X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=src%2FXml.hs;h=2f68dd09c661de44048f78fe0a45314fe4d38b98;hb=a163a47ab0aed0072f7868d4b2b28aa4c326e5e1;hp=dfb6d055ac0e297b94d42d92eff810e1464d42ec;hpb=fee0cee55b87fd717b04d065b6f68162b6138a4a;p=dead%2Fhtsn-import.git

diff --git a/src/Xml.hs b/src/Xml.hs
index dfb6d05..2f68dd0 100644
--- a/src/Xml.hs
+++ b/src/Xml.hs
@@ -3,15 +3,19 @@
 -- | General XML stuff.
 --
 module Xml (
+  DtdName(..),
   ToFromXml(..),
   parse_opts,
-  pickle_unpickle )
+  pickle_unpickle,
+  unpickleable )
 where
 
+import Control.Exception ( SomeException(..), catch )
 import Database.Groundhog ( AutoKey )
 import Text.XML.HXT.Core (
   (>>>),
   (/>),
+  PU,
   SysConfigList,
   XmlPickler(..),
   hasName,
@@ -59,6 +63,11 @@ class ToFromXml a where
   from_xml_fk :: AutoKey (Container a) -> Xml a -> a
   from_xml_fk _ = from_xml
 
+
+-- | Represents the DTD filename ("SYSTEM") part of the DOCTYPE
+--   definition.
+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
@@ -85,6 +94,11 @@ 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
@@ -106,3 +120,20 @@ 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