AR (Action Rules) The Language, Implementation, and Applications A tutorial given at CICLOPS’06

AR (Action Rules)The Language, Implementation, and ApplicationsA tutorial given at CICLOPS’06 Neng-Fa Zhou CUNY Brooklyn College and Graduate Center CICLOPS'06

Evolution from freeze to AR • Early delay constructs • freeze in Prolog-IIfreeze(X,p(X,Y)) • When declarations in NU-Prolog:-p(X,Y) when X. • Block and when in Sicstus Prolog :-block p(-,?).when(nonvar(X),p(X,Y)) CICLOPS'06

Evolution from freeze to AR(Cont.) • Delay clauses in Sepia (Eclipse)delay and(X,Y,Z) if var(X),var(Y),X\==Y,Z\==1 • Action rules (B-Prolog)p(X,Y),var(X),{ins(X)} => q(X,Y). Allows for the description of not only delay conditions but also activating events and actions CICLOPS'06

Sources of this tutorial • N.-F. Zhou: Programming Finite-Domain Constraint Propagators in Action Rules, Theory and Practice of Logic Programming, accepted 2005. • N.-F. Zhou, M.Wallace, and P.J. Stuckey: The dom Event and its Use in Implementing Constraint Propagators, Technical Report, CUNY Computer Science, 2006. • T. Schrijvers, N.-F. Zhou, and B. Demoen: Translating Constraint Handling Rules into Action Rules, CHR'06. • N.-F. Zhou: A Constraint-based Graphics Library for B-Prolog, Software - Practice and Experience, 2003. CICLOPS'06

Outline • The AR language • Syntax and semantics of action rules • Events • Applications • Co-routining and concurrency • Constraint propagation • Compiling CHR • Interactive graphical user interfaces • The implementation • Conclusion CICLOPS'06

The AR languageSyntax • Action rules • Agentp(X1,…,Xn) • Condition • Inline tests (e.g., var(X),nonvar(X),X==Y,X>Y) • EventSet • event(X,O) -- a general form event • ins(X) -- X is instantiated • Action • Same as a clause body • A predicate can contain multiple action rules Agent, Condition, {EventSet} => Action CICLOPS'06

The AR languageSyntax (Cont.) • Commitment rules • An action rule degenerates into a commitment rule if no event is specified • Example append([],Ys,Zs) => Ys=Zs. append([X|Xs],Ys,Zs) => Zs=[X|Zs1], append(Xs,Ys,Zs1). CICLOPS'06

The AR languageOperational semantics Agent, Condition, {EventSet} => Action • An agent (subgoal) A is suspended if: • A matches Agent, and • Condition is true • A is activated when an event in EventSet is posted • Action is executed when A is activated and Condition is true • A is suspended again after Action is executed • The next rule is tried if Condition fails • Afails if Action fails CICLOPS'06

Events • General form events • event(X,O) • X – channel variable • O – event object • Example echo(X),{event(X,O)}=>writeln(O). • ins(X) • X is instantiated • Example (freeze(X,q(X,Y)) )p(X,Y),var(X),{ins(X)}=>true. P(X,Y)=>q(X,Y). CICLOPS'06

Posting events • A channel expression is • A channel variable X • A conjunction of variables: X1 /\ X2 … /\ Xn • A disjunction of variables: X1 \/ X2 … \/ Xn • Posting events • post_event(C,O) • C is a channel expression • post_ins(X) • Post an ins(X) event CICLOPS'06

Example An echoing agent echo(X),{event(X,O)} => writeln(O). ?-echo(X),post_event(X,hello). hello ?-echo(X),repeat,post_event(X,hello),fail. hello hello hello … CICLOPS'06

Killing agents • An agent vanishes after a commitment rule is applied to it echo(Flag,X),var(Flag), {event(X,O),ins(Flag)} => writeln(O). echo(Flag,X) => true. ?-echo(Flag,X),post_event(X,hello),Flag=1. hello CICLOPS'06

Co-routining and concurrency freeze(X,G) freeze(X,G), var(X), {ins(X)} => true. freeze(X,G) => call(G). ?-freeze(X,writeln(X)),X=f(a). f(a) CICLOPS'06

Co-routining and concurrency Delay clauses • Delay clausedelay and(X,Y,Z) if var(X),var(Y),X\==Y,Z\==1 • ARand(X,Y,Z), var(X),var(Y),X\==Y,Z\==1, {ins(X),ins(Y),ins(Z)} => true. CICLOPS'06

Co-routining and concurrencyCompiling flat GHC • Flat GHC • AR append([],Ys,Zs):-true | Ys=Zs. append([X|Xs],Ys,Zs):-true | Zs=[X|Zs1], append(Xs,Ys,Zs1). append(Xs,Ys,Zs),var(Xs),{ins(Xs)} => true. append([],Ys,Zs) => Ys=Zs. append([X|Xs],Ys,Zs) => Zs=[X|Zs1], append(Xs,Ys,Zs1). CICLOPS'06

