A Taste of Prolog - thagomizer.com · • This is just an introduction Thursday, August 2, 12. ......

A Taste of PrologAja Hammerly

Thursday, August 2, 12

Basics

• I Like Prolog

• But, I'm not an expert

• This is just an introduction

What Is Prolog

• A logic programing language

• A declarative programming language

• A weird programming language

• Natural Language Processing

• Grammars

• Theorem Proving

• Expert Systems and other AI

Why Learn Prolog

• Expand your toolbox

• New perspective

• Become a polyglot

Prolog - Weirdness

• “What”, not “How”.

• Programs are expressed as:

• Facts

• Rules

“A computation of a logic program is a deduction of consequences of the

program. A program defines a set of consequences, which is its meaning.

The art of logic programming is constructing concise and elegant programs that have the desired

meaning.”

- The Art of Prolog

Seattle.rb Pairing

editor(zenspider, emacs).editor(drbrain, vim).editor(phiggins, vim).editor(tenderlove, vim).

?- editor(zenspider, emacs).yes

?- editor(zenspider, vim).no

Questionseditor(zenspider, emacs).editor(drbrain, vim).

?- editor(drbrain, Editor).Editor = vim

Questionseditor(zenspider, emacs).editor(drbrain, vim).

editor(zenspider, emacs).editor(drbrain, vim).

?- editor(Person, Editor).Person = zenspiderEditor = emacs

Questions

?- editor(Person1, vim), editor(Person2, vim),

Person1 \== Person2.Person1 = drbrainPerson2 = tenderlove

Questionseditor(zenspider, emacs).editor(drbrain, vim).editor(tenderlove, vim).

?- editor(Person1, Editor), editor(Person2, Editor),

Person1 \== Person2.Editor = vimPerson1 = drbrainPerson2 = tenderlove

Questionseditor(zenspider, emacs).editor(drbrain, vim).editor(tenderlove, vim).

pair(Person1, Person2) :- editor(Person1, Editor), editor(Person2, Editor), Person1 \== Person2.

?- pair(Person1, Person2).Person1 = drbrainPerson2 = tenderlove

Questions & Ruleseditor(zenspider, emacs).editor(drbrain, vim).editor(tenderlove, vim).

?- pair(drbrain, Person2).Person1 = tenderlove

?- pair(Person1, Person2).

Person1 = drbrainPerson2 = tenderlove ? ;

Person1 = drbrainPerson2 = phiggins ? ;

Person1 = tenderlovePerson2 = drbrain ?

Questions

pair(Person1, Person2) :- editor(Person1, Editor), editor(Person2, Editor), Person1 @> Person2.

?- pair(Person1, Person2).Person1 = tenderlovePerson2 = drbrain

?- pair(Person1, Person2).

Person1 = tenderlovePerson2 = drbrain ? ;

Person1 = tenderlovePerson2 = phiggins ? ;

Person1 = phigginsPerson2 = drbrain ?

Questions

keyboard(zenspider, dvorak).keyboard(drbrain, dvorak).keyboard(tenderlove, qwerty).keyboard(phiggins, qwerty).

?- keyboard(drbrain, Keyboard).Keyboard = dvorak

Questionskeyboard(zenspider, dvorak).keyboard(drbrain, dvorak).

pair(Person1, Person2) :- keyboard(Person1, Keyboard), keyboard(Person2, Keyboard), Person1 @> Person2.

?- pair(Person1, Person2).Person1 = zenspiderPerson2 = drbrain

pair(P1, P2) :- editor( P1, Editor), editor( P2, Editor), P1 @> P2.pair(P1, P2) :- keyboard(P1, Keyboard), keyboard(P2, Keyboard), P1 @> P2.

Two Rules

?- pair(X, Y).

X = tenderlove, Y = drbrainX = tenderlove, Y = phigginsX = phiggins, Y = drbrainX = zenspider, Y = drbrainX = tenderlove, Y = phiggins

Questions

super_pair(Person1, Person2) :- editor(Person1, Editor), editor(Person2, Editor), keyboard(Person1, Keyboard), keyboard(Person2, Keyboard), Person1 @> Person2.

?- super_pair(Person1, Person2).

Person1 = tenderlovePerson2 = phiggins

Questionseditor(phiggins, vim).editor(tenderlove, vim).keyboard(tenderlove, qwerty).keyboard(phiggins, qwerty).

Pattern Matching

• In prolog pattern matching is used to pass arguments.

• For example:

• human(X) will match human(bill)

• Pattern matching with variables is called unification

List Basics

Examples

• []

• [1, 2, 3]

• [apples, bananas]

• [1, lemon]

• [[1, lemon], [1, lime], [2, coconuts]]

Heads and Tails

• [1, 2, 3]

• 1 is the head

• [2, 3] is the tail

• [H | T] (read: "H bar T")

• [H | T] matches with [1, 2, 3] as [1|[2,3]]

Don't Care• ‘_’ means I don't care

• [1, _, 3] could be

• [1, 2, 3] or

• [1, pi, 3] or

• [1, [apple, pie], 3]

• 2 don't cares can refer to different values

def member(x, ary) return false if ary == [] return true if ary[0] == x member(x, ary[1..-1])end

Member

def member(x, ary) return false if ary == [] return true if ary[0] == x member(x, ary[1..-1])end

Member

member(H, [H | _]).member(X, [_ | T]):- member(X, T).

