![Syntax of Prolog: Lists as special terms
🞂 Lists are a very useful data structure in Prolog.
🞂 Lists are structured terms represented in a special way.
🞂 [a,b,c,d]
🞂 This is actually the structured term
[a | [c | [b | [d | []]]]]
🞂 Where [] is a special constant the empty list.
🞂 Each list is thus of the form [<head> | <rest_of_list>]
🞂 <head> an element of the list.
🞂 <rest_of_list> is a list (a sub-list).
🞂 also, [a,b,c,d]=[a|[b,c,d]] =[a,b|[c,d]] = [a,b,c|[d]]
🞂 List elements can be any term! For example the list [a, f(a), 2, 3+5,
point(X,1.5,Z)] contains 5 elements.](https://image.slidesharecdn.com/prolog-241118105306-0c683025/85/Prolog-language-programming-in-the-facts-pptx-23-320.jpg)
Prolog language programming in the facts.pptx
- 1. SWI-Prolog
- 3. https://www.swi-prolog.org/download/stable SWI-Prolog has been under continuous development since 1987. Its main author is Jan Wielemaker. The name SWI is derived from Sociaal- Wetenschappelijke Informatica ("Social Science Informatics"), the former name of the group at the University of Amsterdam, where Wielemaker is employed. sudo apt-add-repository ppa:swi-prolog/stable sudo apt-get update sudo apt-get install swi-prolog
- 4. What is Prolog? Prolog or PROgramming in LOGics is a logical and declarative programming language. It is one major example of the fourth generation language that supports the declarative programming paradigm. This is particularly suitable for programs that involve symbolic or non-numeric computation. This is the main reason to use Prolog as the programming language in Artificial Intelligence, where symbol manipulation and inference manipulation are the fundamental tasks. In Prolog, we need not mention the way how one problem can be solved, we just need to mention what the problem is, so that Prolog automatically solves it. However, in Prolog we are supposed to give clues as the solution method. Prolog language basically has three different elements − Facts The fact is predicate that is true, for example, if we say, “Tom is the son of Jack”, then this is − a fact. Rules Rules are extinctions of facts that contain conditional clauses. To satisfy a rule these − conditions should be met. For example, if we define a rule as − grandfather(X, Y) :- father(X, Z), parent(Z, Y) This implies that for X to be the grandfather of Y, Z should be a parent of Y and X should be father of Z. Questions And to run a prolog program, we need some questions, and those questions can be −
- 5. Open source software • Open source software is software that can be freely used, changed, and shared (in modified or unmodified form) by anyone.
- 6. SWI-Prolog •SWI-Prolog offers a comprehensive FREE SOFTWARE • Prolog environment. Link for downloading: •http://www.swi-prolog.org/download/stable •A Self-installing executable for MS-Windows: swipl- win.exe •Works on Windows •LINUX versions are also available.
- 7. Introduction-PROLOG • PROgramming in LOGic FACTS RULES CONCLUSIONS
- 8. • Olivia likes Pizza. likes(olivia, pizza). FACTS OBJECTS RELATIONSHIP Introduction-PROLOG OBJECTS FACTS RELATIONSHIP
- 9. • Olivia is student. student(olivia). FACTS OBJECTS RELATIONSHIP Introduction-PROLOG OBJECT FACT RELATIONSHIP • Beginning with lower case letters. • End the fact with period (full stop).
- 10. Basic Constructs of Prolog progarm
- 11. Knowledge Base Introduction-PROLOG PROLOG programming is all about writing knowledge base Clauses
- 12. } Facts are statements about what is true about a problem, instead of instructions how to accomplish the solution. } The Prolog system uses the facts to work out how to accomplish the solution by searching through the space of possible solutions. } It is defined by an identifier followed by an n-tuple of constants. } A relation identifier is referred to as a predicate } When a tuple of values is in a relation we say the tuple satisfies the predicate.
- 13. } Names of relationship and objects must begin with a lower- case letter. } Relationship is written first (typically the predicate of the sentence). } Objects are written separated by commas and are enclosed by a pair of round brackets. } The full stop character ‘.’ must come at the end of a fact.
- 14. •Predicate •valuable(gold) owns(john,gold) father(john,mary) •gives (john,book,mary) Interpretation Gold is valuable. John owns gold. John is the father of Mary John gives the book to Mary Examples
- 15. } Specifies under what conditions a tuple of values satisfies a predicate. } The basic building block of a rule is called an atom } Atom :- Atom1, ..., Atomn If each of Atom1,...,Atomn is true, then Atom is also true.
