[WWcvs] pg: Added a routine to trap errors in a function call.

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

Log Message:
-----------
Added a routine to trap errors in a function call.  I've needed this
for a long time, and got tired of working around the lack by hacks
involving PG_restricted_eval, which can't handle local variables from
the calling function.  This addition is still safe because it is
passed code (not a string) and the code is already compiled in the
safe compartment, so it can't include the disallowed commands.

Now I need to go back to remove the hacks from the various pg/macros
files where they currently exist.

Tags:
----
rel-2-4-patches

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

Revision Data
-------------
Index: WeBWorK.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Value/WeBWorK.pm,v
retrieving revision 1.11.6.1
retrieving revision 1.11.6.1.2.1
diff -Llib/Value/WeBWorK.pm -Llib/Value/WeBWorK.pm -u -r1.11.6.1 -r1.11.6.1.2.1
--- lib/Value/WeBWorK.pm
+++ lib/Value/WeBWorK.pm
@@ -32,10 +32,24 @@
 }
 
 #
+#  Call a subtroutine with error trapping.
+#  (We need to be able to do this from custom
+#   answer checkers and other MathObject code.
+#   PG_restricted_eval is not sufficient for this
+#   since that uses a string and so can't access
+#   local variables from the calling routine.)
+#
+sub Eval {
+  my $f = shift;
+  return unless defined($f);
+  eval {&$f(@_)};
+}
+
+#
 #  Remove backtrace and line number, since these
 #  will be reported in the student message area.
 #
-sub Parser::reportEvalError {
+sub reportEvalError {
   my $error = shift; my $fullerror = $error;
   $error =~ s/ at \S+\.\S+ line \d+(\n|.)*//;
   $error =~ s/ at line \d+ of (\n|.)*//;