Okay, so maybe we should open this to other options: should we get rid of
preparsing "\" into "BackslashOperator"?
For what it's worth, I removed the line defining `_backslash_` in
binary_tree.py and and I only say one doctest failure in any obvious places
(combinat and thematic_tutorials). So it's not even used much. Same for
matroids.
I think that using \ to escape characters in strings still works, but
line-continuation does not: in Sage, these fail:
sage: a = 3 + \
and
sage: \
whereas in pure Python, such backslashes would be treated as
line-continuations. It should be possible to fix this while keeping the
current preparser behavior for "\" in the middle of a line. Or as Nils
proposes, getting rid of the current preparser behavior should also solve
it.
On Wednesday, September 27, 2023 at 2:44:19 PM UTC-7 Nils Bruin wrote:
> I'm quite strongly against because it collides with a well-established
> meaning of `\` in python: escape character. It's used to avoid command
> termination by newline in things like formulas (as "\<newline", which gets
> parsed as whitespace rather than command termination outside of brackets).
>
> I'm in fact rather shocked that `\` in sage already doesn't work as it's
> supposed to in python but instead gets substituted as "BackslashOperator()".
>
> Searching the codebase currently only shows "_backslash_" implemented on
> matroid, matrix, and binary_tree, so extinguishing it should be doable. We
> should definitely not entrench its use further.
>
> If you want to write your denominator first, you can already do ~2 * 3 . I
> think that's already sufficiently perverse that we don't need another way
> to spell that.
> On Wednesday, 27 September 2023 at 12:16:57 UTC-7 David Joyner wrote:
>
>> On Wed, Sep 27, 2023 at 2:32 PM John H Palmieri <jhpalm...@gmail.com>
>> wrote:
>>
>>> The github issue #36060 (https://github.com/sagemath/sage/issues/36060)
>>> proposes adding a backslash operator for Sage integers, so that "2 \ 3"
>>> will return the same as "3 / 2". Do you support this?
>>>
>>>
>> I'm not for or against. However, I don't see the problem that
>> implementing this "\" is going to solve. The ticket suggests that users
>> will naturally type 2\3 instead of 3/2, if I am reading between the lines
>> correctly.
>>
>>
>>> BackslashOperator is defined in "sage/misc/misc.py", and the preparser
>>> converts "A \ b" to the appropriate Python code. The docstring for
>>> BackslashOperator says "Implements Matlab-style backslash operator for
>>> solving systems A \ b".
>>>
>>> It seems pretty innocuous to me — in fact I don't care much either way —
>>> but since Sage integers are so ubiquitous, it seems like a good idea to ask
>>> before implementing it.
>>>
>>> --
>>> John
>>>
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>>>
>>
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