XmlReader and recursive descent parsers

[Jon Shemitz]

I just wrote my second method that reads an XML stream with XmlReader
and spits out a instance of an object that represents the XML stream.
In effect, this was a simple recursive descent parser that uses the
XmlReader as a tokenizer.

Realizing this naturally led to the question: Are there any tools
which would let me supply a description of the domain semantics
(perhaps in XSD) and which would construct a parser shell that can
turn a (say) <Foo> element into an instance of a Foo object, leaving
me only the task of parsing the attributes and storing child elements
in the proper fields?

I did a few Google searches that didn't turn up anything, but that's
never very conclusive ....

--

www.midnightbeach.com

[Oleg Tkachenko [MVP]]

Jon Shemitz wrote:

Realizing this naturally led to the question: Are there any tools
which would let me supply a description of the domain semantics
(perhaps in XSD) and which would construct a parser shell that can
turn a (say) <Foo> element into an instance of a Foo object, leaving
me only the task of parsing the attributes and storing child elements
in the proper fields?

Sounds like you are talking about XmlSerializer.

--
Oleg Tkachenko [XML MVP, MCAD]
http://www.xmllab.net
http://blog.tkachenko.com

[Jon Shemitz]

"Oleg Tkachenko [MVP]" wrote:

Realizing this naturally led to the question: Are there any tools
which would let me supply a description of the domain semantics
(perhaps in XSD) and which would construct a parser shell that can
turn a (say) <Foo> element into an instance of a Foo object, leaving
me only the task of parsing the attributes and storing child elements
in the proper fields?

Sounds like you are talking about XmlSerializer.

No, not quite. XmlSerializer will save and restore an object (if
you're lucky): I'm looking for a parser generator that knows about the
XML structure but that makes no assumptions about the data structure
you build from it.

--

www.midnightbeach.com

[Oleg Tkachenko [MVP]]

Jon Shemitz wrote:

No, not quite. XmlSerializer will save and restore an object (if
you're lucky): I'm looking for a parser generator that knows about the
XML structure but that makes no assumptions about the data structure
you build from it.

Aha, sort of "typed XmlReader". There were some talks before, but I
haven't heard of any implementattions yet. The problem is that the
benefits are still unclear - why do you need it?

--
Oleg Tkachenko [XML MVP, MCAD]
http://www.xmllab.net
http://blog.tkachenko.com

[Jon Shemitz]

"Oleg Tkachenko [MVP]" wrote:

Aha, sort of "typed XmlReader". There were some talks before, but I
haven't heard of any implementattions yet. The problem is that the
benefits are still unclear - why do you need it?

For much the same reasons that one uses a parser generator instead of
building a parser by hand: It takes less time to write, it takes less
time to debug, and it's easier to verify.

I spent hours getting my most recent XmlReader code to handle child
elements properly. Partly that was because my XmlWriter code was
putting a wholly unnecessary <contents></contents> layer around child
elements, but partly that was because I had trouble keeping track of
all the possible Next States. I kept running into assertion violations
or even infinite loops.

Not my happiest few hours!

--

www.midnightbeach.com

[Oleg Tkachenko [MVP]]

Jon Shemitz wrote:

For much the same reasons that one uses a parser generator instead of
building a parser by hand: It takes less time to write, it takes less
time to debug, and it's easier to verify.

I spent hours getting my most recent XmlReader code to handle child
elements properly. Partly that was because my XmlWriter code was
putting a wholly unnecessary <contents></contents> layer around child
elements, but partly that was because I had trouble keeping track of
all the possible Next States. I kept running into assertion violations
or even infinite loops.

I'm curious what API and behaviour would you expect from such "typed
XmlReader"?

--
Oleg Tkachenko [XML MVP, MCAD]
http://www.xmllab.net
http://blog.tkachenko.com

[Jon Shemitz]

"Oleg Tkachenko [MVP]" wrote:

I'm curious what API and behaviour would you expect from such "typed
XmlReader"?

Oh, there's a pretty wide range, there, I suppose. Something like
Coco/R's annotated grammar would make some sense - a way to add
arbitrary C# code at the points in the grammar where the generator
would create a method. That way, you could update the grammar (if you
didn't get it right the first time) and regenerate the parser without
losing all your actions.

I don't have the widest experience with parser generators - there
might be other schemes that make more sense - but Coco/R's is pretty
straightforward. Sure was better than Visual Parse's vile reduction
function.

--

www.midnightbeach.com