Pass the Parcel specification game[preparetopass12,pass12,preparetopass23,pass23, preparetopass34,pass34,preparetopass41,pass41, musicstop,musicstart,present] :exit (* Pass the Parcel Game *) (* M. Calder 1999 *) (* represent passing by two events:preparetopass and pass *) (* if music stops during passing, i.e. after prepare but before pass *) (* the intended recipient unwraps the parcel *) library boolean endlib (***********************) (* The Parcel ADT *) (***********************) type Parcel is boolean sorts Parcel opns wrappers : Parcel -> bool new : -> Parcel add : Parcel -> Parcel unwrap : Parcel ->Parcel initial : Parcel eqns forall p:Parcel ofsort bool wrappers(new) = false; wrappers(add(p)) = true; ofsort Parcel Uuwrap(add(p)) = p; unwrap(new) = new; initial = wrap(wrap(wrap(new))); endtype (***********************) (* Basic Player Process*) (***********************) process Player[preparetoreceive,receive,preparetopass,pass, musicstop,musicstart,present](parcel?:bool) :exit := [parcel?] -> HasParcel[preparetoreceive,receive,preparetopass,pass, musicstop,musicstart,present](initial) [] [not (parcel?)] -> (present; exit [] HasnoParcel[preparetoreceive,receive,preparetopass,pass, musicstop,musicstart,present]) endproc

(*********************) (* Player Has Parcel *) (*********************) process HasParcel[prepr,receive,prepp,pass,stop,start,win](p:Parcel) :exit := (* p is the parcel *) (* music is playing, player is about to pass the parcel *) (* pass the parcel: 3 possibilities *) (* i) pass the parcel interrupted by music stop *) (* ii) pass the parcel, no interruptions *) (* iii) music stops before parcel passing commences *) (prepp; (stop; pass!p; ((win; exit) [] (start; HasnoParcel[prepr,receive,prepp,pass,stop,start,win])) [] (pass!p; HasnoParcel[prepr,receive,prepp,pass,stop,start,win]))) [] (* music stops before beginning to pass *) (* unwrap the parcel and win if no wrappers left *) (let newp:Parcel = unwrap(p) in (stop; i; ([not(wrappers(newp))] -> (win; exit) [] (start; HasParcel[prepr,receive,prepp,pass,stop,start,win](newp))))) endproc

(*******************************) (* Player Does Not Have Parcel *) (*******************************) process HasnoParcel[prepr,receive,prepp,pass,stop,start,win]:exit := (* music is playing, player is about receive the parcel *) (* receive the parcel: 3 possibilities *) (* i) parcel passing interrupted by music stop, *) (* unwrap the parcel after receipt and exit if no wrappers left*) (* ii) receive the parcel, no interruptions *) (* iii) music stops before parcel passing commences*) (prepr; ((stop; receive?p:Parcel; i; (let newp:Parcel = unwrap(p) in ([not(wrappers(newp))] -> (win; exit) [] (start; HasParcel[prepr,receive,prepp,pass,stop,start,win](newp))))) [] (receive?p:Parcel; HasParcel[prepr,receive,prepp,pass,stop,start,win](p)))) [] (* music stops before parcel received *) (* don't actually receive anything *) (stop; ((win; exit) [] (start; HasnoParcel[prepr,receive,prepp,pass,stop,start,win]))) endproc (*****************************) (* Music *) (*****************************) process Music[start,stop] :exit := stop; (exit [] start; Music[start,stop]) endproc

(*******************************) (* A Game with 4 Players *) (*******************************) process FourPlayer[preparetopass12,pass12,preparetopass23,pass23, preparetopass34,pass34,preparetopass41,pass41, musicstop,musicstart,present] : exit := (((Player[preparetopass41,pass41,preparetopass12,pass12, musicstop,musicstart,present](true) |[preparetopass12,pass12,musicstop,musicstart,present]| Player[preparetopass12,pass12,preparetopass23,pass23, musicstop,musicstart,present](false)) |[preparetopass23,pass23,musicstop,musicstart,present]| Player[preparetopass23,pass23,preparetopass34,pass34, musicstop,musicstart,present](false)) |[preparetopass34,pass34,perparetopass41,pass41,musicstop,musicstart,present]| Player[preparetopass34,pass34,preparetopass41,pass41, musicstop,musicstart,present](false) ) |[musicstart,musicstop]| (musicstart; Music[musicstart,musicstop]) endproc endspec