-- | OK, I lied about "Network.DNS.RBL.Domain.Digit" and
-- "Network.DNS.RBL.Domain.Letter" being the simplest modules you'd
-- ever see. Because this is. It contains the 'Hyphen' type and a
-- Parsec parser to parse one. We don't export its constructor because
-- then you could do something dumb like stick a letter inside one.
--
module Network.DNS.RBL.Domain.Hyphen (
  Hyphen,
  hyphen )
where

import Text.Parsec ( char )
import Text.Parsec.String ( Parser )

import Network.DNS.RBL.Pretty ( Pretty(..) )



-- | A type representing a single hyphen character.
--
--   ==== _Examples_
--
--   >>> Hyphen
--   Hyphen
--
--   >>> let h1 = Hyphen
--   >>> let h2 = Hyphen
--   >>> h1 == h2
--   True
--
data Hyphen = Hyphen deriving (Eq, Show)


-- | Pretty-print a hyphen; they all display as \'-\'.
--
--   ==== _Examples_
--
--   >>> let h = Hyphen
--   >>> pretty_print h
--   -
--
instance Pretty Hyphen where pretty_show _ = "-"


-- | Parse a single hyphen and return a 'Hyphen'.
--
--   ==== _Examples_
--
--   >>> import Text.Parsec ( parseTest )
--
--   Hyphens are parsed:
--
--   >>> parseTest hyphen "-"
--   Hyphen
--
--   But not letters or digits:
--
--   >>> parseTest hyphen "1"
--   parse error at (line 1, column 1):
--   unexpected "1"
--   expecting "-"
--
--   >>> parseTest hyphen "x"
--   parse error at (line 1, column 1):
--   unexpected "x"
--   expecting "-"
--
hyphen :: Parser Hyphen
hyphen = char '-' >> return Hyphen