sub _hdlr_perl {
     my($ctx, $args) = @_;
     my $tokens = $ctx->stash('tokens');
     my $builder = $ctx->stash('builder');
     my $res = '';
     defined(my $out = $builder->build($ctx, $tokens))
         or return $ctx->error($builder->errstr);
     $res = eval $out;
     return $@ if $@;
     $res;
  }