("-backend",Arg.Set_string(Globals.backend), "Backend directory");
("-frontend",Arg.Tuple[Arg.String(fun s->cur_dir:=s);
Arg.String(fun s->cur_slice:=s;
("-backend",Arg.Set_string(Globals.backend), "Backend directory");
("-frontend",Arg.Tuple[Arg.String(fun s->cur_dir:=s);
Arg.String(fun s->cur_slice:=s;