LSD account for a train arrival-departure protocol

/*****************************************************************************
	file 	: 	train.lsd
	date	: 	12/14/94
	author	: 	Simon Yun Pui Yung ('modernised' by wmb)
	notes	: 	description of agents for a `railway arrival-departure' system
******************************************************************************/

The stationmaster

---

agent sm() {

oracle	(time) Limit, Time,		// knowledge of time to elapse before departure due
	(bool) guard_raised_flag,	// knowledge of whether the guard has raised his flag
	(bool) driver_ready,		// knowledge of whether the driver is ready
	(bool) around[d],		// knowledge of whether there's anybody around doorway
	(bool) door_open[d]; 	// the open/close status of door d (for d = 1 .. number_of_doors)

state	(time) tarrive = |time|,	// the S-M registers time of arrival
	(bool) can_move,		// the signal observed by driver for starting engine
	(bool) whistle = false,		// the whistle is not blowing
	(bool) whistled = false,	// the whistle has not blown
	(bool) sm_flag = false,		// S-M lowers flag
	(bool) sm_raised_flag = false;	// S-M has not raised flag

handle	(bool) can_move,
	(bool) whistle,
	(bool) whistled,
	(bool) sm_flag,
	(bool) sm_raised_flag;
	(bool) door_open[d];	// the open/close status of door d (for d = 1 .. number_of_doors)

derivate
			number_of_doors
	(bool) ready =	    /\	(!door_open[d]);	// are all doors shut?
			  d = 1
	(bool) timeout = (Time - tarrive) > Limit;	// departure due

protocol
	door_open[d] ^ !around[d] -> door_open[d] = false; (d = 1 .. number_of_doors)
	ready ^ timeout ^ !whistled -> whistle = true; whistled = true; guard(); whistle = false;
	ready ^ whistled ^ !sm_raised_flag -> sm_flag = true; sm_raised_flag = true;
	sm_flag ^ guard_raised_flag -> sm_flag = false;
	ready ^ guard_raised_flag ^ driver_ready ^ engaged ^ !can_move -> can_move = true;

}

---

The guard

---

agent guard() {

oracle	(bool) whistled, sm_raised_flag, brake;

state	(bool) guard_raised_flag = false,
	(bool) guard_flag = false,
	(bool) brake;

handle	(bool) guard_raised_flag, guard_flag;

derivate	LIVE = engaging || whistled;

protocol
	engaging -> brake = true; running = false;
	sm_raised_flag ^ brake -> brake = false; guard_flag = true; guard_raised_flag = true;
	guard_flag ^ !sm_flag -> guard_flag = false;

}

---

The driver

---

agent driver() {

oracle	(bool) can_move, engaged, whistled;
	(position) at, from;

handle	(position) to, from,
	(bool) running,
	(bool) driver_ready = false;

state	(bool) driver_ready = false,
	(position) from;

protocol
	whistled ^ !driver_ready -> driver_ready = true;
	engaged ^ from <> at -> from = at; to = next_station_after(at);
	can_move ^ engaged -> driver_ready = false; running = true;

}

---

The passenger

---

agent passenger((int) p, (int) d, (position) _from, (position) _to) {
// passenger p intending to travel from station _from to station _to
// and he will access through door d of the train

oracle	(position) at,
	(bool) door_open[d];

state	(bool) pos[p] = OUT_DOOR, alighting[p], boarding[p], join_queue[p,d];

handle	(position) from[p] = _from;
	(position) to[p] = _to;
	(int) door[p] = d;
	(bool) pos[p],
	(bool) door_open[d];

derivate
	alighting[p] = at == to[p] ^ pos[p] != OUT_DOOR && engaged;
	boarding[p] = at == from[p] ^ pos[p] != IN_DOOR && engaged;
	join_queue[p,d] = (alighting[p] ^ door_open[d] ^ pos[p] == IN_DOOR) ||
		(boarding[p] ^ door_open[d] ^ pos[p] == OUT_DOOR);
	LIVE = !(at == to[p] ^ pos[p] == ON_PLATFORM);

protocol
	at == to[p] ^ pos[p] == AT_SEAT -> pos[p] = IN_DOOR;
	alighting[p] ^ !door_open[d] -> door_open[d] = true;
	alighting[p] ^ pos[p] == AT_DOOR ^ door_open[d] ^ !queuing[d]
		-> pos[p] == OUT_DOOR; door_open[d] = false; pos[p] = ON_PLATFORM;
	alighting[p] ^ pos[p] == AT_DOOR ^ door_open[d] ^ queuing[d]
		-> pos[p] == OUT_DOOR; pos[p] = ON_PLATFORM;
	boarding[p] ^ !door_open[d] -> door_open[d] = true;
	boarding[p] ^ pos[p] == AT_DOOR ^ door_open[d] ^ !queuing[d]
		-> pos[p] = IN_DOOR; door_open[d] = false; pos[p] = AT_SEAT;
	boarding[p] ^ pos[p] == AT_DOOR ^ door_open[d] ^ queuing[d]
		-> pos[p] = IN_DOOR; pos[p] = AT_SEAT;

}

---

The train

---

agent train() {

state	(bool) running = true,
	(bool) brake = false,
	(bool) door_open[d] = false, (d = 1 .. number_of_doors)
	(position) from = station1,
	(position) to = station2,
	(position) at = some_position,
	(bool) engaging, engaged, leaving, alert;

handle	(bool) alert;

derivate
	(bool) engaging = running ^ to == at,
	(bool) leaving = running ^ from == at,
	(bool) engaged = !running;

protocol
	engaging ^ !alert -> alert = true; guard(); sm();
	leaving ^ alert -> alert = false; delete guard(), sm();

}

---

The door

---

agent door((int) d) {

oracle	(int) pos[p], door[p]; (p = 1 .. number_of_passengers)

state	(bool) queuing[d], occupied[d], around[d];

derivate
	queuing[d] = there exists p such that join_queue[p,d] == true;
	occupied[d] = there exists p such that (pos[p] == AT_DOOR ^ door[p] == d)
	around[d] = there exists p such that (door[p] == d ^
		(pos[p] == IN_DOOR || pos[p] == AT_DOOR || pos[p] == OUT_DOOR))

protocol	queuing[d] ^ !occupied[d] ^ join_queue[p,d] == true
		-> pos[p] = AT_DOOR; (p = 1 .. number_of_passengers)
}