Finalizing D2

Daniel Keep daniel.keep.lists at
Sun May 24 09:51:43 PDT 2009

Michel Fortin wrote:
> ...
> A callback API isn't necessarily SAX. A callback API doesn't necessarily
> have to parse everything until completion, it could parse only the next
> token and call the appropriate callback.

When I talk "callback api," I mean something fundamentally like SAX.
The reason is that if your callback api only does a single callback, all
you've really done is move the switch statement inside the function call
at the cost of having to define a crapload of functions outside of it.

> If I can construct a range class/struct over my callback API I'll be
> happy. And if I can recursively call the parser API inside a callback
> handler so I can reuse the call stack while parsing then I'll be very
> happy.

I don't see how constructing a range over a callback api will work.
Callback apis are inversion of control, ranges aren't.

As for using a callback api recursively, that just seems like a lot of
work to replicate the way a pull api works in the first place.

>> Something like Tango's PullParser is the superior API because although
>> it's more verbose up-front, that's as bad as it gets.  Plus, you can
>> actually do stuff like call subroutines.
> All that is needed really is a callback system that parses only one
> token. Then the callback can update the PullParser state, or the
> token-range state, run in a loop to produce a SAX-like API, or directly
> do what you want to do, which may include parsing more tokens using
> different callbacks until you reach a closing tag.

Like I said, this seems like a lot of work to bolt a callback interface
onto something a pull api is designed for.

At best, you'll end up rewriting this:

> foreach( tt ; pp )
> {
>     switch( tt )
>     {
>         case XmlTokenType.StartElement: blah(; break;
>         ...
>     }
> }

to this:

> pp.parse
> (
>     XmlToken(Type.StartElement, {blah(;}),
>     ...
> );

Except of course that you now can't easily control the loop, nor can do
you do fall-through on the cases.

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