[WWcvs] pg: Fixed a bug where if you specified a variable other than dx, the

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

Log Message:
-----------
Fixed a bug where if you specified a variable other than dx, the
division by zero check didn't work properly.

Modified Files:
--------------
    pg/macros:
        parserDifferenceQuotient.pl

Revision Data
-------------
Index: parserDifferenceQuotient.pl
===================================================================
RCS file: /webwork/cvs/system/pg/macros/parserDifferenceQuotient.pl,v
retrieving revision 1.2
retrieving revision 1.3
diff -Lmacros/parserDifferenceQuotient.pl -Lmacros/parserDifferenceQuotient.pl -u -r1.2 -r1.3
--- macros/parserDifferenceQuotient.pl
+++ macros/parserDifferenceQuotient.pl
@@ -52,10 +52,10 @@
     $dx . '|' . $context->{_variables}->{pattern};
   $context->update;
   $context->variables->add($dx=>'Real');
-  $dx = bless $self->SUPER::new($formula), $class;
-  $dx->{isValue} = 1; $dx->{isFormula} = 1;
+  $q = bless $self->SUPER::new($formula), $class;
+  $q->{isValue} = 1; $q->{isFormula} = 1; $q->{dx} = $dx;
   main::Context($current);  # put back the original context;
-  return $dx;
+  return $q;
 }
 
 sub cmp_class {'a Difference Quotient'}
@@ -66,10 +66,10 @@
 )}
 
 sub cmp_postprocess {
-  my $self = shift; my $ans = shift;
+  my $self = shift; my $ans = shift; my $dx = $self->{dx};
   return if $ans->{score} == 0 || $ans->{isPreview};
   $main::__student_value__ = $ans->{student_value};
-  my ($value,$err) = main::PG_restricted_eval('$__student_value__->reduce(dx=>0)');
+  my ($value,$err) = main::PG_restricted_eval('$__student_value__->substitute('.$dx.'=>0)->reduce');
   $self->cmp_Error($ans,"It looks like you didn't finish simplifying your answer")
     if $err && $err =~ m/division by zero/i;
 }