- 16. Knowledge base • General Rule: –If the body of the rule is true then head implies true • Clauses: 5 • Predicates 3
- 17. • ?- author(khalid). • What is result of the query? – True
- 18. Example 1 : Below food table shows the facts, rules, goals and their English meanings . Facts English meanings food(burger). // burger is a food food(sandwich). // sandwich is a food food(pizza). // pizza is a food lunch(sandwich). // sandwich is a lunch dinner(pizza). // pizza is a dinner Rules meal(X) :- food(X). // Every food is a meal OR Anything is a meal if it is a food Queries / Goals ?- food(pizza). // Is pizza a food? ?- meal(X), lunch(X). //Which food is meal and lunch? ?- dinner(sandwich). // Is sandwich a dinner?
- 19. • From Example 1 : (1) ?- meal(X), dinner(X). (2) ?- meal(What). (3) ?- meal(X), dinner(Y).
- 20. Syntax of Prolog: Terms ⮚ Constants: Identifiers 🞂 sequences of letters, digits, or underscore “_” that start with lower case letters. 🞂 mary, anna, x25, x_25, alpha_beta 🞂 Numbers 🞂 1.001, 2, 3.03 🞂 Strings enclosed in single quotes 🞂 'Mary', '1.01‘, ‘string' ◻ Note can start with upper case letter, or can be a number now treated as a string. ⮚ Variables 🞂 Sequence of letters digits or underscore that start with an upper case letter or the underscore. 🞂 _x, Anna, Successor_State,
- 21. Syntax of Prolog: Terms 🞂 Constants: 🞂 Variables 🞂 Structures (like function applications) 🞂 <identifier>(Term1, ..., Termk) 🞂 date(1, may, 1983) 🞂 point(X, Y, Z) 🞂 Note that the definition is recursive. So each term can itself be a structure 🞂 date(+(0,1), may, +(1900,-(183,100))) 🞂 Structures can be represented as a tree
- 22. Syntax of Prolog: Terms 🞂 Structures as trees 🞂 date(+(0,1), may, +(1900,-(183,100))) + may + 0 1 1900 + 0 1 date
- 23. Syntax of Prolog: Lists as special terms 🞂 Lists are a very useful data structure in Prolog. 🞂 Lists are structured terms represented in a special way. 🞂 [a,b,c,d] 🞂 This is actually the structured term [a | [c | [b | [d | []]]]] 🞂 Where [] is a special constant the empty list. 🞂 Each list is thus of the form [<head> | <rest_of_list>] 🞂 <head> an element of the list. 🞂 <rest_of_list> is a list (a sub-list). 🞂 also, [a,b,c,d]=[a|[b,c,d]] =[a,b|[c,d]] = [a,b,c|[d]] 🞂 List elements can be any term! For example the list [a, f(a), 2, 3+5, point(X,1.5,Z)] contains 5 elements.
- 24. Syntax of Prolog: Predicates 🞂 Predicates are syntactically identical to structured terms <identifier>(Term1, ..., Termk) 🞂 elephant(mary) 🞂 taller_than(john, fred)
- 25. True (if they unify) ?-X = Y False (otherwise) built in Rules:- i) X and Y are permitted to be uninstantiated variables. ii) Integers and atoms are always equal to themselves. iii) 2 structures are equal only if :- a) Same functions. b) No. of components. c) corresponding components are equal. Eg. a(b,c(d,e))= a(X, c(Y, e)) X = b Y = d X = Y Y = 10 X= 10
- 27. Operation 🞂 p(1) :- a(1). p(1) :- b(1). a(1) :- c(1). c(1) :- d(1). c(1) :- d(2). b(1) :- e(1). 🞂 Backtracking can occur at every stage as the query is processed. p(1) a(1) c(1) b(1) e(1) d(3) e(1). d(3). Query: d(1) d(2) p(1) 27
- 28. Operation 🞂 With backtracking we can get more answers by using “;” 🞂 p(1) :- a(1). p(1) :- b(1). a(1) :- c(1). c(1) :- d(1). c(1) :- d(2). b(1) :- e(1). b(1) :- d(3). p(1) a(1) c(1) b(1) e(1) e(1). d(3). Query: d(1) d(2) p(1) d(3) 28
- 30. • Prolog uses two types of comments: • Line comments go from the “%” symbol to the end of the line – % This is a comment AAn Introduction to Prolog • Multiline comments begin with a “/*” and end with a “*/” – /* this is a comment */