harbl/src/Network/DNS/RBL/Domain/Hyphen.hs

   1 -- | OK, I lied about "Network.DNS.RBL.Domain.Digit" and
   2 -- "Network.DNS.RBL.Domain.Letter" being the simplest modules you'd
   3 -- ever see. Because this is. It contains the 'Hyphen' type and a
   4 -- Parsec parser to parse one. We don't export its constructor because
   5 -- then you could do something dumb like stick a letter inside one.
   6 --
   7 module Network.DNS.RBL.Domain.Hyphen (
   8   Hyphen,
   9   hyphen )
  10 where
  11
  12 import Text.Parsec ( char )
  13 import Text.Parsec.String ( Parser )
  14
  15 import Network.DNS.RBL.Pretty ( Pretty(..) )
  16
  17
  18
  19 -- | A type representing a single hyphen character.
  20 --
  21 --   ==== _Examples_
  22 --
  23 --   >>> Hyphen
  24 --   Hyphen
  25 --
  26 --   >>> let h1 = Hyphen
  27 --   >>> let h2 = Hyphen
  28 --   >>> h1 == h2
  29 --   True
  30 --
  31 data Hyphen = Hyphen deriving (Eq, Show)
  32
  33
  34 -- | Pretty-print a hyphen; they all display as \'-\'.
  35 --
  36 --   ==== _Examples_
  37 --
  38 --   >>> let h = Hyphen
  39 --   >>> pretty_print h
  40 --   -
  41 --
  42 instance Pretty Hyphen where pretty_show _ = "-"
  43
  44
  45 -- | Parse a single hyphen and return a 'Hyphen'.
  46 --
  47 --   ==== _Examples_
  48 --
  49 --   >>> import Text.Parsec ( parseTest )
  50 --
  51 --   Hyphens are parsed:
  52 --
  53 --   >>> parseTest hyphen "-"
  54 --   Hyphen
  55 --
  56 --   But not letters or digits:
  57 --
  58 --   >>> parseTest hyphen "1"
  59 --   parse error at (line 1, column 1):
  60 --   unexpected "1"
  61 --   expecting "-"
  62 --
  63 --   >>> parseTest hyphen "x"
  64 --   parse error at (line 1, column 1):
  65 --   unexpected "x"
  66 --   expecting "-"
  67 --
  68 hyphen :: Parser Hyphen
  69 hyphen = char '-' >> return Hyphen