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![19
Lists and Sequence in Prolog
In Prolog, the list builder uses brackets[...]. A list is referred by the
notation [A | B] in which, A is the first element, and whose tail is B.
The following example shows the three definitions, where the first
element of the list is refereed by the 'car', the tail of the list is referred
by 'cdr', list constructor is referred by the 'cons'.
car([A | B], A).
cdr([A | B], B).
cons[A, B, [A | S]).
Where,
•A is the head(car) of [A | B].
•B is the tail(car) of [A | B].
•Put A at the head and B as the tail constructs the list [A | S].
The predicate 'member/2' definition is described as follows:
member(A, [A | S]).
member(A, [B | S]) :- member(A, S).
The clauses can be read as follows:
•A is a list member whose first element is A.
•A is a list member whose tail is S if A is a member of S.](https://image.slidesharecdn.com/prologprologprogramming-220707084233-463acf8a/85/Prolog-Prolog-Programming-IN-AI-pdf-17-320.jpg)
![19
Lists and Sequence in Prolog
In Prolog, the list builder uses brackets[...]. A list is referred by the
notation [A | B] in which, A is the first element, and whose tail is B.
The following example shows the three definitions, where the first
element of the list is refereed by the 'car', the tail of the list is referred
by 'cdr', list constructor is referred by the 'cons'.
car([A | B], A).
cdr([A | B], B).
cons[A, B, [A | S]).
Where,
•A is the head(car) of [A | B].
•B is the tail(car) of [A | B].
•Put A at the head and B as the tail constructs the list [A | S].
The predicate 'member/2' definition is described as follows:
member(A, [A | S]).
member(A, [B | S]) :- member(A, S).
The clauses can be read as follows:
•A is a list member whose first element is A.
•A is a list member whose tail is S if A is a member of S.](https://image.slidesharecdn.com/prologprologprogramming-220707084233-463acf8a/75/Prolog-Prolog-Programming-IN-AI-pdf-17-2048.jpg)
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- 1.
- 2. Introduction Prolog Prolog is alogic programming language. It has important role in artificial intelligence. Unlike many other programming languages, Prolog is intended primarily as a declarative programming language. In prolog, logic is expressed as relations (called as Facts and Rules). Core heart of prolog lies at the logic being applied. Formulation or Computation is carried out by running a query over these relations. 4 Prolog
- 3. Prolog program issimply based on predicate logic known as Horn clause. In prolog, we compose the program using facts and rules and we pose a query on query prompt about the facts and rules we inserted. 5 Prolog Programming Basics Horn Clause : Horn clause consists of head (left hand side) and body (right hand side). Head can have 0 or 1 predicate and body can have list of predicates. That means LHS has only single literal and RHS can have more than one literals. head:- body.
- 4. What is Prolog? »Prolog or PROgramming in LOGics is a logical and declarative programming language. It is one major example of the fifth 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. 6
- 5. Programming languages areof two kinds: Procedural (BASIC, Fortran, C++, Pascal, Java); Declarative (LISP, Prolog, ML). In procedural programming, we tell the computer how to solve a problem. In declarative programming, we tell the computer what problem we want solved. SWI-Prolog offers a comprehensive free Prolog environment. Since its start in 1987, SWI-Prolog development has been driven by the needs of real world applications. SWI-Prolog is widely used in research and education as well as commercial applications. Prolog was originally designed to be an AI language, and it is very well suited for expert systems, planning systems and similar AI applications. Logic Programming: Prolog SWI - Prolog The logic programming language PROLOG (Programmation en Logique) was conceived by Alain Colmerauer at the University of Aix-Marseille, France, where the language was first implemented in 1973. PROLOG was further developed by the logician Robert Kowalski, a member of the AI group at the University of Edinburgh.
