--- loncom/interface/lonhelper.pm	2003/04/11 17:45:37	1.7
+++ loncom/interface/lonhelper.pm	2003/04/11 18:16:04	1.8
@@ -1,7 +1,7 @@
 # The LearningOnline Network with CAPA
 # .helper XML handler to implement the LON-CAPA helper
 #
-# $Id: lonhelper.pm,v 1.7 2003/04/11 17:45:37 bowersj2 Exp $
+# $Id: lonhelper.pm,v 1.8 2003/04/11 18:16:04 bowersj2 Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -30,10 +30,6 @@
 # (.helper handler
 #
 
-# FIXME: Change register calls to register with the helper.
-# Then have the helper reg and unreg the tags.
-# This removes my concerns about breaking other code.
-
 =pod
 
 =head1 lonhelper - HTML Helper framework for LON-CAPA
@@ -794,8 +790,6 @@ You can mix and match methods of creatin
 "push" onto the choice list, rather then wiping it out. (You can even 
 remove choices programmatically, but that would probably be bad form.)
 
-FIXME: Document and implement <exec> and <condition> in the element package.
-
 =cut
 
 no strict;
@@ -1721,5 +1715,96 @@ sub postprocess {
 
 1;
 
+package Apache::lonhelper::general;
+
+=pod
+
+=head2 General-purpose tag: <exec>
+
+The contents of the exec tag are executed as Perl code, not inside a 
+safe space, so the full range of $ENV and such is available. The code
+will be executed as a subroutine wrapped with the following code:
+
+"sub { my $helper = shift; my $state = shift;" and
+
+"}"
+
+The return value is ignored.
+
+$helper is the helper object. Feel free to add methods to the helper
+object to support whatever manipulation you may need to do (for instance,
+overriding the form location if the state is the final state; see 
+lonparm.helper for an example).
+
+$state is the $paramHash that has currently been generated and may
+be manipulated by the code in exec. Note that the $state is not yet
+an actual state B<object>, it is just a hash, so do not expect to
+be able to call methods on it.
+
+=cut
+
+BEGIN {
+    &Apache::lonhelper::register('Apache::lonhelper::general',
+                                 'exec', 'condition', 'clause');
+}
+
+sub start_exec {
+    my ($target,$token,$tagstack,$parstack,$parser,$safeeval,$style)=@_;
+
+    if ($target ne 'helper') {
+        return '';
+    }
+    
+    my $code = &Apache::lonxml::get_all_text('/exec', $parser);
+    
+    $code = eval ('sub { my $helper = shift; my $state = shift; ' .
+        $code . "}");
+    &$code($helper, $paramHash);
+}
+
+sub end_exec { return ''; }
+
+=pod
+
+=head2 General-purpose tag: <condition>
+
+The <condition> tag allows you to mask out parts of the helper code
+depending on some programatically determined condition. The condition
+tag contains a tag <clause> which contains perl code that when wrapped
+with "sub { my $helper = shift; my $state = shift; " and "}", returns
+a true value if the XML in the condition should be evaluated as a normal
+part of the helper, or false if it should be completely discarded.
+
+The <clause> tag must be the first sub-tag of the <condition> tag or
+it will not work as expected.
+
+=cut
+
+# The condition tag just functions as a marker, it doesn't have
+# to "do" anything. Technically it doesn't even have to be registered
+# with the lonxml code, but I leave this here to be explicit about it.
+sub start_condition { return ''; }
+sub end_condition { return ''; }
+
+sub start_clause {
+    my ($target,$token,$tagstack,$parstack,$parser,$safeeval,$style)=@_;
+
+    if ($target ne 'helper') {
+        return '';
+    }
+    
+    my $clause = Apache::lonxml::get_all_text('/clause', $parser);
+    $clause = eval('sub { my $helper = shift; my $state = shift; '
+        . $clause . '}');
+    if (!&$clause($helper, $paramHash)) {
+        # Discard all text until the /condition.
+        &Apache::lonxml::get_all_text('/condition', $parser);
+    }
+}
+
+sub end_clause { return ''; }
+
+1;
+
 __END__