LSD account for a Cat Flap

/*******************************************************************
	file 	: 	catflap.lsd
	date	: 	07.08.91
	author	: 	I.Bridge (as 'modernised' by wmb 11/11/97)
	notes	: 	description of agents for a 'catflap' system
********************************************************************/

TYPE
	flapPosTyp = ENUM (fpOut, fpVert, fpIn)
	lockPosTyp = SET OF ENUM (lpOut, lpIn)
	catIntTyp  = ENUM (ciGoOut, ciStayPut, ciGoIn)
	pushDirTyp = ENUM (pdOut, pdIn)

---

AGENT flap {
STATE
	lockPos	: lockPosTyp
	flapPos	: flapPosTyp
ORACLE
	lockPos
	pushDir
HANDLE
	flapPos
PROTOCOL
	(pushDir == pdOut) AND NOT (lpOut IN lockPos)
		-> flapPos = fpOut	/* open out */
	(pushDir == pdIn) AND NOT (lpIn IN lockPos)
		-> flapPos = fpIn	/* open in */
	(pushDir == pdNone)
		-> flapPos = fpVert	/* close */
}

---

AGENT man {
ORACLE
	flapPos
HANDLE
	lockPos
PROTOCOL
	(flapPos = fpVert) 		/* change lock */
		-> lockPos IN power_set(lockPosTyp) /* See Notes */
}

---

AGENT cat {
STATE
	catInt	: catIntTyp
	catPos	: INTEGER	// > 0 : outside
				// = 0 : at flap
				// < 0 : inside
	pushDir	: pushDirTyp
ORACLE
	flapPos
HANDLE
	pushDir
DERIVATE
	catEngag is (catPos >= 1) && (catPos <= 1);
	catObstr is (flapPos == fpVert)
PROTOCOL
	(catInt = ciGoIn) AND catObstr		/* push in */
		-> pushDir = pdIn
	(catInt = ciGoIn) AND NOT catObstr	/* walk in */
		-> catPos = catPos - 1
	(catInt = ciGoOut) AND catObstr 	/* push out */
		-> pushDir = pdOut
	(catInt = ciGoOut) AND NOT catObstr	/* walk out */
		-> catPos = catPos + 1
	NOT catEngag				/* no push */
		-> pushDir = pdNone
	TRUE					/* decide intention */
		-> intent IN catIntTyp
}

Notes :

The cat is engaged in getting through the flap when it is at or within a unit distance from the entrance (at position 0). Whilst engaged in the flap the cat must push in the direction required to open the flap or to keep it open. The feature of cat length has not been modelled.

Cat behaviour is totally non-deterministic (modelling an extremely fickle cat). The model is sufficiently realistic to encompass the eventuality that the cat changes its intentions whilst engaged in the flap (guaranteeing a safe outcome for the cat).

The function 'power_set' is assumed to return an instance of the power set of a set of values defined by a type.