- 6. 8 Machine Logical Programming Machine Answer Int main() { Procedure1 () Procedure 2 () return } Knowledge Base Queries Functional Programming Prolog Interpreter Facts & Rules
- 7. Rules are extinctionsof facts that contain conditional clauses. To satisfy a rule these conditions should be met. Rules And to run a prolog program, we need some questions, and those questions can be answered by the given facts and rules Questions Facts are statements that describe object properties or relations between objects. The fact is predicate that is true, for example, if we say, “Tom is the son of Jack”, then this is a fact. Facts Prolog language basically has three different elements − Facts Rules Queries
- 8. Prolog Syntax The syntaxof Prolog is as follows: relationship(object1,object2)
- 9. Prolog » Example: » “Arslanowns the book” » Owns (arslan, book) relationship(object1, object2) » The relationship has a specific order, arslan own the book, but the book dose not owns arslan, and this relationship and its representation above called fact. 11
- 10. English Predicate CalculusProlog If → :- Not ~ Not Or V ; and ^ , female, Male, X, Y, mother_of, _father, Pro34 Variable is a string. The string can be a combination of lower case or upper case letters. The string can also contain underscore characters that begin with an underscore or an upper-case letter. Rules for forming names and predicate calculus are the same. Using the following truth-functional symbols, the Prolog expressions are comprised. These symbols have the same interpretation as in the predicate calculus. Symbols Variables
- 11. 13 A fact islike a predicate expression. It is used to provide a declarative statement about the problem. In a Prolog expression, when a variable occurs, it is assumed to be universally quantified. Facts are specified in the form of the head. Head is known as the clause head. It will take in the same way as the goal entered at the prompt by the user. Facts cat(momo). /* momo is a cat */ dog(pulu). /* pulu is a dog */ likes(arslan, jolie). /* Arslan likes Jolie*/ not(likes(Jolie, pasta)). /* Jolie does not like pasta */ For example: Queries In Prolog, the query is the action of asking the program about the information which is available within its database. When a Prolog program is loaded, we will get the query prompt, ?- 'It is sunny'. yes ?- ?- 'It is cold'. no ?- no ?- ?- ’momo is cat'. yes ?- ?- ’momo is dog'.
- 12. Rules extend thelogic program capabilities. Rules are used to provide the decision-making process in Prolog. Rules are specified in the form: head:- t1, t2, t3,….., tk. Where k>=1 The head is known as the clause of the head. :- is known as the clause neck. It is read as 'if'. The body of the clause is specified by t1, t2, t3,…, tk. It contains one or more components, and it can be separated using the commas. A rule will read as 'head is true if t1, t2, t3,…., tk are all true'. Rules In the following program, first two lines indicate the facts and last two lines indicate the rules: dog(pulu). large(pulu). cat(momo). large(momo). large_animal(A) :- dog(A),large(A). large_animal(C) :- cat(C),large(C). The above rules mean that 'large_animal(A) is true if dog(A) is true, and large(A) is true, etc.' The last line means that 'large_animal(C) is true if cat(C) is true, and large(C) is true. Facts and Rules make up the knowledge base.
- 13. likes(tarzan, jane). likes(jane, tarzan). likes(terk,jane). facts Arguments / objects / items .dot is necessary to end the statement relation friends(X,Y):- likes(X,Y), likes(Y,X). Predicate name head body variables Horn Clause
- 14. Example elephant(george). elephant(mary). elephant(X) :- grey(X),mammal(X), hasTrunk(X). Procedure for elephant Predicate Clauses Rule Facts ?- elephant(george). yes ?- elephant(jane). no Queries Replies
- 15. Queries Rules facts Example 1 :Below food table shows the facts, rules, goals and their English meanings. Queries / Goals ?- food(pizza). // Is pizza a food? ?- meal(X), lunch(X). // Which food is meal and lunch? ?- dinner(sandwich). // Is sandwich a dinner? 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 Rule meal(X) :- food(X). // Every food is a meal OR Anything is a meal if it is a food
- 16. Queries Rules facts Example 2 :Below student-professor relation table shows the facts, rules, goals and their English meanings. . Facts English meanings studies(charlie, csc135). // charlie studies csc135 studies(olivia, csc135). // olivia studies csc135 studies(jack, csc131). // jack studies csc131 studies(arthur, csc134). likes('John', car(bmw)) // arthur studies csc134 // Read as : john likes bmw car gives(john, chocolate, jane). // Read as : john gives chocolate to jane Rules professor(X, Y) :- teaches(X, C), studies(Y, C). // X is a professor of Y if X teaches C and Y studies C. Queries / Goals ?- studies(charlie, What). // charlie studies what? OR What does charlie study? ?- professor(kirke, Students). // Who are the students of professor kirke.
