MathObject version of the new Boolean context

macros/contexts/contextReaction.pl

@@ -276,6 +276,23 @@ sub cmp_postprocess {
 		if $ans->{showTypeWarnings} && $ans->{student_value}{tree}->type ne 'Reaction';
 }
 
+# permit ions to be written at 2+ or simply + or -
+# automatically added with cmp_call_filter (hence the additional argument)
+sub cmp_prefilter {
+	my $self = shift;    # technically, this is correct_value
+	my $ans  = shift;
+	# parens are added by MQ when the ion digit leads - swap the order
+	$ans->{student_ans} =~ s/\^\((\d)([+-])\)/"^(".$2.$1.")"/ge;
+	# no parens when the ion digit is preceeded by +/-,
+	# modification is necessary to protect against next regex
+	$ans->{student_ans} =~ s/\^([+-])(\d)/"^(".$1.$2.")"/ge;
+	# only ions with no digits remain
+	$ans->{student_ans} =~ s/\^\(([+-])\)/"^(".$1."1)"/ge;
+	$ans->{student_ans} =~ s/\^([+-])/"^(".$1."1)"/ge;
+	warn "modified reaction: $ans->{student_ans}";
+	return $ans;
+}
+
 #
 #  Since the context only allows things that are comparable, we
 #  don't really have to check anything.  (But if somone added