About Prolog

1. About Prolog Lu Han Written at 2007-08 Modified at 2008-02

2. Index • Part 1. Prolog Quick Tutorial • Part 2. Amzi! Prolog Overview • Part 3. Programming Interface （for C & C++）

3. Part 1. Prolog Quick Tutorial • What is Prolog？ • Prolog stands for PROgramming in LOGic • Prolog is based on First Order Predict Logic. • Prolog is declarative rather than procedural.

4. Part 1. Prolog Quick Tutorial • Logic Programming • Sample 1. • In classical logic we might say "All people are mortal," or, rephrased for Prolog, "For all X, X is mortal if X is a person." • mortal(X) :- person(X).

5. Part 1. Prolog Quick Tutorial • Similarly, we can assert the simple fact that Socrates is a person. • person(socrates). • From these two logical assertions, Prolog can now prove whether or not Socrates is mortal. • ?- mortal(socrates). • The listener responds • yes

6. Part 1. Prolog Quick Tutorial • First Order Predicate Logic（FOPL） • First order predicate logic implies the existence of a set of predicate symbols along with a set of connectives. • First order predicate logic implies that there is no means provided for “talking about” the predicates themselves. • Sample 2.

7. Part 1. Prolog Quick Tutorial • Procedural programming requires that the programmer tell the computer what to do. That is, how to get the output for the given inputs. • Declarative programming requires a more descriptive style. The programmer must know what relationships hold between various entities.

8. Part 1. Prolog Quick Tutorial • Prolog Constants • A constant is an atom or a number. • Atom include: • Quoted item • Word（lower case letter followed by any letter，digit or _） • Symbol （+, -, *, /, ^……） • Special item（[], {}, ;, !, %） • A number is an integer or a real number. • Sample 3. a, b_1, ‘Hello’, ‘常识组’, 2008, 3.14

9. Part 1. Prolog Quick Tutorial • The Logical Variables • A logical variable is a name starting with a capital letter or a single _. • Sample 4. X, Person, _

10. Part 1. Prolog Quick Tutorial • Predicates • Predicate means the relation or the property of a number of entities. • All predicate names must be constants, but not numbers. • No predicate may be a variable. • Prolog use /num to indicate the number of arguments • Sample 5. • likes(bill,ice_cream) —— right. likes/2

11. Part 1. Prolog Quick Tutorial • Clauses • A clause is the syntactic entity expressing a relationship. • A clause must terminate with a ‘.’ • Sample 6. • loves(jane,jim)—— a goal • loves(jane,jim).—— a clause

12. Part 1. Prolog Quick Tutorial • Multiple Clauses • A predicate may be defined by a set of clauses with the same predicate name and the same number of arguments. • Sample 7. • The logical statement • large_than(2,1) ∧large_than(3,2) • Prolog clauses • large_than(2,1). • large_than(3,2).

13. Part 1. Prolog Quick Tutorial • Facts • A fact is a unit clause. • Sample 8 • likes(bill,cake). • even(2).

14. Part 1. Prolog Quick Tutorial • Rule • A rule is a non-unit clause. • A rule consists of two parts: the head and the body. • No more than one goal is allowed in the head. • The head and the body are connected with “:-”. • The semantics of goal(X) :- p(X).is for all X, p(X)  goal(X) • Sample 9. father(X, Y) :- son(Y, X).

15. Part 1. Prolog Quick Tutorial • Conjunctions • Prolog uses ‘,’ to indicate the conjunction, which equivalent to the ∧ of predicate calculus. • Sample 10. • happy(Person) :- rich(Person), healthy(Person). • The rule means a person is happy if he/she is rich and healthy.

16. Part 1. Prolog Quick Tutorial • Disjunctions • Prolog uses ‘;’ to indicate the conjunction, which equivalent to the ∨ of predicate calculus. • Sample 11. • happy(Person) :- rich(Person); healthy(Person). • Or • happy(Person) :- rich(Person). • happy(Person) :- healthy(Person). • The rule means a person is happy if he/she is rich or healthy.

17. Part 1. Prolog Quick Tutorial • Recursion in rule • ancestor(P, A) :- ancestor(P, X), ancestor(X, A).—— Wrong! • This rule should be written as follow. • ancestor(P, A) :- parent(P, A). • ancestor(P, A) :- parent(P, P1), ancestor(P1, A).

18. Part 1. Prolog Quick Tutorial • Search Strategy • Prolog adopts depth first search as its search strategy. • A query is a goal which is submitted to Prolog in order to determine whether this goal is true or false. • Prolog uses the prompt ‘?-’ to expect the input queries.

19. Part 1. Prolog Quick Tutorial • Unifications • The predicate names and arities must be the same for unification to succeed. • Sample 12 • man(bill). • woman(jean). • ?-woman(jean). • yes —— unify with woman(jean) • ?-women(mary). • no —— a failed match

20. Part 1. Prolog Quick Tutorial • Subgoals • A top level goal can be divided into several subgoals. • Sample 13 • woman(jean). • man(fred). • wealthy(fred). • happy(Person) :- woman(Person), wealthy(Person). • ?-happy(jean). • no

21. Part 1. Prolog Quick Tutorial • happy(jean) :- woman(jean), wealthy(jean). • Then there are two subgoals, • woman(jean) • wealthy(jean) • Prolog solves the two subgoals in order. • The former subgoal is successful. • But we cannot unify wealthy(fred) with wealthy(jean), so happy(jean) is failed.

