parse fractions in numeric answers about prairielearn HOT 7 CLOSED

Is this still just a wish-list item? I seem to have more and more students attempting to enter fractions.

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@cdschmit are the students doing this on v2 or v3 questions? We've tried to mitigate the issue in v3, but I'm open to revisiting this issue if it's still a problem.

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Hmmm...Yeah, I think it is a V2 problem. In v3, does it evaluate? I'll update it and see what happens.

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In v3 it currently doesn't evaluate, but it tells students that it's invalid and it lets them try again with no penalty (doesn't count as a grading attempt).

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On the one hand, this is a small change to eliminate a pain point.

On the other hand, if you allow fractions, then why not other mathematical expressions like cos(1) or exp(-2) or 3^4 (equivalently 3**4)?

I think we'd have to implement even fractions in a similar way to how pl-symbolic-input works - safe evaluation by walking the AST.

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Maybe an easy option would be for pl-number-input to allow both floating-point and rational numbers, where the format for a rational number must be of the form m / n. Maybe that's already what you were thinking. That's a trivial change.

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For some reason (experience with other platforms) it does seem that some students expect to be able to type fractions into numeric answer boxes. Is it easy to implement this without pulling in all of sympy? Just special-casing strings with a / in them?

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