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 wrapper around 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 newtype Hyphen = Hyphen Char
  32
  33
  34 -- | Equality is defined semantically (all hyphens are equal).
  35 --
  36 --   ==== _Examples_
  37 --
  38 --   >>> let h1 = Hyphen '-'
  39 --   >>> let h2 = Hyphen '-'
  40 --   >>> h1 == h2
  41 --   True
  42 --
  43 --   If you do something stupid, that's your fault:
  44 --
  45 --   >>> let h1 = Hyphen '-'
  46 --   >>> let h2 = Hyphen 'x'
  47 --   >>> h1 == h2
  48 --   True
  49 --
  50 instance Eq Hyphen where _ == _ = True
  51
  52
  53 -- | 'Show' is defined semantically; all hyphens display as \'-\'.
  54 --   The implementation is based on what GHC derives, discovered via
  55 --   @ghci -ddump-deriv@.
  56 --
  57 --   ==== _Examples_
  58 --
  59 --   >>> let h = Hyphen '-'
  60 --   >>> h
  61 --   Hyphen '-'
  62 --
  63 --   If you do something stupid, that's your fault:
  64 --
  65 --   >>> let h = Hyphen 'x'
  66 --   >>> h
  67 --   Hyphen '-'
  68 --
  69 instance Show Hyphen where
  70   showsPrec d _ =
  71     showParen (d > application_precedence) (showString "Hyphen '-'")
  72     where
  73       application_precedence = 10
  74
  75
  76 -- | 'Pretty' is defined semantically; all hyphens display as \'-\'.
  77 --
  78 --   ==== _Examples_
  79 --
  80 --   >>> let h = Hyphen '-'
  81 --   >>> pretty_print h
  82 --   -
  83 --
  84 --   If you do something stupid, that's your fault:
  85 --
  86 --   >>> let h = Hyphen 'x'
  87 --   >>> pretty_print h
  88 --   -
  89 --
  90 instance Pretty Hyphen where pretty_show _ = "-"
  91
  92
  93 -- | Parse a single hyphen and wrap it in our 'Hyphen' type.
  94 --
  95 --   ==== _Examples_
  96 --
  97 --   >>> import Text.Parsec ( parseTest )
  98 --
  99 --   Hyphens are parsed:
 100 --
 101 --   >>> parseTest hyphen "-"
 102 --   Hyphen '-'
 103 --
 104 --   But not letters or digits:
 105 --
 106 --   >>> parseTest hyphen "1"
 107 --   parse error at (line 1, column 1):
 108 --   unexpected "1"
 109 --   expecting "-"
 110 --
 111 --   >>> parseTest hyphen "x"
 112 --   parse error at (line 1, column 1):
 113 --   unexpected "x"
 114 --   expecting "-"
 115 --
 116 hyphen :: Parser Hyphen
 117 hyphen = fmap Hyphen (char '-')