if(defined $q->param('form_submitted')){
  if(&errors){ #Error occured
    &display_form($q);
  }else{
    &thank_you;
  }
}else{
  &display_form;
}

sub display_form(){
  ##Do form stuff
}

##</code><code>##

$temp = HTML::Template->new(
                      file => 'file.tmpl',
                      associate => $q
              );