X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=src%2FXml.hs;h=95eddc0e51f949acbb287003dfb98c22ff244cb4;hb=5124833f973f6c47a4eda3f4e343d3d8631897c6;hp=96ba0116e184986b7b0a1942a5d96c002eb860db;hpb=9fff5c185dd7a2c8655815f36b72736d61401e41;p=dead%2Fhtsn-import.git

diff --git a/src/Xml.hs b/src/Xml.hs
index 96ba011..95eddc0 100644
--- a/src/Xml.hs
+++ b/src/Xml.hs
@@ -4,61 +4,43 @@
 --
 module Xml (
   DtdName(..),
-  ToFromXml(..),
+  FromXml(..),
   parse_opts,
-  pickle_unpickle )
+  pickle_unpickle,
+  unpickleable )
 where
 
-import Database.Groundhog ( AutoKey )
+import Control.Exception ( SomeException(..), catch )
 import Text.XML.HXT.Core (
   (>>>),
   (/>),
+  PU,
   SysConfigList,
   XmlPickler(..),
   hasName,
-  no,
   readDocument,
   runX,
-  withPreserveComment,
   withRemoveWS,
-  withSubstDTDEntities,
-  withValidate,
   xpickleVal,
   xunpickleVal,
   yes )
 
 
--- | A typeclass for types which can be converted into an associated
---   XML type. The story behind this is long, but basically, we need
+-- | A typeclass for XML types that can be converted into an associated
+--   database type. The story behind this is long, but basically, we need
 --   to different types for each XML thingie we're going to import: a
 --   database type and an XML type. Both Groundhog and HXT are very
 --   particular about the types that they can use, and there's no way
 --   to reuse e.g. a type that HXT can pickle in Groundhog. So this
---   typeclass gives us a way to get the XML type from the Groundhog
---   type.
+--   typeclass gives us a way to get the database type from the XML
+--   type that we have to define for HXT.
 --
---   At first there appears to be an equally-valid approach, getting the
---   Groundhog type from the XML one. But Groundhog won't use type family
---   instances, so here we are.
---
-class ToFromXml a where
-  -- | Each instance a must declare its associated XML type (Xml a)
-  type Xml a :: *
-  type Container a :: *
-
-  -- | And provide a function for getting an (Xml a) out of an "a."
-  to_xml :: a -> Xml a
-
-  -- | And provide a function for getting an "a" out of an (Xml a).
-  from_xml :: Xml a -> a
+class FromXml a where
+  -- | Each instance a must declare its associated database type (Db a)
+  type Db a :: *
 
-  -- | Often we need to provide a key to use as a foreign key into
-  --   some container. If the instance "belongs" to some other object,
-  --   then it might need to be passed a key before it can un-XML
-  --   itself. For example, the XML version of 'NewsTeam' doesn't
-  --   contain a message ID which is part of its database type.
-  from_xml_fk :: AutoKey (Container a) -> Xml a -> a
-  from_xml_fk _ = from_xml
+  -- | And provide a function for getting a (Db a) out of an "a".
+  from_xml :: a -> Db a
 
 
 -- | Represents the DTD filename ("SYSTEM") part of the DOCTYPE
@@ -66,18 +48,11 @@ class ToFromXml a where
 newtype DtdName = DtdName String
 
 -- | A list of options passed to 'readDocument' when we parse an XML
---   document. We don't validate because the DTDs from TSN are
---   wrong. As a result, we don't want to keep useless DTDs
---   areound. Thus we disable 'withSubstDTDEntities' which, when
---   combined with "withValidate no", prevents HXT from trying to read
---   the DTD at all.
+--   document. All cosmetic whitespace should be removed, otherwise we
+--   have to parse it in each pickler.
 --
 parse_opts :: SysConfigList
-parse_opts =
-  [ withPreserveComment no,
-    withRemoveWS yes,
-    withSubstDTDEntities no,
-    withValidate no ]
+parse_opts = [ withRemoveWS yes ]
 
 
 -- | Given a root element name and a file path, return both the
@@ -91,6 +66,11 @@ parse_opts =
 --   to 'xpickle' would be ambiguous. By returning some @a@s, we allow
 --   the caller to annotate its type.
 --
+--   Note that this will happily pickle nothing to nothing and then
+--   unpickle it back to more nothing. So the fact that the
+--   before/after results from this function agree does not mean that
+--   the document was successfully unpickled!
+--
 pickle_unpickle :: XmlPickler a
                 => String
                 -> FilePath
@@ -98,7 +78,7 @@ pickle_unpickle :: XmlPickler a
 pickle_unpickle root_element filepath = do
   -- We need to check only the root message element since
   -- readDocument produces a bunch of other junk.
-    expected <- runX $ arr_getobj
+    expected <- runX arr_getobj
     actual <- runX $ arr_getobj
                      >>>
                      xpickleVal xpickle
@@ -112,3 +92,20 @@ pickle_unpickle root_element filepath = do
                    hasName root_element
                    >>>
                    xunpickleVal xpickle
+
+
+
+-- | Is the given XML file unpickleable? Unpickling will be attempted
+--   using the @unpickler@ argument. If we unilaterally used the
+--   generic 'xpickle' function for our unpickler, a type ambiguity
+--   would result. By taking the unpickler as an argument, we allow
+--   the caller to indirectly specify a concrete type.
+--
+unpickleable :: XmlPickler a => FilePath -> PU a -> IO Bool
+unpickleable filepath unpickler = do
+  xmldoc <- try_unpickle `catch` (\(SomeException _) -> return [])
+  return $ (not . null) xmldoc
+  where
+    try_unpickle = runX $ readDocument parse_opts filepath
+                          >>>
+                          xunpickleVal unpickler