Oh boy every once in a while, this sort of code shows up:

on $*:text:/\b(msg|join|part)\s(\43\S+)\b/iS:?:{
  if ($istok(join part,$regml(1),32)) { 
    $regml(1) $regml(2) 
  }
  else { msg $regml(2) $strip($$3-) }
}

You gotta make sure the $2 entered starts with the chantype "#" or it can be anything else to result an error. This is best done with regex as shown per my example.