sub given($&) {
  ($_,$code) = @_;
  {
    local $match = 0;
    $code->();
  }
}

sub when($&) {
  my ($test,$code) = @_;
  if(/$test/) {
    $code->() ;
    $match=1;
  }
}

sub default(&) {
  my ($code) = @_;
  $code->() unless($match):
}