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Programming Languages
Tevfik Koşar
Lecture - XIX
March 28th, 2006
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Roadmap
• Logic Languages
– Predicate Calculus
• Prolog Programming Language
– Basics
– Queries
– Resolution
– Unification
– Lists
– Running Prolog Programs
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Logic Programming with Prolog: Lecture Notes by Tevfik Koşar, Study notes of Programming Languages
A set of lecture notes on logic programming with prolog by tevfik koşar. The notes cover topics such as logic languages, prolog programming language, logic programming, prolog queries, resolution, unification, lists, and arithmetic. The document also includes examples and exercises.
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1
Programming Languages
Tevfik Koşar
Lecture - XIX March 28th, 2006
2
Roadmap
- Logic Languages
- Predicate Calculus
- Prolog Programming Language
- Basics
- Queries
- Resolution
- Unification
- Lists
- Running Prolog Programs
3
Logic Programming
- Based on predicate calculus
- (Functional lang. were based on Lambda Calculus)
- Predicates - building-blocks P(a 1 ,a 2 ,...,aK)
- Define relationships between entities
- Eg:
- enrolled(john, cs4101)
- taught_by(cs4101, dr_kosar)
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Logic Programming
- Axioms: define logic rules between predicates
- H B 1 , B 2 , B 3 , ….. Bn
- Eg:
- takes_class_from(X,Y) enrolled (X,Z), taught_by(Z,Y)
- enrolled(john, cs4101)
- taught_by(cs4101, dr_kosar)
takes_class_from(john, dr_kosar)
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Prolog
- Prolog predicates/facts:
- rainy(baton_rouge).
- teaches(dr_kosar, csc4101).
- Predicates/clauses end with ‘.’
- Predicates are called facts, and axioms are called rules
- Prolog axioms/rules:
- snowy(X) :- rainy(X), cold(X).
- ‘:-’ is the implication symbol
- ‘,’ indicates ‘and’.
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Prolog Queries
rainy(seattle).
rainy(newyork).
?- rainy(X).
X = seattle;
X = newyork;
no
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Prolog Queries
rainy(seattle).
rainy(rochester).
cold(rochester).
snowy(X) :- rainy(X), cold(X).
?- snowy(X).
X = rochester;
no
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Resolution
- C A, B
- D C
- Resolution: D A, B
- takes (jane, csc4101).
- classmates(X,Y) :- takes(X,Z), takes(Y,Z).
- Resolution: classmates(jane, Y) :- takes(Y, csc4101)
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Unification
- takes_lab(S) :- takes(S, C), has_lab(C).
- has_lab(D) :- meets_in(D, R), is_lab(R).
takes_lab(S) :- takes(S, C), meets_in(C, R), is_lab(R).
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Lists
- [a, b, c] can be expressed as (using vertical bar notation):
- [a | [b, c]]
- [a, b | [c]]
- [a, b, c | []]
- member(X, [X|T]).
- member(X, [H|T]) :- member(X, T).
- sorted([]).
- sorted([X]).
- sorted([A, B | T]) :- A <= B, sorted([B | T]).
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Lists
append([], A, A). append(H | T), A, [H | L]) :- append(T, A, L).
?- append([a, b, c], [d, e], L). L = [a , b, c, d, e] ?- append(X, [d, e], [a, b, c, d, e]). X = [a, b, c] ?- append([a, b, c], Y, [a, b, c, d, e]). Y = [d, e]
Prolog predicates do not have a clear distinction between input and output arguments!
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Arithmetic
- Built-in is predicate: unifies its first argument with the arithmetic value of its second argument.
?- is(X, 1+2). X = 3 ?- X is 1+2. X = 3 ?- 3 is 1+2. yes ?- 1+2 is 3. no ?- X is Y.