[Aimmath-developers] SafeParse.mpl, aim/TextQuestion.mpl changes

[Greg G. <gr...@ma...>]

Dear AIM developers,

Several times this semester students have encountered nasty errors
during validation, and on one occasion I had to track through the
logs to find out what the student had entered, because it didn't even
make it to the question history.

This sort of problem used to arise because the result of Maple's
parse command is an unevaluated expression, and so it is quite
possible to have an expression that parses ok but is not in fact
valid Maple (because it is not possible to evaluate it), e.g.
[2,3][4,5] is such a case ... when Maple comes to evaluate it,
it runs into an indexing error.

To combat this problem I added an extra 'Status' possibility to
`aim/SafeParse`, namely "Evaluation error", and now the function
`aim/TextQuestion/BasicValidation` checks this possibility and
exits cleanly. An assignment of the parse report value was also
moved later in the function to avoid an impossible evaluation.

  Regards,
  Greg