Other languages: Difference between revisions

Since version 1.2.7 of ProB (July 2008) you can also open Promela files with ProB. This mode is still experimental but already very usable and provides source-level highlighting during animation. The main purpose is to debug and animate Promela specifications in a user-friendly way. We do not plan to compete in terms of model checking speed with Spin (Spin compiles Promela to C code, ProB uses a Prolog interpreter). To animate a Promela model, simply open the file with the .pml or .prom extension with the "File->Open..." command. You will have to choose "Other Formalisms" or "All Files" in the filter pop-up-menu to be able to select the file.

You can also use ProB to animate and model check other specification languages by writing your own Prolog interpreter. To do this you should create a Prolog file with the .P extension and which defines three predicates:

• trans/3: this predicate should compute for every state (second argument), the outgoing transitions (first argument), and the resulting new states (third argument)
• prop/2: this predicate should compute the properties for the states of your system
• start/1: this defines the initial states of your system

For example, the following defines a system with two states (a and b) and two transitions (lock and unlock):

start(a). trans(lock,a,b). trans(unlock,b,a). prop(X,X).

These Prolog files can be loaded with ProB's open command (be sure to use the .P extension and to either choose "All files" or "Other Formalisms" in the file filtering menu).

Another simple example for a very basic process algebra is as follows:

% start(PossibleInitialState)
start(choice(pref(a,stop),intl(pref(b,pref(c,stop)),pref(d,stop)))).

% trans(Event, StateBefore, StateAfter)
trans(A,pref(A,P),P). % action prefix
trans(A,intl(P,Q),intl(P2,Q)) :- trans(A,P,P2). % interleave
trans(A,intl(P,Q),intl(P,Q2)) :- trans(A,Q,Q2).
trans(A,par(P,Q),par(P2,Q2)) :- trans(A,P,P2), trans(A,Q,Q2). % parallel composition
trans(A,choice(P,Q),P2) :- trans(A,P,P2). % choice
trans(A,choice(P,Q),Q2) :- trans(A,Q,Q2).

% prop(State, PropertyOfState)
prop(pref(A,P),prefix).
prop(intl(P,Q),interleave).
prop(A,A).

If you have a working interpreter, you can also contact the ProB developers in order for your interpreter to be included in the standard ProB distribution (in the style of the CSP-M or Promela interpreters). With this you can add syntax highlighting, error highlighting in the source code, highlighting during animation, support for new LTL properties,...

Another, slightly more elaborate example, is the following interpreter for regular expressions:

/* A simple animator for regular expressions */

start('|'('.'('*'(a),b) ,  '.'('*'(b),a))). 

trans(_,[],_) :- !,fail.
trans(X,X,[]) :- atomic(X),!.
trans(X,'|'(R1,R2),R) :- 
 trans(X,R1,R) ; trans(X,R2,R).
trans(X,'.'(R1,B),R) :- trans(X,R1,R2),
 gen_concat(R2,B,R).
trans(X,'?'(R1),R) :-
 trans(X,R1,R) ; (X=epsilon,R=[]).
trans(epsilon,'*'(_R1),[]). 
trans(X,'*'(R1),R) :- 
 trans(X,R1,R2),
 gen_concat(R2,'*'(R1),R).
trans(X,'+'(R1),R) :- 
 trans(X,R1,R2),
 gen_concat(R2,'*'(R1),R).

gen_concat(R1,R2,R) :- 
 (R1=[] -> R = R2 ; R = '.'(R1,R2)).

prop(X,X).

Finally, a more complex example is an encoding of the Rush Hour puzzle which also includes a graphical visualisation (using the animation_function_result predicate recognised by ProB as of version 1.4.0-rc3).