?- member(2, [1, 2, 3]).

?- member(6, [1, 2, 3]).

?- member(X, [1, 2, 3]).

X = 1 ? a

?- member(6, X).

X = [6|_] ? ;

X = [_,6|_] ? ;

X = [_,_,6|_] ?

Variables Anywhere

def length(ary) return 0 if ary == [] return length(ary[1..-1]) + 1end

Length

def length(ary) return 0 if ary == [] return length(ary[1..-1]) + 1end

Length

length([], 0).length([_ | T], N) :- length(T, N1), N is N1 + 1.

?- length([a, b, c, d], 4).

?- length([1, 2, 3], X).

?- length(X, 2).

X = [_,_]

Circuits

In Outinv(0, 1).inv(1, 0).

A B Outor(0, 0, 0).or(1, 0, 1).or(0, 1, 1).or(1, 1, 1).

A B Outand(0, 0, 0).and(0, 1, 0).and(1, 0, 0).and(1, 1, 1).

A B Outxor(0, 0, 0).xor(0, 1, 1).xor(1, 0, 1).xor(1, 1, 0).

A B Outnand(0, 0, 1).nand(0, 1, 1).nand(1, 0, 1).nand(1, 1, 0).

half_adder(A, B, C, S) :- xor(A, B, S), and(A, B, C).

?- half_adder(A, B, C, S).

A = 0, B = 0, C = 0, S = 0

A = 0, B = 1, C = 0, S = 1

A = 1, B = 0, C = 0, S = 1

A = 1, B = 1, C = 1, S = 0

full_adder(A, B, Cin, Cout, S) :- half_adder(A, B, C1, S1), half_adder(Cin, S1, C2, S), or(C1, C2, Cout).

?- full_adder(A, B, 1, Cout, 1).

A = 0, B = 0, Cout = 0A = 1, B = 1, Cout = 1

? - full_adder(A, B, Cin, 1, S).

A = 0, B = 1, Cin = 1, S = 0A = 1, B = 0, Cin = 1, S = 0A = 1, B = 1, Cin = 0, S = 0A = 1, B = 1, Cin = 1, S = 1

mystery(A, B, D) :- nand(A, B, T1), nand(A, T1, T2), nand(B, T1, T3), nand(T2, T3, D).

?- mystery(A, B, D).

A = 0, B = 0, D = 0

A = 0, B = 1, D = 1

A = 1, B = 0, D = 1

A = 1, B = 1, D = 0

Logic PuzzlesThursday, August 2, 12

Apartment Building1. Adam does not live on the top floor.

2. Bill does not live on the bottom floor.

3. Cora does not live on either the top or the bottom floor.

4. Dale lives on a higher floor than does Bill.

5. Erin does not live on a floor adjacent to Cora's.

6. Cora does not live on a floor adjacent to Bill's.

‘Data Structure’

• A list of the people, ordered by floor

• [Top, Floor4, Floor3, Floor2, Bottom]

• [adam, bill, cora, dale, erin]

adam \== Top,

Adam does not live on the top floor.

bill \== Bottom,

Bill does not live on the bottom floor.

cora \== Top,cora \== Bottom,

Cora does not live on either the top or the bottom floor.

higher(dale, bill, L),

Dale lives on a higher floor than does Bill.

higher(X, Y, [X | T]) :- member(Y, T).

higher(X, Y, [_ | T]) :- higher(X, Y, T).

Higher

not_adjacent(erin, cora, L),

Erin does not live on a floor adjacent to Cora's.

not_adjacent

not_adjacentnot_adjacent(X, Y, [X, Z | T]) :- Z \== Y,

member(Y, T).

not_adjacent

not_adjacent(X, Y, [Y, Z | T]) :- Z \== X, member(X, T).

not_adjacent(X, Y, [X, Z | T]) :- Z \== Y,

member(Y, T).

not_adjacent(X, Y, [_ | T]) :- not_adjacent(X, Y, T).

not_adjacent

not_adjacent(X, Y, [Y, Z | T]) :- Z \== X, member(X, T).

not_adjacent(X, Y, [X, Z | T]) :- Z \== Y,

member(Y, T).

not_adjacent(cora, bill, L),

Cora does not live on a floor adjacent to Bill's.

permutation(L, [adam, bill, cora, dale, erin]).

permutation

puzzle(L) :- L = [Top, F4, F3, F2, Bottom],

Puzzle

puzzle(L) :- permutation(L, [adam, bill, cora, dale, erin]), L = [Top, Floor4, Floor3, Floor2, Bottom], adam \== Top, bill \== Bottom, cora \== Top, cora \== Bottom, higher(dale, bill, L), not_adjacent(erin, cora, L), not_adjacent(cora, bill, L).

All Together

| ?- puzzle([A, B, C, D, E]).

A = daleB = coraC = adamD = billE = erin ? ;

Running

Learn More

Books• Sterling, Leon & Shapiro, Ehud. The Art of Prolog

• Clocksin, William F. Clause and Effect: Prolog Programming for the Working Programmer

• Bratko, Ivan. Prolog Programming for Artificial Intelligence

• Tate, Bruce A. Seven Languages in Seven Weeks: A Pragmatic Guide to Learning Programming Languages

Thank You

A Taste of Prolog - thagomizer.com · • This is just an introduction Thursday, August 2, 12. ......

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