Separate the Network.DNS.RBL.Weight module and fix the doctests.

[dead/harbl.git] / harbl / src / Network / DNS / RBL / Weight.hs

diff --git a/harbl/src/Network/DNS/RBL/Weight.hs b/harbl/src/Network/DNS/RBL/Weight.hs
new file mode 100644 (file)
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+++ b/harbl/src/Network/DNS/RBL/Weight.hs
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+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
+-- | The 'Weight' type, its instances, and a Parsec parser to parse
+--   one off the end of a 'Site'.
+--
+--   This is a simple newtype wrapper around an 'Int', meant to be
+--   used wherever a weight or an RBL score is intended (to prevent
+--   integer mixups). For example, the RBLs are all weighted with
+--   'Weight's, and when a user supplied a \"badness\" threshold, it
+--   will be as a 'Weight' as well. The two are then comparable but
+--   not with other 'Int's.
+--
+module Network.DNS.RBL.Weight (
+  Weight(..),
+  weight )
+where
+
+import Text.Parsec (
+  (<|>),
+  char,
+  digit,
+  many1,
+  option,
+  try,
+  unexpected )
+import Text.Parsec.String ( Parser )
+import Text.Read ( readMaybe )
+
+import Network.DNS.RBL.Pretty ( Pretty(..) )
+
+
+-- | The 'Weight' wrapper around an 'Int. We use
+--   GeneralizedNewtypeDeriving to derive num automatically (so that we
+--   can sum these things).
+--
+--   ==== _Examples_
+--
+--   >>> let w1 = Weight 1
+--   >>> w1
+--   Weight 1
+--   >>> let w2 = Weight 1
+--   >>> w1 == w2
+--   True
+--   >>> let w3 = Weight 2
+--   >>> w1 == w3
+--   False
+--   >>> sum [w1, w2, w3]
+--   Weight 4
+--
+newtype Weight = Weight Int deriving (Eq, Num, Show)
+
+
+-- | Pretty-print a 'Weight'. This just shows/prints the underlying 'Int'.
+--
+--   ==== _Examples_
+--
+--   >>> pretty_print $ Weight 17
+--   17
+--
+instance Pretty Weight where
+  pretty_show (Weight w) = show w
+
+
+-- | Parse the weight multiplier off the end of an input 'Site'. This
+--   expects there to be a \"multiplier\" character (an asterisk)
+--   before the integral weight.
+--
+--   ==== _Examples_
+--
+--   >>> import Text.Parsec ( parseTest )
+--
+--   Negative, zero, and positive integers are all supported:
+--
+--   >>> parseTest weight "*-5"
+--   Weight (-5)
+--
+--   >>> parseTest weight "*0"
+--   Weight 0
+--
+--   >>> parseTest weight "*17"
+--   Weight 17
+--
+--   If the weight is empty, it defaults to @1@:
+--
+--   >>> parseTest weight ""
+--   Weight 1
+--
+--   The default is used whenever parsing fails:
+--
+--   >>> parseTest weight "*hello"
+--   Weight 1
+--
+--   The 'Pretty' instance works as intended:
+--
+--   >>> import Text.Parsec ( parse )
+--   >>> pretty_print $ parse weight "" "*3"
+--   3
+--
+weight :: Parser Weight
+weight = try parse_weight <|> return (Weight 1)
+  where
+    parse_weight = do
+      _ <- char '*'
+      sign <- (char '-') <|> (option '+' (char '+'))
+      w <- many1 digit
+      case ( readMaybe w :: Maybe Int ) of
+        -- If "many1 digit" gives us a list of digits, we should be able
+        -- to convert that to an Int! It will overflow rather than fail
+        -- if the input is too big/small, so it should really always
+        -- succeed.
+        Nothing -> unexpected "weight: readMaybe failed on a sequence of digits!"
+        Just k  -> return $ Weight (if sign == '-' then negate k else k)