AI::Prolog

Curtis "Ovid" Poe

Presented by

• Shaun Griffith

• Toronto Perl Mongers

• September 29, 2005

What is Prolog?

What is Prolog?

Not a "Professional Logger"

What is Prolog?

Not a "Professional Logger"

Quoting Ovid:

• In Perl, we traditionally tell the language how to find a solution.

• In Prolog, we describe what a solution would look like and let the language find it for us.

What is Prolog?

Not a "Professional Logger"

Quoting Ovid:

• In Perl, we traditionally tell the language how to find a solution.

• In Prolog, we describe what a solution would look like and let the language find it for us.

From Wikipedia:

• From the French programmation en logique

• A Logic Programming language created in 1972

• Predicate calculus (first order)

• Declarative programming style

What does Prolog do?

Prolog:

• Looks good in Flannel

• Understands facts, rules, and queries.

• Solves logic puzzles

  • Three men, Mr. Smith, Jones, and Wilson, each had one of three...

  • Su Doku

• Proves theorems

• Plays Adventure

Prolog Example

Family Tree (Stumps)

   % Facts
   male(tom).
   father(tom, sally).
   father(tom, erica).
   father(mike, tom).

   % Rules
   father(X,Y)  :- parent(X,Y), male(X).
   parent(X,Y)  :- father(X,Y).

   % Interactive Queries
   ?- parent(tom, sally)
        yes.
   ?- father(X,tom)
        mike.

Facts

Relation Applies To

   % Facts
   %     predicate(term, ...)
   %     atoms are lowercase or quoted

Facts

Relation Applies To

   % Facts
   %     predicate(term, ...)
   %     atoms are lowercase or quoted

   % tom is male  ( male/1 )
   male(tom).

Facts

Relation Applies To

   % Facts
   %     predicate(term, ...)
   %     atoms are lowercase or quoted

   % tom is male  ( male/1 )
   male(tom).

   % tom is the father of sally ( father/2 )
   father(tom, sally).

Facts

Relation Applies To

   % Facts
   %     predicate(term, ...)
   %     atoms are lowercase or quoted

   % tom is male  ( male/1 )
   male(tom).

   % tom is the father of sally ( father/2 )
   father(tom, sally).

   father(tom, erica).
   father(mike, tom).

Rules

If and only If

   % Rules
   %    predicate(...) :- predicate(...), ....
   %    AND is comma
   %    OR is semi-colon or multiple rules

Rules

If and only If

   % Rules
   %    predicate(...) :- predicate(...), ....
   %    AND is comma
   %    OR is semi-colon or multiple rules

   % a father is a male AND a parent
   father(X,Y) :- parent(X,Y), male(X).

Rules

If and only If

   % Rules
   %    predicate(...) :- predicate(...), ....
   %    AND is comma
   %    OR is semi-colon or multiple rules

   % a father is a male AND a parent
   father(X,Y) :- parent(X,Y), male(X).

   % a parent is a father OR mother
   parent(X,Y)  :- father(X,Y).
   parent(X,Y)  :- mother(X,Y).

Queries

What can be proved?

    % Queries
    %    interactive prompt ?-
    %    verify a fact
    ?- father(tom, erica).

         yes.

Queries

What can be proved?

    % Queries
    %    interactive prompt ?-
    %    verify a fact
    ?- father(tom, erica).

         yes.

    %    fill in the blanks
    ?- father(X,tom)

         mike.

Queries

What can be proved?

    % Queries
    %    interactive prompt ?-
    %    verify a fact
    ?- father(tom, erica).

         yes.

    %    fill in the blanks
    ?- father(X,tom)

         mike.

    ?- mother(tom,X)

         no.

Using AI::Prolog

    use AI::Prolog;
    use Data::Dumper; 

Using AI::Prolog

    use AI::Prolog;
    use Data::Dumper; 

    my $program_string = <<'END_PROLOG';

Using AI::Prolog

    use AI::Prolog;
    use Data::Dumper; 

    my $program_string = <<'END_PROLOG';

       % Facts
       male(tom).
       father(tom, sally).
       father(tom, erica).
       father(mike, tom).

Using AI::Prolog

    use AI::Prolog;
    use Data::Dumper; 

    my $program_string = <<'END_PROLOG';

       % Facts
       male(tom).
       father(tom, sally).
       father(tom, erica).
       father(mike, tom).

       % Rules
       father(X,Y)  :- parent(X,Y), male(X).
       parent(X,Y)  :- father(X,Y).

Using AI::Prolog

    use AI::Prolog;
    use Data::Dumper; 

    my $program_string = <<'END_PROLOG';

       % Facts
       male(tom).
       father(tom, sally).
       father(tom, erica).
       father(mike, tom).

       % Rules
       father(X,Y)  :- parent(X,Y), male(X).
       parent(X,Y)  :- father(X,Y).

    END_PROLOG

Using AI::Prolog

    use AI::Prolog;
    use Data::Dumper; 

    my $program_string = <<'END_PROLOG';

       % Facts
       male(tom).
       father(tom, sally).
       father(tom, erica).
       father(mike, tom).

       % Rules
       father(X,Y)  :- parent(X,Y), male(X).
       parent(X,Y)  :- father(X,Y).

    END_PROLOG

    my $prolog = AI::Prolog->new($program_string);

Using AI::Prolog

    use AI::Prolog;
    use Data::Dumper; 

    my $program_string = <<'END_PROLOG';

       % Facts
       male(tom).
       father(tom, sally).
       father(tom, erica).
       father(mike, tom).

       % Rules
       father(X,Y)  :- parent(X,Y), male(X).
       parent(X,Y)  :- father(X,Y).

    END_PROLOG

    my $prolog = AI::Prolog->new($program_string);

    $prolog->query("father(X,tom).");

Using AI::Prolog

    use AI::Prolog;
    use Data::Dumper; 

    my $program_string = <<'END_PROLOG';

       % Facts
       male(tom).
       father(tom, sally).
       father(tom, erica).
       father(mike, tom).

       % Rules
       father(X,Y)  :- parent(X,Y), male(X).
       parent(X,Y)  :- father(X,Y).

    END_PROLOG

    my $prolog = AI::Prolog->new($program_string);

    $prolog->query("father(X,tom).");

    while (my $result = $prolog->results())
    {  print Dumper $result; }

Using AI::Prolog

    use AI::Prolog;
    use Data::Dumper; 

    my $program_string = <<'END_PROLOG';

       % Facts
       male(tom).
       father(tom, sally).
       father(tom, erica).
       father(mike, tom).

       % Rules
       father(X,Y)  :- parent(X,Y), male(X).
       parent(X,Y)  :- father(X,Y).

    END_PROLOG

    my $prolog = AI::Prolog->new($program_string);

    $prolog->query("father(X,tom).");

    while (my $result = $prolog->results())
    {  print Dumper $result; }

    $VAR1 = [ 'father', 'mike', 'tom' ];

Info and Resources

!!! Alpha Release !!!

• Implementation based on W-Prolog, by Dr. Michael Winikoff.

• Some features stolen from X-Prolog.

AI::Prolog on CPAN:

• http://search.cpan.org/~ovid/AI-Prolog-0.732/lib/AI/Prolog.pm

Roman Barták's online programming guide:

• http://kti.ms.mff.cuni.cz/~bartak/prolog/index.html

Adventure in Prolog

• http://www.amzi.com/AdventureInProlog/advfrtop.htm

Wikipedia:

• http://en.wikipedia.org/wiki/Prolog