QuickStart Prolog

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QuickStart Prolog

• Learning to Program in Prolog
• Richard Banister
• November 9, 2005

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What is Prolog?

• A Logical Programming Language
• Why logical?
• Created by Robert Kowalski and Alain Colmerauer
  sometime around 1972.
• Original intended for natural language parsing
• Now used in AI, expert systems

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The Logical Paradigm

• Based on logical reasoning
• Execution as mathematical proof
• Non-sequential design
• Fun!

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Prolog as a Logical Language

• Predicates are entered into a database
• Rules are created
• Queries are run against said predicates and rules
• Results are determined only from what is known to
  be true
• Well, how do we do anything?

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A Logical Example

• Take this example
• cat(Timmy).legs(cat, 4).?- legs(Timmy, 4)yes
• Yeah!
• We can also do useful stuff

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Prolog Advantages

• Its a Logical Programming language
• Its the only game in town
• Thats about it.

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Prolog Disadvantages

• Limited sphere of usefulness
• Not a pure logical language
• It dont have the fancy graphics the youngsters
  are raving about
• It wont make you popular with the ladies

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Java or Prolog?

• Kind of a silly question
• Depends greatly on project goal
• Prolog for web app not a good idea
• Java for robot army maybe not a good idea
  either
• Yet they are being combined together as we speak

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Prolog Specification

• Well, its a funny story
• Prolog spec available for a price
• Grammar is not reprintable on web
• Decidedly geek-non-friendly
• This, along with late spec publication (1995!),
  may be why Prolog hasnt taken over the world?
• But we do know some things about the grammar

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Prolog Grammar

• A free approximate grammar can be found online
  (https//www.freytag.us/twiki/bin/view/Freytag/ISO
  StandardPrologGrammar)
• Heres a sample

• Possibly not complete, but note simplicity

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Is Prolog Dead?

• Not quite. Still kicking in AI
• New extensions are being developed
• Visual Prolog
• Prova

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Language Specifics

• PredicateA statement given to be true ex.
  cat(Timmy).
• RuleA method for proving future resultsex.
  cat(X) - legs(4, X), whiskers(X),
  intent_to_destroy(X).
• QueryA request to prove a resultex.
  whiskers(Uncle Jerry). Intent_to_destroy(Uncle
  Jerry). Legs(1, Uncle Jerry). ?- cat(Uncle
  Jerry). no

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Step 0 Getting Started

• Get to know logical programming and Prolog
• There are many websites that contain useful, if
  cryptic, Prolog information.

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Step 1 Really Getting Started

• Download install GNU interpreterhttp//pauilla
  c.inria.fr/diaz/gnu-prolog/
• You can get the source, too, if you really want
  it
• Read up the GNU interpreter isnt easy

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Step 2 Writing

• Create a plain text file
• Some editors have context-sensitive highlighting,
  but its probably not necessary
• File should contain predicates and rules, not
  queries
• Create a legendary, essential logical application
  (maybe, dog(Rover)?)

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Step 3 Import Source File

• Start the interpreter.
• Use the consult command (or shortcut) to open and
  compile the source codeex. consult(/projects/pro
  log/cat.pl).
• Note the use of Unix-style file reference. This
  isnt necessarily documented in the help file.
• Assuming no errors, run queries on your program

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Learning more about Prolog

• Visit the QuickStart Languages web
  sitehttp//actlab.csc.villanova.edu/quickstart
• Read up on logical languageshttp//en.wikipedia.o
  rg/wiki/Logic_programming
• Devote your life to this tutorialhttp//web.archi
  ve.org/web/20041028043137/http//cs.wwc.edu/cs_de
  pt/KU/PR/Prolog.html