(This document is in process, it will be\u00a0continually\u00a0updated until\u00a0completion. Please be patience).<\/p>\n
Right now, I am learning how to program in PROLOG (PROgramming in LOGic) in my course of programming languages at Binghamton University.\u00a0I must confess that I find it to be very different to what I thought it would looks like.<\/p>\n
Prolog was mainly used for\u00a0artificial\u00a0intelligence and computational linguistics (http:\/\/en.wikipedia.org\/wiki\/Prolog<\/a>). I would really like to know if it is used outside of the academic environment. If anyone have any info about this let me know.<\/p>\n The following article at http:\/\/www.kuro5hin.org\/story\/2004\/2\/25\/124713\/784<\/a> written by tkatchev<\/a> says that Prolog can be used for hacking. Even do I agree with tkatchev that is\u00a0plausible, I would love to see an actual example. Some encryption braking, etc. \u00a0Also, I agree that the way it is presented could be more effective if applied to real life uses than IA.<\/p>\n At the bottom I will add a list of links related with this topic.<\/p>\n Prolog is a programming language that let the programmer write a declarative program instead of a procedural program. Just to make sure we are in the same page, a declarative program is when the programmer used “truth and logical deduction” (Bart\u00e1k<\/a><\/em>). <\/em>In declarative programming, the programmer must use a\u00a0descriptive\u00a0style that let know which are the relationship between the entities (Brna). Prolog perform the execution of the program in an tree dept-first fashion or other way to call it: First Order Predicate Logic. Later I will go more in deep and clarify this.<\/p>\n Let start with installing the basics:<\/strong><\/p>\n Prolog works using atoms, terms, variables, facts, rules, recursion, and queries between others. Little by little we will be introducing this concepts.<\/p>\n Lets analyse the following examples:<\/strong><\/p>\n 1. pens have inside ink<\/p>\n a. This should be written as:<\/p>\n have_inside(pens, ink).<\/span><\/em><\/p>\n b. Notice that pens and ink do not have the first letter in capital. Words that are start with capital letters are considerate logical variables.<\/p>\n Logical Variable: Pens<\/em><\/p>\n No logical variable: pens<\/em><\/p>\n c. A predicate cannot be a logical variable<\/p>\n Wrong:<\/span> Have_inside(pens, ink).<\/em><\/p>\n Correct:<\/span> have_inside(pens, ink).<\/span><\/em><\/p>\n d. pens<\/em> and ink<\/em> are called atoms<\/em> (or constants<\/em>).<\/p>\n e. This functor<\/em> is a prefix called a relationship<\/em> (or predicate<\/em>).<\/p>\n f. This predicate<\/em> have a arity<\/em> (number of arguments) of 2.<\/p>\n i. A predicate<\/em> with no arguments is a single proposition<\/em>, a predicate<\/em> with one argument is unary<\/em>,\u00a0with two arguments is binary<\/em>, with three arguments is ternary<\/em>, …<\/p>\n g. This is a clause therefore they must end with a period (.) and an space after or with a period(.) and a new line.<\/p>\n h. More examples:<\/p>\n i. pepe is bold:<\/p>\n bold(pepe).<\/span><\/em><\/p>\n ii. juan saw tim by the coffe shop:<\/p>\n saw(juan, tim, coffee_shop).<\/span><\/em><\/p>\n 2. In the previous example, we named atoms<\/em> (or\u00a0constants<\/em>) and logical variables<\/em><\/p>\n a. Examples of atoms<\/em>:<\/p>\n countryA, –+–, \u00a0‘Hello World’<\/em> (Notice that we are using a single tilde (”) not a double tilde (“”))<\/p>\n 3. Difference between a goal<\/em> and a unit clause<\/em><\/p>\n a. Goal:<\/p>\n miss(maria, jose)<\/span><\/em><\/p>\n b. Unit Clause:<\/p>\n miss(maria, jose).<\/span><\/em><\/p>\n What are the difference between both? The period at the end. A goal<\/em> is called a unit<\/em> while a clause<\/em> is called a non-unit<\/em>. More details about this later.<\/p>\n 4. Multi Clause: We can have more than one clause with the same name for example:<\/p>\n square_root(1, 1). In this case we are saying: the square root of 1 is 1 OR the square root of 4 is 2 OR the square root of 9 is 3. 5. Rules:\u00a0Rules<\/em> are non-unit<\/em> conditionals in Prolog. For example:<\/p>\n a. If tim have a job, then tim can pay his bills<\/p>\n can_pay_bills(tim) :- <\/span><\/em><\/p>\n have_job(tim).<\/span><\/em><\/p>\n i. :-<\/em> is the equivalent of if<\/em><\/p>\n ii. This is a non-unit clause<\/em><\/p>\n b.Let say we want to use a rule with a variable:<\/p>\n i. if a number is divisible by 1 AND also the number is divisible by three then the number is odd<\/p>\n number_is_odd(X) :-<\/span><\/em><\/p>\n number_divisible_by_one(X),<\/span><\/em><\/p>\n number_divisible_by_three(X)<\/span><\/em>.<\/span><\/p>\n I. The comma (,) is the representation of the statement AND. If number_divisible_by_one is true AND number_divisible_by_three \u00a0 \u00a0 is true, then number_is_odd is true.<\/p>\n ii. classes are cancel if the day is a holiday OR the professor is sick<\/p>\n cancel(classes) :-<\/span><\/em><\/p>\n day_is_holiday(classes).<\/span><\/em><\/p>\n cancel(classes) :-<\/span><\/em><\/p>\n proffesor_is_sick(classes).<\/span><\/em><\/p>\n iii. There is an special case in which two rules seems to be talking about the same variable but they are not:<\/p>\n number_is_divisible_by_two(X) :-<\/span><\/em><\/p>\n number_is_odd(X).<\/span><\/em><\/p>\n number_is_divisible_by_two(X) :-<\/span><\/em><\/p>\n number_is_odd(X).<\/span><\/em><\/p>\n I. In this case it says that a number is divisible by one is the number is odd or a number is divisible by three if the number is odd. Believed or not, we are not talking about the same variable. Why? Because “local variables cannot be overwritten with a new value”<\/span><\/span> (Paul Brna). Example:<\/p>\n A. if we say that X = 1 and later we try to change this variable (X = 2) this will not work for Prolog<\/p>\n I will try to continue this topic in another posting.<\/p>\n \n \n \n \n <\/em><\/p>\n \n \n \n Related Links:<\/p>\n Work Citied<\/em><\/p>\n Roman Bart\u00e1k<\/a>, <\/em>http:\/\/kti.mff.cuni.cz\/~bartak\/prolog\/intro.html<\/a><\/em><\/span><\/p>\n Paul Brna,\u00a0http:\/\/homepages.inf.ed.ac.uk\/pbrna\/prologbook\/node11.html<\/a><\/em><\/em><\/span><\/p>\n\n
\nIn a\u00a0procedural\u00a0program, the programmer indicate the machine what to do, step by step.<\/p>\n\n
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\nsquare_root(4, 2).
\nsquare_root(9, 3).<\/span><\/em><\/p>\n
\nEvery time you use the period(.) and a newline, this is the equivalent of saying OR.<\/p>\n\n