Events for programming constraint propagation • generated: When suspended for the first time • ins(X): X is instantiated • bound(X) • A bound of X’s domain is updated • dom(X,E) • An inner value E is excluded from X’s domain • dom(X) • Some inner value is excluded from X’s domain • dom_any(X,E) • An arbitrary value E is excluded from X’s domain • dom_any(X) • Some value is excluded from X’s domain CICLOPS'06

Posting events on domain variables • X#\=2 • Posts dom(X,2) and dom_any(X,2) • X#\=4 • Posts bound(X) and dom_any(X,4) • X#\=1 • Posts ins(X) X :: 1..4, X#\=2, X#\=4, X#\=1. CICLOPS'06

Propagators for aX=bY+c • Forward checking 'aX=bY+c_forward'(A,X,B,Y,C),var(X),var(Y), {ins(X),ins(Y)} => true. 'aX=bY+c_forward'(A,X,B,Y,C),var(X) => T is B*Y+C, X is T//A, A*X=:=T. 'aX=bY+c_forward'(A,X,B,Y,C) => T is A*X-C, Y is T//B, B*Y=:=T. When either X or Y is instantiated, instantiate the other variable. CICLOPS'06

Propagators for aX=bY+c • Interval consistency 'aX in bY+c_interval'(A,X,B,Y,C),var(X),var(Y), {generated,bound(Y)} => 'aX in bY+c_reduce_domain'(A,X,B,Y,C). 'aX in bY+c_interval'(A,X,B,Y,C) => true. Whenever a bound of Y’s domain is updated, reduce X’s domain to achieve interval consistency. CICLOPS'06

Propagators for aX=bY+c • Arc consistency 'aX in bY+c_arc'(A,X,B,Y,C),var(X),var(Y), {dom(Y,Ey)} => T is B*Ey+C, Ex is T//A, (A*Ex=:=T -> X #\=Ex;true). 'aX in bY+c_arc'(A,X,B,Y,C) => true. Whenever an element Ey is excluded from Y’s domain, exclude Ey’s counterpart Ex from X’s domain. CICLOPS'06

Propagator for A1*X1+...+An*Xn+C = 0 'A1*X1+...+An*Xn+C=0'(C,A1,A2,...,An,X1,X2,..,Xn), n_vars_gt(n,2), {generated,ins(X1),bound(X1),...,ins(Xn),bound(Xn)} => reduce domains of X1,..,Xn to achieve ic. 'A1*X1+...+An*Xn+C=0'(C,A1,A2,...,An,X1,X2,..,Xn) => nary_to_binary(NewC,B1,B2,Y1,Y2), call_binary_propagator(NewC,B1,Y1,B2,Y2). When the constraint contains more than 2 variables, achieve interval consistency. When the constraint becomes binary archive arc consistency. CICLOPS'06

The use of the dom and dom_any events • The AC-4 algorithm for general support constraints • Channeling constraints in dual CSPs • Set constraints CICLOPS'06

The AC-4 algorithm for general support constraints ac4(BinaryRelation,X,Y), var(X),var(Y), {dom_any(X,Ex)} => decrement_counters(BinaryRelation,Ex,Y). ac4(BinaryRelation,X,Y) => true. • Whenever a value Ex is excluded from the domain of X,the counters of those values in the domain of Y supported by Ex are decremented. CICLOPS'06

Channeling constraints in dual CSPs • Dual CSPs • all_distinct([X1,…,XN]),Xi in 1..N • all_distinct([Y1,…,YN])Xi #= j #<=> Yj #= i Xi #\= j #<=> Yj #\= I • Relating primal and dual variables primal_dual(Xi,I,DualVarVector),var(Xi), {dom_any(Xi,J)} => arg(J,DualVarVector,Yj), Yj #\= I. primal_dual(Xi,I,DualVarVector) => true. CICLOPS'06

Set constraints • Representing finite-set domain variables using FD variables • Vl – The lower bound, complement of definite elements • Vu – The upper bound, possible elements • Vc – The cardinality • Example • V :: {1}..{1,2,3} • Vl :: [0,2..4] the complement of {1} including dummies • Vu :: [0..4] {1,2,3} including dummies • Vc :: [1..3] CICLOPS'06

Propagation for set constraints • Propagators for RS subset_from_R_to_S(set(Rl,_Ru,_Rc),S), {dom(Rl,E)} => clpset_add(S,E). subset_from_S_to_R(R,set(_Sl,Su,_Sc)), {dom(Su,E)} => clpset_exclude(R,E). CICLOPS'06

Benchmarking CLP(FD) systems(As of Aug. 14, 2006) CPU time, Windows XP Benchmarks: www.probp.com/bench.tar.gz BP: B-Prolog 6.9 EP: Eclipse 5.8 #107 GP: Gnu-Prolog 1.2.16 SP: Sicstus-Prolog 3.12.5 CICLOPS'06

Benchmarking CLP(FD) systems(Cont.) • Benchmarks:www.di.univaq.it/~formisano/CLPASP/www.probp.com/bench.tar.gz CPU time, Windows XP CICLOPS'06

Compiling CHR • A comparison of CHR and AR • Common features • Rule-based • Matching • Differences • Multi-headed rules are allowed in CHR • Implicit delay in CHR vs. explicit delay in AR CICLOPS'06