- 17. 19 Lists and Sequencein Prolog In Prolog, the list builder uses brackets[...]. A list is referred by the notation [A | B] in which, A is the first element, and whose tail is B. The following example shows the three definitions, where the first element of the list is refereed by the 'car', the tail of the list is referred by 'cdr', list constructor is referred by the 'cons'. car([A | B], A). cdr([A | B], B). cons[A, B, [A | S]). Where, •A is the head(car) of [A | B]. •B is the tail(car) of [A | B]. •Put A at the head and B as the tail constructs the list [A | S]. The predicate 'member/2' definition is described as follows: member(A, [A | S]). member(A, [B | S]) :- member(A, S). The clauses can be read as follows: •A is a list member whose first element is A. •A is a list member whose tail is S if A is a member of S.
- 18. The looping facilityis contained in most of the programming languages. Looping is used to enable a set of instructions to be repeatedly executed either a fixed number of times or until a given condition met. Prolog has no looping facility, but we can obtain a similar effect. Using this effect, we can evaluate a sequence of goals repeatedly. In various ways, this can be done like built-in predicates, recursion, backtracking, or a combination of these. In the above example, we define the loop predicate in terms of itself. The second clause read as 'to loop from N, first write the N's value, then subtract one to provide S, then loop from M'. This process will terminate using the first clause: 'when the argument is 0, then stop or do nothing'. Here the first clause is called as terminated condition. Looping a fixed number of times To execute the instruction a fixed number of times, many programming languages provide 'for loop'. In Prolog, there is no such facility available directly, but using recursion, we can obtain a similar effect, which is shown in the following programs: Loops in Prolog Example 1: This program outputs the integer value from a specified value down to 1. loop(0). loop(N) :- N>0, write('value of N is: '), write(N), nl. S is N-1, loop(S). ?- loop(4). value of N is: 4 value of N is: 3 value of N is: 2 value of N is: 1 yes
- 19. Here are somesimple clauses. The following queries yield the specified answers. How do you add the following facts? likes(mary,food). likes(mary,juice). likes(john,juice). likes(john,mary). | ?- likes(mary,food). yes. | ?- likes(john,juice). yes. | ?- likes(john,food). no. John likes anything that Mary likes John likes anyone who likes juice John likes anyone who likes themselves Example 3 :
- 20. Some Applications ofProlog Prolog is used in various domains. It plays a vital role in automation system. Following are some other important fields where Prolog is used − Prolog is used in various domains. It plays a vital role in automation system. Following are some other important fields where Prolog is used − • Intelligent Database Retrieval • Natural Language Understanding • Specification Language • Machine Learning • Robot Planning • Automation System • Problem Solving • Expert Systems What is Prolog used for Good at ▪ Grammars and Language processing, ▪ Knowledge representation and reasoning, ▪ Unification, ▪ Pattern matching, ▪ Planning and Search. i.e. Prolog is good at Symbolic AI. ?
- 21. 23 Advantages : 1. Easyto build database. Doesn’t need a lot of programming effort 2. Pattern matching is easy. Search is recursion based .3. It has built in list handling. Makes it easier to play with any algorithm involving lists. 2. Sometimes input and output is not easy. Disadvantages : 1. LISP (another logic programming language) dominates over prolog with respect to I/O features 3. Repetitive number crunching, Representing complex data structures, Input/output (interfaces).