Re: Can there be two?

> Having read this bit and also the PoD you posted I was wondering if it
> would be possible to take the op-tree you describe and compile to some
> other language similar to the way that Jemplate works.

Absolutely.

The "optree" is an arrayref of arrayrefs.  The execute_tree method which runs
the tree looks like this:

sub execute_tree {
    my ($self, $tree, $out_ref) = @_;

    # node contains (0: DIRECTIVE,
    #                1: start_index,
    #                2: end_index,
    #                3: parsed tag details,
    #                4: sub tree for block types
    #                5: continuation sub trees for sub continuation block 
types (elsif, else, etc)
    #                6: flag to capture next directive
    for my $node (@$tree) {
        ### text nodes are just the bare text
        if (! ref $node) {
            warn "NODE: TEXT\n" if trace;
            $$out_ref .= $node if defined $node;
            next;
        }

        warn "NODE: $node->[0] (char $node->[1])\n" if trace;
        $$out_ref .= $self->debug_node($node) if $self->{'_debug_dirs'} && ! 
$self->{'_debug_off'};

        my $val = $DIRECTIVES->{$node->[0]}->[1]->($self, $node->[3], $node, 
$out_ref);
        $$out_ref .= $val if defined $val;
    }
}

The $DIRECTIVES table looks like this:

    $DIRECTIVES = {
        #name       #parse_sub       #play_sub        #block   #postdir 
#continue #move_to_front
        BLOCK   => [\&parse_BLOCK,   \&play_BLOCK,    1,       0,       0,      
  
1],
        BREAK   => [sub {},          \&play_control],
        CALL    => [\&parse_CALL,    \&play_CALL],
        CASE    => [\&parse_CASE,    undef,           0,       0,       
{SWITCH => 1, CASE => 1}],
        CATCH   => [\&parse_CATCH,   undef,           0,       0,       {TRY 
=> 1, CATCH => 1}],
        CLEAR   => [sub {},          \&play_CLEAR],
     .... };

I will probably change those back to be pure overridable method lookups 
instead of listing the callbacks in the table.  That would allow you to 
subclass CGI::Ex::Template and override each of the "play" blocks.

Or you can do arbitrary things with the optree.

Paul