1 / 48

Introduction to Prolog: Logic Programming Basics

Explore Prolog language elements, facts, rules, and executing Prolog queries. Learn about variables, compound terms, and Prolog predicates. See examples of facts and rules in action.

brandy
Télécharger la présentation

Introduction to Prolog: Logic Programming Basics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Computer Engineering Lab II 242-203, Semester 2, 2013-2014 Please ask questions Introduction to Prolog Who I am: Andrew DavisonWiG Lab Officead@fivedots.coe.psu.ac.th 242-203 Comp. Eng. II: Intro. to Prolog

  2. Outline • 7. The append/3 Predicate • 8. Other List Predicates • 9. The not/1 Predicate • 10. Using Strawberry Prolog • 11. More Information • 1. Language Elements • 2. Executing Prolog • 3. Rules • 4. Recursive Rules • 5. Operators • 6. Lists 241-203 Software Lab II: Intro. to Prolog

  3. 0. Why Prolog? • Very popular in Artificial Intelligence (AI) • Unique features include: • unification (more powerful assignment) • backtracking • close links to predicate logic • Very different from C, Java • an engineer must know more than 1 tool • Prolog is a logic programming language 241-203 Comp Eng Lab II: Intro. to Prolog

  4. C Program Compared to Prolog • void foo(...){ ... }int bar(...){ ... }void main(){ ... } • Prolog predicate-- made up of facts and rulesProlog predicate -- more facts and rules?- Prolog query. Data types: term, list Lots of data types: int, char, struct, pointer, ... 241-203 Comp Eng Lab II: Intro. to Prolog

  5. 1. Language Elements • Terms • Facts and Rules • they use terms as data structures • Predicates • made up of facts and rules • The (Logic) Program • made up of predicates 241-203 Software Lab II: Intro. to Prolog

  6. Terms Terms are data. • Constants adam paris 5 3.14 [] ´Adam’ ... • Variables X Y List _12 _ ... • Compound terms (something like structs) plus(2,3) foo(2,bar(a,'Jim')) ... 2+3 // infix notation 241-203 Software Lab II: Intro. to Prolog

  7. Facts • A fact has the form p(t1,...,tn). • p is the name of the fact • t1, …, tn are term arguments of the fact • Examples: edge(a, X).parent(adam, bill). note the '.'s 241-203 Software Lab II: Intro. to Prolog

  8. Example parent(kim,holly).parent(margaret,kim).parent(margaret,kent).parent(esther,margaret).parent(herbert,margaret).parent(herbert,jean). • Six facts about families: • kim is the parent of holly • Defines a predicateparent of arity 2 • parent/2 for short note the '.'s 241-203 Software Lab II: Intro. to Prolog

  9. Facts are not Terms • A fact : parent(kim, holly).is part of the program. • A term: foo(1, 4)is a piece of data used inside a fact (or rule). 241-203 Software Lab II: Intro. to Prolog

  10. Facts using Term Data • A staff/2 predicate: staff( name(andrew), room(101) ).staff( name(mondri), room(403) ).staff( name(chatchai), room(301) ). • Each staff/2 fact uses two terms. 241-203 Software Lab II: Intro. to Prolog

  11. 2. Executing Prolog more details in section 10

  12. Use a query to execute Prolog code. • In SB Prolog: • execute query, print results with write()s • use F5 (or Run|Run) to execute the query • the output appears in the Output window. 241-203 Software Lab II: Intro. to Prolog

  13. Simple Queries • The queries: ?- parent(margaret, kent). Yes // printed in the Output window ?- parent(fred, pebbles). No 241-203 Software Lab II: Intro. to Prolog

  14. Queries With Variables • Query: ?- parent(P, jean), write(P), write("\n") herbertYes ?- parent(P, esther), write(P), write("\n") No • In SB Prolog, the variable bindings must be printed by the query. 241-203 Software Lab II: Intro. to Prolog

  15. Flexibility • Variables can appear anywhere in a query: ?- parent(Parent,jean). ?- parent(esther,Child). ?- parent(Parent,Child). ?- parent(Person,Person). 241-203 Software Lab II: Intro. to Prolog

  16. Conjunctions note the ',' ?- parent(margaret,X), parent(X,holly), write(X), write("\n"). kim Yes • A conjunction is a series of queries. • The Prolog system tries to prove them all by making variable bindings • e.g. bind X to kim 241-203 Software Lab II: Intro. to Prolog

