#5251: [with patch, needs review] preparser bug in parsing the backslash "solve
right" notation
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Reporter: was | Owner: mhansen
Type: defect | Status: assigned
Priority: major | Milestone: sage-3.3
Component: misc | Resolution:
Keywords: |
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Comment (by was):
{{{
22:57 < wstein> mhansen -- Hi -- I posted some remarks on #5251
22:58 < mhansen> I'm reading them now.
22:58 < wstein> I'm ashamed of how bad the preparser is on \.
22:58 < wstein> It's all my fault, of course.
22:58 < wstein> I also just wrote Robertwb to ask him to comment on the
ticket... even though that
might mean waiting for his
22:58 < wstein> feedback until Monday.
23:02 < mhansen> One quick fix on the safe side would be to eliminate the
stopping condition. That's
how I figured it was implemented anyway. I only thought
a simple "A \ x" syntax was
supported.
23:02 < wstein> A\x + B\y would be a disaster.
23:02 < wstein> Of course, it already is :-)
23:02 < mabs> :)
23:02 < wstein> sage: preparse(r'A\x + B\y')
23:02 < wstein> 'A._backslash_(x + B)._backslash_(y)'
23:03 < mhansen> Obviously no one has used it for anything too involved
:-)
23:03 < wstein> without the stopping, we would have
23:03 < wstein> sage: preparse(r'v = A\x # find the solution')
23:03 < wstein> 'v = A._backslash_(x )# find the solution'
23:03 < wstein> oops
23:03 < wstein> that's now
23:03 < wstein> we would have
23:03 < wstein> 'v = A._backslash_(x # find the solution)'
23:04 < wstein> I wonder if we should deprecate it?
23:04 < wstein> I like the feature, but the implementation is so bad.
23:04 < wstein> And doing it right might be quite hard.
23:04 < wstein> Also, it clearly can't be used that much...
23:05 < mhansen> I would probably throw in a deprecation warning until we
do a proper fix.
23:05 < wstein> Use, I definitely mean by deprecate that there would be a
deprecation warning.
23:05 < mhansen> Just so anyone who uses it knows there are "issues".
23:05 < wstein> Yep.
23:05 < wstein> How to do it -- ?
23:05 < wstein> One way would be to add something to A._backslash_
23:05 < wstein> The other would be to actually make the preparser itself
emit a warning as it preparses.
23:05 < wstein> The latter would be more robust.
23:06 < mhansen> That was what I was envisioning.
23:06 < wstein> It's possible other code already in preparser.py can be
used though to quickly fix this
problem well.
23:06 < wstein> Robertwb wrote is particularly good at this sort of thing,
being a "compiler guy".
23:06 < mhansen> Agreed. He has some other improvements to the preparser
at #5106.
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5251#comment:3>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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