22. Part 1. Prolog Quick Tutorial • Backtracking • When one goal failed, Prolog moves back (backtracking) to next goal. • Sample 14. • man(john). • woman(jean). • ?-woman(Person). • Person = jean

23. Part 1. Prolog Quick Tutorial • Predicates for control • true/0 —— always true • father(jim,fred). Is logically equivalent to • father(jim,fred) :- true. • fail/0 —— always false • live_forever(Person) :- fail. • repeat/0 —— redo • test :- repeat, write(test), fail.

24. Part 1. Prolog Quick Tutorial • Negation • Prolog uses predicate \+/1 to indicate not (equivalent to ┐) • The predicate \+/1 takes a Prolog goal as its argument. It will succeed when the goal fails. • Sample 15 • man(jim). • ?-\+man(jim). • no

25. Part 1. Prolog Quick Tutorial • \+/1 is not at all like logical negation. • \+(\+goal) is not identical to goal. • Sample 16 • man(jim). • woman(X) :- \+(man(X)). • ?-woman(jane). • yes • ?-woman(Person).//zsd 似乎所有的常量都代入成功才行。 • no

26. Part 1. Prolog Quick Tutorial • Using Negation in Case selection • Sample 17 • goal_1 :- odd(X). • goal_2 :- \+odd(X).

27. Part 1. Prolog Quick Tutorial • Condition • Prolog uses test-process to guarantee that some process will be done only when conditions are satisfied. • test_process(Cond, X, Y) :- test(Cond), process(Cond, X, Y).

28. Part 1. Prolog Quick Tutorial • Sample 18 • p(Person, Age) :- Age < 20, write(Person), write(‘ is young’); Age == 20, write(Person), write(‘ is 20’); Age >=60, write(Person), write(‘ is old’).

29. Part 1. Prolog Quick Tutorial • If _then_else • Prolog uses (test)->process1;process2 as if_then_else. • Sample 19 • P2(Person) :- (man(Person)-> write(Person), write(‘ is male’); write(Person), write(‘ is female’)).

30. Part 1. Prolog Quick Tutorial • Failure-Driven Loop//???zsd • The idea of failure-driven loop is deliberately generate a term and then fail. • failure_drivern_loop(Info) :- generate(Info,Term), fail. • failure_drivern_loop(Info).

31. Part 1. Prolog Quick Tutorial • Sample 20 • int(1). • int(2). • int(3). • print_int :- int(X), write(X), fail. • print_int. • ?-print_int. • 123 • yes

32. Part 2. Amzi! Prolog Overview • Amzi! Prolog consists of Amzi! Prolog and logic server. It is provided by Amzi! Inc. • www.amzi.com • Editions: Free, Personal/Student, Developer, Professional, Enterprise

33. Part 2. Amzi! Prolog Overview • Amzi! Prolog IDE

34. Part 2. Amzi! Prolog Overview • New a Project • File -> new -> Project…-> Prolog project -> Project name -> Create a new Prolog project • New a File • File -> new -> File -> Direction select -> File name(*.pro) -> Create a new file

35. Part 2. Amzi! Prolog Overview • Document composition • Logical Layer —— rule files • Data Layer —— fact files • Control layer —— main function, input/output etc.

36. Part 2. Amzi! Prolog Overview • Debug • Run -> Debug As… • Run • Run -> Run As -> • 1 Compiled Project (xpl) • 2 Interpreted Project (pro) • 3 Interpreted Single File (pro)

37. Part 2. Amzi! Prolog Overview • Listener • The Prolog listener is an interactive environment that allows a programmer to query any part of the Prolog logic base, or program.

38. Part 2. Amzi! Prolog Overview • Adding and Removing Clauses • Assert can be used to directly add clauses. • ?- assert( likes(ella, crackers) ). • yes • Retractall ca be used to remove clauses. • ?-retractall( likes(ella, crackers) ). • yes

39. Part 2. Amzi! Prolog Overview • The listener attempts to prove the goal, returning values of any variables. You can then enter: • ; - request backtracking to look for more answers. • Enter key - to return to the listener prompt.

40. Part 2. Amzi! Prolog Overview • Consulting Prolog Source Files • consult(File) - the specified file is consulted. If no extension is provided, then '.pro' is assumed. • consult( [File1, File2, ..., FileN] ) - consults each of the files in the list.

41. Part 2. Amzi! Prolog Overview • Listing Clauses • The listing predicate displays a listing of your clauses. • ?-listing. • Exits the current listener. • ?-quit.

42. Part 3. Programming Interface • Install Amzi Prolog Inference Engine (PIE) in your machine. • Include amzi.h and logicserver.h in your VC project. (..\amzi\amzi_7-6-6\include\) • Include amzi.lib in your VC project. (..\amzi\amzi_7-6-6\lib\) • Project -> settings… -> Link -> Object/library modules -> add amzi.lib

43. Part 3. Programming Interface • Include prolog.h (my VC Interface Class)in your VC project. • class Prolog • Prolog( string filename ); • void Load( string filename); • void Assert( string str ); • void Retract( string filename); • VSTR Prolog::Call( string command ); • VSTR GetPar( string command, int n_Par);

44. Part 3. Programming Interface • Generate .xpl in your PIE. • Run -> Run As… -> 1 Compiled Project (xpl) • Copy the xpl file to your VC project. • Call Prolog via class Prolog. • Run your project.

45. Part 3. Programming Interface • Another way for call Prolog • main.xpl • cmd -> main Rule, Data, Query, Output

46. Thank You! Question and discussion are welcome.