  17. Multiple Solutions the user types 'F8' to make SB Prolog look for another answer

  18. 3. Rules head greatgrandparent(GGP,GGC) :- parent(GGP,GP), parent(GP,P), parent(P,GGC). • To prove the head, prove the conditions. • To prove greatgrandparent(GGP,GGC), find some GP and P for which you can prove parent(GGP,GP), then parent(GP,P), and finally parent(P,GGC). conditions 241-203 Software Lab II: Intro. to Prolog

  19. A Program With a Rule parent(kim,holly).parent(margaret,kim).parent(margaret,kent).parent(esther,margaret).parent(herbert,margaret).parent(herbert,jean).greatgrandparent(GGP,GGC) :- parent(GGP,GP), parent(GP,P), parent(P,GGC). • parent/2 and greatgrandparent/2 predicates. 241-203 Software Lab II: Intro. to Prolog

  20. parent/2 as a Graph herbert esther parent jean margaret kim kent holly 241-203 Software Lab II: Intro. to Prolog

  21. Example • This shows the initial query and final result. • There are intermediate goals inside the system: ?- greatgrandparent(esther,GreatGrandchild), write(GreatGrandchild), write("\n"). hollyYes 241-203 Software Lab II: Intro. to Prolog continued

  22. 1. parent(kim,holly).2. parent(margaret,kim).3. parent(margaret,kent).4. parent(esther,margaret).5. parent(herbert,margaret).6. parent(herbert,jean).7. greatgrandparent(GGP,GGC) :- parent(GGP,GP), parent(GP,P), parent(P,GGC). greatgrandparent(esther,GreatGrandchild) Clause 7, binding GGP to esther and GGC to GreatGrandChild parent(esther,GP), parent(GP,P), parent(P,GreatGrandchild) Clause 4, binding GP to margaret parent(margaret,P), parent(P,GreatGrandchild) Clause 2, binding P to kim parent(kim,GreatGrandchild) Clause 1, binding GreatGrandchild to holly 241-203 Software Lab II: Intro. to Prolog

  23. Rules Using Other Rules • Note that both rules use a variable P. • The scope of the definition of a variable is the fact/rule that contains it. greatgrandparent(GGP,GGC) :- grandparent(GGP,P), parent(P,GGC).grandparent(GP,GC) :- parent(GP,P), parent(P,GC). 241-203 Software Lab II: Intro. to Prolog

  24. 4. Recursive Rules ancestor(X,Y) :- parent(X,Y).ancestor(X,Y) :- parent(Z,Y), ancestor(X,Z). • X is an ancestor of Y if: • Base case: X is a parent of Y • Recursive case: there is some Z such that Z is a parent of Y, and X is an ancestor of Z • Prolog tries rules in the order you give them, so put base-case rules and facts first. 241-203 Software Lab II: Intro. to Prolog

  25. parent/2 again herbert esther parent(kim,holly).parent(margaret,kim).parent(margaret,kent).parent(esther,margaret).parent(herbert,margaret).parent(herbert,jean). jean margaret kim kent holly 241-203 Software Lab II: Intro. to Prolog

  26. ancestor/2 Queries ?- ancestor(kim,holly).Yes ?- ancestor(A,holly), write(A), write("\n").kimmargaret // I typed F8esther // typed F8herbert // typed F8No // typed F8 241-203 Software Lab II: Intro. to Prolog

  27. 5. Operators • Prolog systems have many built-in operators. e.g. =/2 is/2 and arithmetic 241-203 Software Lab II: Intro. to Prolog

  28. The =/2 Predicate • The goal =(X,Y) succeeds if Xand Y can be unified • "unify" means create variable bindings • Usually written as X = Y ?- name(adam,seth) = name(adam,X), write(X), write("\n").seth Yes 241-203 Software Lab II: Intro. to Prolog

  29. Arithmetic Operators • Terms +, -, * and / are operators, with the usual precedence and associativity ?- X = +(1,*(2,3)).X = 1+2*3 ?- X = 1+2*3.X = 1+2*3 No evaluation yet. 241-203 Software Lab II: Intro. to Prolog

  30. Evaluating Arithmetic • The general format is: Variable is operation_term ?- X is 1+2*3, write(X), write("\n").7 yes 241-203 Software Lab II: Intro. to Prolog

  31. List notation Meaning [] an empty list [1] list with 1 value [1,2,3] 3 value list [1,name(X,Y)] 2 value list 6. Lists 241-203 Software Lab II: Intro. to Prolog

