function abc() {
  if (some_condition) {
    message('blah');
    return; // early exit
  }
  // otherwise do stuff
}

function check_condition() {
  if (some_condition) {
    message('blah');
    return false; // early exit
  }
  else
    return true;
}

function abc() {
  if (!check_condition()) {return;}

  // otherwise do stuff
}