I usually work in this way:

# CGI::Application code...

# The main runmode, where I show the page
#
sub foo
{
    my $self = shift;
    my $s    = $self->session();

    my $tmpl = $self->load_tmpl('foo');

    # ... load data in the template, as long
    # as the missing and invalid fields, that
    # come from the session (see foo_update()).

    foo_view( $tmpl, $data, $s->param('missing'), $s->param('invalid')
+);

    return $tmpl->output();
}

sub foo_update
{
    my $self = shift;
    my $q    = $self->query();
    my $s    = $self->session();

    my %form = $q->Vars();                                            
+          
    my $results = Data::FormValidator->check( \%form, $profile );     
+          
                                                                      
+          
    if ($results->has_invalid() or $results->has_missing()) {         
+          
                                                                      
+          
        $s->param( missing => [ $results->missing() ] ,               
+          
                   invalid => [ $results->invalid() ] );              
+          
                                                                      
+          
        $self->redirect( { rm => 'foo' } );                           
+          
    }                                                                 
+          
    else {                                                            
+          
                                                                      
+          
        # Data are good, we proceed...                                
+          
        $self->redirect( { rm => 'bar' } );                           
+          
    }                                                                 
+          
}
[download]

Then I setup a View module, that receives the template object, data and the invalid and missing fields, like this:

# This is called by foo() from the main application, just before
# to display the page
#
sub foo_view
{
    my $template   = shift;
    my $date       = shift;
    my $missing    = shift;
    my $invalid    = shift;

    $template->param( "missing_$_" => 1 ) for @$missing;
    $template->param( "invalid_$_" => 1 ) for @$invalid;

    # [...]

    return $template;
}
[download]

Finally, in the template, I can write things like that:

<TMPL_IF invalid_some_field>Bad boy! This is an error message.</TMPL_I
+F>
[download]

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