[WWcvs] pg: Report bad function calls in student Formulas (e.g., roots of negatives), which used to be silently marked as incorrect.

[dpvc v. a. <we...@ma...>]

Log Message:
-----------
Report bad function calls in student Formulas (e.g., roots of
negatives), which used to be silently marked as incorrect.  This is
done during the post-processing phase by calling the formula's reduce
method, which will return an error if there are illegal function calls
(or other errors).

Modified Files:
--------------
    pg/lib/Value:
        AnswerChecker.pm

Revision Data
-------------
Index: AnswerChecker.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Value/AnswerChecker.pm,v
retrieving revision 1.119
retrieving revision 1.120
diff -Llib/Value/AnswerChecker.pm -Llib/Value/AnswerChecker.pm -u -r1.119 -r1.120
--- lib/Value/AnswerChecker.pm
+++ lib/Value/AnswerChecker.pm
@@ -1624,7 +1624,7 @@
 
 sub cmp_call_filter {
   my $ans = shift; my $method = shift;
-  return $ans->{correct_value}->$method($ans);
+  return $ans->{correct_value}->$method($ans,@_);
 }
 
 sub cmp_prefilter {
@@ -1681,8 +1681,10 @@
 
 sub cmp_postprocess {
   my $self = shift; my $ans = shift;
-  return unless $ans->{score} == 0 && !$ans->{isPreview};
-  return if $ans->{ans_message};
+  return unless $ans->{score} == 0;
+  eval {$ans->{student_formula}->reduce} if defined($ans->{student_formula}); # check for bad function calls
+  $self->cmp_error($ans) if $self->{context}{error}{flag};                    #  and report the error
+  return if $ans->{ans_message} || $ans->{isPreview};
   if ($self->{domainMismatch} && $ans->{showDomainErrors}) {
     $self->cmp_Error($ans,"The domain of your function doesn't match that of the correct answer");
     return;