An example CHR program reflexivity @ leq(X,X) <=> true. antisymmetry @ leq(X,Y), leq(Y,X) <=> X = Y. idempotence @ leq(X,Y) \ leq(X,Y) <=> true. transitivity @ leq(X,Y), leq(Y,Z) ==> leq(X,Z). simplification simpagation propagation CICLOPS'06

Translating CHR into ARGeneral ideas • All rules are single or double-headed • When a constraint p(X) is added into the store, an event of the the following form is posted • For each occurrence of a constraint symbol and each matching constraint in the store, there is an agent watching the arrival of its partner constraint P <=> Body. P, Q <=> Body. P ==> Body. P \ Q <=> Body. P, Q ==> Body. constr(Cno,Alive,History,X) CICLOPS'06

Translating CHR into ARExample p(X),q(Y) <=> r(X,Y). p(X):- gen_constr_num(Cno), Constr=constr(Cno,AliveP,HistoryP,X), get_channel(p_1_1,ChP), get_channel(q_1_1,ChQ), agent_p_1_1(ChP,AliveP,X), post_p_1(ChQ,Constr,AliveP,X). agent_p_1_1(ChP,AliveP,X),var(AliveP), {event(ChP,Q),ins(AliveP)} => Q=constr(_,AliveQ,HistoryQ,Y), (var(AliveQ)->AliveP=0,AliveQ=0,r(X,Y);true). agent_p_1_1(ChP,AliveP,X) => true. CICLOPS'06

CHR to ARExample (Cont.) p(X),q(Y) <=> r(X,Y). post_p_1(ChQ,Constr,AliveP,X),var(AliveP), {generated,ins(X),ins(AliveP)} => post_event(ChQ,Constr). post_p_1(ChQ,Constr,AliveP,X) => true. CICLOPS'06

Benchmarking CHR compilers CPU time: milliseconds, Windows XP CICLOPS'06

CGLIB • Motivation • Implement an application with a GUI in one language • Features • Use constraints to specify the layouts of objects • Use action rules to specify interactions • Implementation • Implemented in B-Prolog, Java, JIPL, and C • Applications • Interactive user interfaces, animation, information visualization, intelligent agents, and games. CICLOPS'06

An example go:- cgButton(B,“Hello World!”), handleButtonClick(B), cgShow(B). handleButtonClick(B), {actionPerformed(B)} => halt. CICLOPS'06

actionPerformed(O) focusGained(O) focusLost(O) keyPressed(O,E) keyReleased(O,E) keyTyped(O,E ) mousePressed(O,E) mouseReleased(O,E) mouseEntered(O,E) mouseExited(O,E) mouseClicked(O,E) mouseDragged(O,E) mouseMoved(O,E) windowClosing(O) windowOpened(O) windowIconified(O) windowDeiconified(O) windowClosed(O) windowActivated(O) windowDeactivated(O) componentResized(O,E) componentMoved(O,E) textValueChanged(O) itemStateChanged(O,E) adjustmentValueChanged(O,E) time(T) Events for programming GUI CICLOPS'06

Timers and time events go:- timer(T1,100), timer(T2,1000), ping(T1), pong(T2), repeat,fail. ping(T),{time(T)} => writeln(ping). pong(T),{time(T)} => writeln(pong). CICLOPS'06

Demo of CGLIB • Graphical user interfaces • Animation • Information visualization • Constraint satisfaction problems • Games CICLOPS'06

The implementation of AR(The ATOAM architecture) registers code area X1 X2 ... Xn s P AR stack H heap T trail TOP CICLOPS'06

The frame structure for deterministic predicates • Frame slots • AR: Parent’s frame • CPS: Continuation PC • BTM: Bottom of the stack frame • TOP: Top of the stack Arguments AR CPS BTM TOP Local vars CICLOPS'06

The frame structure for agents(Suspension frames) Arguments AR CPS BTM TOP PREV STATE REEP EVENT Local vars • Frame slots • PREV: Previous suspension frame • STATE: State of the frame (start, sleep, woken, end) • REEP: Reentrance program pointer • EVENT: Activating event CICLOPS'06

The frame structure for non-deterministic predicates Arguments AR CPS BTM TOP B CPF H T SF Local vars • Frame slots • B: Parent choice point frame • CPF: Continuation PC on failure • H: Top of the heap • T: Top of the trail stack • SF: Suspension frame CICLOPS'06

Spaghetti stack • Context switching is light • Activation frames are not in chronological order • Run-time testing is needed to de-allocate a frame • The BTM slot is needed for de-allocation of frames • Stack needs be garbage collected CICLOPS'06

Conclusion • Conclusion • AR is a simple but powerful language which has a variety of applications • Further work • Multi-threaded AR • Even faster implementation • Debugging • Fast implementation of AR on WAM [B. Demoen] • New applications (Multi-agents) • More information • www.probp.com • www.bprolog.com CICLOPS'06

AR (Action Rules) The Language, Implementation, and Applications A tutorial given at CICLOPS’06