$correct = 5; $sol = $correct->num_cmp(checker => sub { my ($correctgiven, $input) = @_; if ($input == $correctgiven) { return 5; } if ($input == -$corretgiven) { return -5; } return $input; }); #(this is line 35)But this doesn't work and the error message I get is
Can't call method "cmp" without a package or object reference at line 35 of [TMPL]/settest/problem1.I think I might be failing to put my variables in the proper Context() or something. I'm not sure of how to do that in any case.
First, your correct answer is a plain perl number, not a perl object, and in particular, not a MathObject. You should use
$correct = Real(5);
for that (being sure to have loaded MathObjects.pl in your loadMacros() call at the top of the file).
Next, for a MathObject, you don't use num_cmp or fun_cmp or any of the older answer checkers directly. Instead, you use the cmp method of the MathObject, since it knows its own type, and can tell what type of answer checking you need:
$correct->cmp(...);
Next, the return value for your checker routine should be 0 or 1, depending on whether the student's answer is correct or not. You seem to be returning the student's answer instead. (Technically, you can give partial credit by giving a decimal value between 0 and 1. I don't remember wether the return value is clipped to that range, but it might be that returning -5 would take AWAY points.)
Finally, that cmp method returns an AnswerEvaluator object, and that needs to be passed to ANS() to make it active. The usual method would be to do something like
ANS($correct->cmp(...));
So for your case, something like:
ANS(Real(5)->cmp(checker => sub {
my ($correct,$student) = @_;
return $correct == $student || $correct == -$student;
}));
should do the trick.
There are a number of samples in this discussion forum. See, for example:
https://webwork.maa.org/moodle/mod/forum/discuss.php?d=5637
https://webwork.maa.org/moodle/mod/forum/discuss.php?d=4308
https://webwork.maa.org/moodle/mod/forum/discuss.php?d=5421
https://webwork.maa.org/moodle/mod/forum/discuss.php?d=5736
You can also look at the pg/macros/answerCustom.pl file for some examples and documentation. See the PG file POD documentation for formatted versions of the comments within the files. There are some sections on MathObjects, for example, that will give you a start (though these files are woefully incomplete). The answerCustom.pl file is documented there, as are all the main PG macro files.
Hope that helps.
Davide
Variable 'Q' is not defined in this context; see position 9 of formula at line 36 of [TMPL]/settest/problem2b.pg Died within main::Formula called at line 36 of [TMPL]/settest/problem2b.pg
Problem2 ERROR caught by Translator while processing problem file:settest/problem2b.pg **************** Variable 'Q' is not defined in this context; see position 9 of formula at line 36 of [TMPL]/settest/problem2b.pg Died within main::Formula called at line 36 of [TMPL]/settest/problem2b.pg ****************
Context()->variables->add(Q=>'Real');
so that Q is recognized as a variable.
Also, note that your custom checker is not really needed since al it does is exactly what the default checker does. No need to do the quality check yourself unless you are planning to do something more complicated.
Hope that helps out.
Davide