On Sun, Nov 9, 2008 at 3:07 PM, William Stein <[EMAIL PROTECTED]> wrote:
> On Sun, Nov 9, 2008 at 2:04 PM, Justin C. Walker <[EMAIL PROTECTED]> wrote:
>>
>> Hi,
>>
>> On Nov 9, 2008, at 13:27 , [EMAIL PROTECTED] wrote:
>>
>>> Hello I tried the folowing three links (from sage-devel) on my
>>> computer as well as on sagenb.com
> ^^^^^^^^^^^^^^^^^
>
> That's a good hint. I just tried this on sagenb.org, and indeed
> in sage-3.1.4 in the *notebook* implicit multiplication is broken.
> I've made this
>
> http://trac.sagemath.org/sage_trac/ticket/4485
>
> Note implicit multiplication still works fine on the command line.
>
> It's possible implicit multiplication never worked in the notebook; I
> have no idea. I'll try for a few minutes right now to fix this.
> William
OK, I've thought about it, and see now that there is no way
that implicit multiplication was ever even *implemented*
for the notebook! Just to illustrate what is going on, note
that if in the notebook you type
implicit_multiplication(True)
preparse('3x')
you get as output
'Integer(3)*x'
which illustrates that the implicit_multiplication command works fine
in the actual Sage worksheet process. The problem is that the
preparsing of the input for each cell of the notebook is *not* done in
that subprocess! It's done by the worksheet server process itself,
before the input is ever sent to the subprocess.
There are some approaches to fixing this and I'm not happy really
about any of them:
1. Make it so the whole notebook server has an
implicit_multiplication mode. This is absurd since some users might
want it and some not. Alternatively, make it so the notebook server
has a mode flag for each worksheet. That's bad too since that mode
can't be set via user input (by typing in cells) unless we fully parse
all input before passing it on for evaluation -- i.e., that's a stupid
idea which will result in great pain. The other option, would be to
have some GUI checkbox or something, and just give an error if one
types in the input box "implicit_multiplication". This would be
inconsistent and maybe busy, but would probably work. The
inconsistency would be huge, since, e.g., if somebody writes a 30 line
script like this:
...
implicit_multiplication(True)
...
3x + 1
...
and just *pastes* it into the notebook, it will suddenly not work.
Which will be really annoying.
2. Change how the Sage notebook evaluates code blocks. Instead of
preparsing input before sending it off to be evaluated by the
worksheet subprocess, somehow send a chunck of non-preparsed code off,
and a command that says "preparse this then evaluate it".
3. Make sage query the subprocess for its implicit_multiplication
state before every single evaluation -- this would be idiotic and slow
down the server a lot. Not an option.
I think 2 is the best option, but it will not be easy to implement,
and making this change scares me. It feels like the sort of change
that could introduce numerous subtle bugs, and result in nontrivial
degredation in functionality -- for example, maybe source code ??
inspection of user-defined functions in the notebook might no longer
work.
Incidentally, here is a workaround to make it so you can input an
expression using implicit multiplication in the notebook.
implicit_multiplication(True)
sage_eval('3x^3 + 4/5 x + 1', globals())
3*x^3 + 4*x/5 + 1
I'm not going to do anything further on this without some feedback
from Robert Bradshaw (who implemented implicit multiplication)
and/or Mike Hansen who I think knows the relevant part of the
notebook code well enough to have a comment about what
I wrote above.
-- William
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