Properly handle negative constants and variables.

[dpvc]

This PR resolves the issue raised in the WeBWorK forum where the LimitedPolynomial context didn't rule out certain expressions that should not be allowed. These turned out to be cause by not handling negation properly.

To test, use

loadMacros("contextLimitedPolynomial.pl");
Context("LimitedPolynimal-Strict");
Compute("-2 + x + 4");
Compute("-x + x");

Both of the Compute() statements should produce error messages (without the patch, they will produce formula objects.

[Alex-Jordan]

@drgrice1 Should this be retargeted to 2.16?

[Alex-Jordan]

Tested with Davide's suggestion, and I see the bug before this commit. After this commit, the bug is gone.

[drgrice1]

I am getting Unknown context 'LimitedPolynimal-Strict' with your test code!

Other than that everything works as claimed.

I think this should be targeted for 2.16.

[dpvc]

Sorry, should be LimitedPolynomial-strict. (Lower case "strict")

[drgrice1]

@dpvc: Yeah, I know. I guess the exclamation mark wasn't enough to indicate that I was kidding.

Thanks for the fix.

I am going to re-target this for PG 2.16 and merge it if that is okay. It will also be added to develop of course.

[dpvc]

OK, sounds good.

[drgrice1]

... or nevermind on the re-target. I will merge it, and then add it to PG 2.16. It seems this branch doesn't want to re-target cleanly.