc d, CharParsing p) => p d parsec = xc <$ char 'c' "c" instance Dc Digit where dc = prism' (\() -> Digitc) (\d -> case d of Digitc -> Just () _ -> Nothing)