[ZPT] Possible changes to path-related

[Guido van Rossum]

> From: "Guido van Rossum" <guido@digicool.com>
> > Evan, it would seem that you need changes to the TAL interpreter to
> > implement cancellation of actions, right?  Have you done this yet?
> 
> I have an untested implementation in my sandbox.  I can check it in if you
> would be willing to finish/correct/test it today or tomorrow.

I have some time.  Instead of checking it in, can you send me a
tarball of the relevant directories?  (I can do the diffs myself. :-)

> > I'm a bit uncomfortable with the three-way possible outcomes (do it,
> > exception, or cancel), and with the scope of cancellation if
> > multiple actions are placed on the same element.
> 
> I'm not sure what you mean.  I expect that any of the three outcomes might
> be desired under different circumstances, and that per-action granularity is
> a requirement (replace attribute A if a value exists for it, but replace
> attribute B no matter what you do with A).

I guess I'd like to see a clearer specification of what cancellation
means.  I also guess that once I see your source code it will be
obvious.  My code maps relatively cleanly on the existing semantics.

> > I'm not at all sure I like the use of "if" in this syntax -- the
> > placement of "if" in the guts of the expression to control the whole
> > statement makes me think of Perl. :-)  But I don't have an
> > alternative... :-(
> 
> Neither do I.  There are lots of ways I can think of to spell it, none of
> them great. This at least has the virtue of being short and reading fairly
> well.

And it's less confusing because we refrained from using "if" in the
TAL syntax. :-)

--Guido van Rossum (home page: http://www.python.org/~guido/)