1 {-# LANGUAGE TypeFamilies #-}
3 -- | General XML stuff.
12 import Database.Groundhog ( AutoKey )
13 import Text.XML.HXT.Core (
31 -- | A typeclass for types which can be converted into an associated
32 -- XML type. The story behind this is long, but basically, we need
33 -- to different types for each XML thingie we're going to import: a
34 -- database type and an XML type. Both Groundhog and HXT are very
35 -- particular about the types that they can use, and there's no way
36 -- to reuse e.g. a type that HXT can pickle in Groundhog. So this
37 -- typeclass gives us a way to get the XML type from the Groundhog
40 -- At first there appears to be an equally-valid approach, getting the
41 -- Groundhog type from the XML one. But Groundhog won't use type family
42 -- instances, so here we are.
44 class ToFromXml a where
45 -- | Each instance a must declare its associated XML type (Xml a)
49 -- | And provide a function for getting an (Xml a) out of an "a."
52 -- | And provide a function for getting an "a" out of an (Xml a).
53 from_xml :: Xml a -> a
55 -- | Often we need to provide a key to use as a foreign key into
56 -- some container. If the instance "belongs" to some other object,
57 -- then it might need to be passed a key before it can un-XML
58 -- itself. For example, the XML version of 'NewsTeam' doesn't
59 -- contain a message ID which is part of its database type.
60 from_xml_fk :: AutoKey (Container a) -> Xml a -> a
61 from_xml_fk _ = from_xml
64 -- | Represents the DTD filename ("SYSTEM") part of the DOCTYPE
66 newtype DtdName = DtdName String
68 -- | A list of options passed to 'readDocument' when we parse an XML
69 -- document. We don't validate because the DTDs from TSN are
70 -- wrong. As a result, we don't want to keep useless DTDs
71 -- areound. Thus we disable 'withSubstDTDEntities' which, when
72 -- combined with "withValidate no", prevents HXT from trying to read
75 parse_opts :: SysConfigList
77 [ withPreserveComment no,
79 withSubstDTDEntities no,
83 -- | Given a root element name and a file path, return both the
84 -- original unpickled root "object" and the one that was constructed
85 -- by pickled and unpickling the original. This is used in a number
86 -- of XML tests which pickle/unpickle and then make sure that the
87 -- output is the same as the input.
89 -- We return the object instead of an XmlTree (which would save us
90 -- an unpickle call) because otherwise the type of @a@ in the call
91 -- to 'xpickle' would be ambiguous. By returning some @a@s, we allow
92 -- the caller to annotate its type.
94 pickle_unpickle :: XmlPickler a
98 pickle_unpickle root_element filepath = do
99 -- We need to check only the root message element since
100 -- readDocument produces a bunch of other junk.
101 expected <- runX $ arr_getobj
102 actual <- runX $ arr_getobj
108 return (expected, actual)
110 arr_getobj = readDocument parse_opts filepath