I have modified the contextString.pl file (which is used by the parserPopUp.pl macros) to correct the issue. The problem was that the parser was looking for numbers before strings, and that matched "0, 2" and "2, 3" but not "-1, 2" or "-2, 2" because negation is an operator and not part of the number itself. (That is so that 5-2 is subtraction and not 5*(-2).)
You can get the updated contextString.pl from the CVS repoistory.
Davide
WeBWorK Problems
Can't call method "strings" on an undefined value
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