Re: [Haskell-cafe] Incremental XML parsing with namespaces?

9 Jun 2009

      On Mon, Jun 8, 2009 at 3:39 PM, Henning
Thielemann wrote:
...
I think you could use the parser as it is and do the name parsing later.
Due to lazy evaluation both parsers would run in an interleaved way.
I've been trying to figure out how to get this to work with lazy
evaluation, but haven't made much headway. Tips? The only way I can
think of to get incremental parsing working is to maintain explicit
state, but I also can't figure out how to achieve this with the
parsers I've tested (HaXml, HXT, hexpat).

Here's a working example of what I'm trying to do, in Python. It reads
XML from stdin, prints events as they are parsed, and will terminate
when the document ends:

##########################

from xml.sax import handler, saxutils, expatreader

class ContentHandler (handler.ContentHandler):
	def __init__ (self):
		self.events = []
		self.level = 0

	def startElementNS (self, ns_name, lname, attrs):
		self.events.append (("BEGIN", ns_name, lname, dict (attrs)))
		self.level += 1

	def endElementNS (self, ns_name, lname):
		self.events.append (("END", ns_name, lname))
		self.level -= 1

	def characters (self, content):
		self.events.append (("TEXT", content))

def main ():
	parser = expatreader.ExpatParser ()
	content = ContentHandler ()
	parser.setFeature (handler.feature_namespaces, True)
	parser.setContentHandler (content)
	got_events = False
	while content.level > 0 or (not got_events):
		text = raw_input ("Enter XML:\n")
		parser.feed (text)
		print content.events
		content.events = []
		got_events = True

if __name__ == "__main__": main()

###############################

$ python incremental.py
Enter XML:
<test xmlns="urn:test"><test2><test3>
[('BEGIN', (u'urn:test', u'test'), u'test', {}), ('BEGIN',
(u'urn:test', u'test2'), u'test2', {}), ('BEGIN', (u'urn:test',
u'test3'), u'test3', {})]
Enter XML:
</test3></test2><test2 a="b"/>text content goes here
[('END', (u'urn:test', u'test3'), None), ('END', (u'urn:test',
u'test2'), None), ('BEGIN', (u'urn:test', u'test2'), u'test2', {(None,
u'a'): u'b'}), ('END', (u'urn:test', u'test2'), None), ('TEXT', u'text
content goes here')]
Enter XML:
</test>
[('END', (u'urn:test', u'test'), None)]

#############################

As demonstrated, the parser retains state (namespaces, nesting)
between text inputs. Are there any XML parsers for Haskell that
support this incremental behavior?

Re: [Haskell-cafe] Incremental XML parsing with namespaces?

John Millikin