  32. Examples ?- X = [1, 2, 3].X = [1, 2, 3] ?- [X, Y, Z] = [1, 2, 3].X = 1Y = 2Z = 3 241-203 Software Lab II: Intro. to Prolog

  33. List Notation With Tail • [1,2|X] unifies with a list that starts with 1,2 and binds X to the tail. ?- [1,2|X] = [1,2,3,4,5].X = [3, 4, 5] 241-203 Software Lab II: Intro. to Prolog

  34. 7. The append/3 Predicate • append(X,Y,Z) succeeds when Z is the same as the list Y appended onto the end of the list X. append([], B, B).append([Head|TailA], B, [Head|TailC]) :- append(TailA, B, TailC). ?- append([1,2],[3,4],Z), write(Z), write("\n").[1, 2, 3, 4] Yes 241-203 Software Lab II: Intro. to Prolog

  35. Other Uses of append/3 • append/3 can be called with variables in any of its argument positions. ?- append(X,[3,4],[1,2,3,4]), write(X), write("\n").[1, 2] Yes 241-203 Software Lab II: Intro. to Prolog

  36. Multiple Answers ?- append(X,Y,[1,2,3]).X = []Y = [1, 2, 3]X = [1]Y = [2, 3]X = [1, 2]Y = [3]X = [1, 2, 3]Y = []No By using F8 241-203 Software Lab II: Intro. to Prolog

  37. In SB Prolog: writeBind(Str, Val) :- write(Str), write(" = "), write(Val), write("\n"). ?- append(X, Y,[1,2,3]), writeBind("X", X), writeBind("Y", Y). 241-203 Software Lab II: Intro. to Prolog

  38. Predicate Description member(X,Y) Succeeds if X is an element in the list Y. length(X,Y) Succeeds if the list X is length Y. 8. Other List Predicates • Flexible, like append/3 • queries can contain variables anywhere. 241-203 Software Lab II: Intro. to Prolog

  39. member/2 member(X, [X|_]). member(X, [Y|Rest]) :- member(X, Rest). • member(X,L) succeeds if X is an element in the list L ?- member(1,[1,2,3]).yes?- member(a,[a,n,d,y]).yes ?- member(X,[j,i,m]), write(X), write("\n").ji // F8m // F8no // F8 241-203 Software Lab II: Intro. to Prolog

  40. length/2 length([], 0). length([X|Rest], Len) :- length(Rest, LenRest), Len is LenRest + 1. • length(X,Y) succeeds if Y is the length of the list X. ?- length([a,b,c,d], L), write(L), write("\n").4?- length([1,2,3], 4).no 241-203 Software Lab II: Intro. to Prolog

  41. 9. The not/1 Predicate ?- not( member(4,[1,2,3]) ).Yes ?- not( member(1,[1,2,3]) ).No • Built-in not(X) succeeds when X fails. • Only use not/1 when its goal contains no variables. (Use not/1 only as a test.) 241-203 Software Lab II: Intro. to Prolog

  42. 10. Using Strawberry Prolog • Download the installation program for the SB Prolog system from: http://fivedots.coe.psu.ac.th/ Software.coe/LAB/Prolog/ • The filename: Strawberry Prolog 2.92 for Vista/XP • Read the readme.txt file in the same directory. It's for Win 7 too. 241-203 Software Lab II: Intro. to Prolog

  43. Start SB Prolog from C:\Program Files\Strawberry Prolog\Prolog.exe:

  44. Create a Prolog Program using any text editor saved in c:/windows/desktop/parents.pro 241-203 Software Lab II: Intro. to Prolog

  45. Alternatively, you can just type into a new Prolog file window, then save at the end. • in SB Prolog select File|New, and choose "Prolog File" • at the end, select File|Save 241-203 Software Lab II: Intro. to Prolog

  46. Running parents.pro • Load the file using the menu item File|Open. • Type in a query into the parents.pro window: • ?- parent(X, Y), write(X), write(" and "), write(Y). • Select Run|Run from the menu • Check the Output window 241-203 Software Lab II: Intro. to Prolog

  47. 11. More Information • The Help menu in the SB Prolog system leads to: • a tutorial • a Prolog language guide • examples 241-203 Software Lab II: Intro. to Prolog continued

  48. SB Prolog’s Web Site: • http://www.dobrev.com/light.html • v.2.92, and other versions • A complete Prolog book (in PDF format): • http://www.ida.liu.se/~ulfni/lpp/ • Online Prolog tutorials list at • http://www.thefreecountry.com/documentation/ onlineprolog.shtml 241-203 Software Lab II: Intro. to Prolog

More Related