QuickStart Languages - Learn to program step-by-step

QuickStart Prolog

by Richard Banister

Step-by-step instructions for learning to program in Prolog

About the language

Name:	Prolog
Year created:	1972
Created by:	Alain Colmerauer, Robert Kowalski
Paradigm:	Logical
Platform:	Runs on any platform that has an interpreter. Basic code should be platform-independent, so it should run the same on each interpreter across platforms. Interpreters exist for Unix-based systems, Windows systems, and Macintosh systems, among others. Also available is a Java interpreter applet.
Domain:	Natural language parsing, AI, expert systems
Advantages:	Logical paradigm
Disadvantages:	Logical paradigm - not terribly easy to mimic sequential design; standard is not freely available; harder to find good beginners tutorials and information online
Specification:	Official spec is not freely available online. Information about the spec can be found at http://pauillac.inria.fr/~deransar/prolog/docs.html
Grammar:	Again, the spec isn't available online. A few people have reverse-engineered the approximate grammar; it can be found at https://www.freytag.us/twiki/bin/view/Freytag/ISOStandardPrologGrammar

Step 1. Download a Prolog Interpreter

The GNU interpreter is serviceable and fairly well documented. But any Prolog interpreter will do
Go to the GNU Prolog site (http://pauillac.inria.fr/~diaz/gnu-prolog/), and scroll down to the download section
Download the installer for your platform. Windows and Unix-flavors are available
Run the installer. It probably won't install any viruses
Run the interpreter, and try to hack your way through. Consult the documentation, if needs be

Step 2. Writing a Program

Any ol' text editor will do
Save your program somewhere easy to remember, and most importantly, easy to type (ex. "C:\prolog\hello.pl")
Load the program into the interpreter in this fashion:
- type consult('/path/filename'). in the interpreter
- path is the directory on disk where your program is located, in unix-style notation
- filename is the name of your file
- So, you would type, for example, consult('/prolog/hello.pl').
- Note that ['/prolog/hello.pl']. can be used as shorthand for the consult predicate
You can also enter your program directly into the interpreter by typing [user].

Step 3. Write a "hello world" program

At the ?- prompt, type write('hello world').

Step 4. Explore the possibilities

Try some more demos. This simple logical process was taken from http://www.csse.monash.edu.au/~lloyd/tildeLogic/Prolog.toy/Examples/

witch(X)  :- burns(X), female(X).
burns(X)  :- wooden(X).
wooden(X) :- floats(X).
floats(X) :- sameweight(duck, X).

female(girl).          
sameweight(duck,girl).

Prolog can do calculations, too

Look at the demos at this site for some serious examples.

What about recursive descent parsing?

Here's a snippet of a familiar grammar:

	
			program		-->  evallist, eof.
			evallist	-->  evalexpr, evallist ; evalexpr.
			evalexpr	-->  ...

See the websites below for more extensive examples

Learning more

Despite lacking an official site, there are a number of sources of information on Prolog online.

Prolog Wikipedia Entry - A good overview of the language and its purpose
Prolog Grammar - A reverse-engineered grammar for Prolog.
Some silly examples - Explains the basics of the language with some easy demos. Each demo is runnable in the browser.
A Massive Prolog Tutorial - Very in-depth look at all the features of Prolog. Not for the weak of heart.
Small example programs - reasoning about cats and witches

QuickStart Presentation

Download and view the QuickStart Prolog PowerPoint Presentation.

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