1 / 24

Introduction to Prolog Brian Paden

Introduction to Prolog Brian Paden. History. Creators: Alain Colmerauer & Phillipe Roussel University of Aix-Marseille 1972 Robert Kowalski University of Edinburgh Named by: Philippe Roussel programmation en logique First compiler: David H. D. Warren. More History.

sutton
Download Presentation

Introduction to Prolog Brian Paden

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. P-Phunck - Prolog Introduction to Prolog Brian Paden

  2. P-Phunck - Prolog History • Creators: Alain Colmerauer & Phillipe Roussel • University of Aix-Marseille 1972 • Robert Kowalski • University of Edinburgh • Named by: Philippe Roussel • programmation en logique • First compiler: David H. D. Warren

  3. P-Phunck - Prolog More History • 1984 – Began working on standard • 1987 – ISO Standard Group Formed • 1995 – ISO Standard published • Most current • New version expected “by early 2000”

  4. P-Phunck - Prolog Predicate Logic • First order predicate calculus • Propositions • Atomic propositions & compound terms • Resolution • Inference rule • Horn clauses • Single atomic proposition on left side • Empty left side

  5. P-Phunck - Prolog Data Types • Atom • Letters or numbers 'x', 'longConstant17', '“Var”' • Variable • Start with uppercase 'X', 'NotanAtom' • Anonymous variable - '_' • Fact • 'doesntKnow( “Prolog”, brian ).'

  6. P-Phunck - Prolog Variables • Two states • Instantiated • Variable has a set value • Uninstantiated • Has not been assigned a value • Closed-world assumption • Only true if it can be proven

  7. P-Phunck - Prolog Data Structures • Compound term • Functor and arguments • 'weird( prolog, yes ).' • Queries • '?- good( presentation, brian )' • Only returns 'yes' or 'no' • Conjunction • Multiply queries and facts

  8. P-Phunck - Prolog Special Compound Terms • List • Head • First element in list • Tail • List containing everything else in list except the head • Last element is empty list - '[]' • '[]', '.' - '[a,[b,[c]]]' == 'a.b.c.[]' • String • Special list – all elements are atoms • '[“This”,is,a,string,in,”Prolog”]'

  9. P-Phunck - Prolog More Lists • Special list operators • '[]' - Empty list • '[X|Y]' – X is head, Y is tail • '””' - convert list to list containing ascii values • Recursive search for element of list member(X,[X|_]). member(X,[_|Y]) :- member(X,Y). ?- member(c,[a,b,c,d,e,f]). yes

  10. P-Phunck - Prolog Built in Operators • Compound construction • ',' - conjunction, ';' - disjunction • Comparison • 'X = Y' – equality, 'X \= 2' – inequality • 'X == Y' – strict equality, 'X \== 2' – strict inequality • 'X < Y', 'X =< Y', - less than, less than equal to • 'X > Y', 'X >= Y' – greater than, greater than equal to • Arithmetic • 'X + Y', 'X - Y', 'X * Y', 'X / Y', 'X mod Y'

  11. P-Phunck - Prolog Arithmetic • Operators that stand out • '\' - not, '\=' - not equal • '=<' - less equal, '>=' - greater equal • Perform arithmetic • 'is' • ' Y = Y/X' – tests equality • 'Y is Y/X' – assigns numeric value to Y • Right hand side of 'is' must be algebraic

  12. P-Phunck - Prolog Looping • No iteration, only recursion factorial(0,1). factorial(N,F) :- N>0, N1 is N-1, factorial(N1,F1), F is N * F1. ?- factorial(3,X). X=6

  13. P-Phunck - Prolog I/O • Special file • 'user' • Output • 'tell(X).' - creates/opens file • 'telling(X).' - gets open file name • 'told' – closes file • Input • see, seeing, seen • Misc • 'tab(X)', 'nl'

  14. P-Phunck - Prolog Backtracking • User query • Searches database for fact declaring it true • Matching fact (head rule) found • Mark place in database, move on to next goal • No matching fact found • Attempt to re-satisfy goal • Undo last change and try again • Cut • Shortcuts backtracking • '!' symbol

  15. Backtracking in Action Database Result father(mary,george). father(john,george). father(sue,harry). father(george,edward). father(X) :- father(_,X). Y=george; Y=george; Y=harry; Y=edward; no Query ?- father(Y). P-Phunck - Prolog

  16. P-Phunck - Prolog Lists and Backtracking reverse([],[]). reverse([Head|Tail],List) :- reverse(Tail,Result), append(Result,[Head],List). trace. ?- reverse([a,b,c],Q).

  17. P-Phunck - Prolog Reverse Example (1) 1 Call: reverse([a,b,c],_6)? (2) 2 Call: reverse([b,c],_65636)? (3) 3 Call: reverse([c],_65646)? (4) 4 Call: reverse([],_65656)? (4) 4 Call: Exit: reverse([],[])‏ (5) 4 Call: append([],[c],_65646)? (5) 4 Exit: append([],[c],[c])‏ (3) 3 Exit: reverse([c],[c])‏ (6) 3 Call: append([c],[b],_65636)? (7) 4 Call: append([],[b],_25)? (7) 4 Exit: append([],[b],[b])‏ (6) 3 Exit: append([c],[b],[c,b])‏ (2) 2 Exit: reverse([b,c],[c,b)‏ (8) 2 Call: append([c,b],[a],_6)? (9) 3 Call: append([b],[a],_32)? (10) 4 Call: append([],[a],_39)? (10) 4 Exit: append([],[a],[a])‏ (9) 3 Exit: append([b],[a],[b,a])‏ (8) 2 Exit: append([c,b],[a],[c,b,a])‏ (1) Exit: reverse([a,b,c],[c,b,a])‏

  18. P-Phunck - Prolog How to Cut Database Result sum_to(1,1) :- !. sum_to(N,Res) :- N1 is N – 1, sum_to(N1,Res), Res is Res + N. X = 15; no Query ?- sum_to(5,X).

  19. P-Phunck - Prolog Useful Built in Predicates • Conditional • 'true', 'fail' – Always their namesakes • 'atom(X)', 'integer(X)' – true if X is an atom or int • 'atomic(X)' – X is not a variable • 'asserta(X)' – adds clause X to start of database • 'assertz(X)' – adds clause to end of database • 'X =.. L' - Univ • X is variable • L is list where head is functor and tail is arguments

  20. P-Phunck - Prolog Example: Binary Tree Implementation Usage lookup(H,w(H,G,_,__,G) :- !. lookup(H,w(H1,_,Before,_),G) :- aless(H,H1), lookup(H,Before,G). lookup(H,w(H1,_,_,After),G) :- not(aless(H,H1)), lookup(H,After,G). ?- lookup(key,X,582), lookup(val,X,356).

  21. P-Phunck - Prolog Example: Quicksort partition([], _, [], []). partition([X|Xs], Pivot, Smalls, Bigs) :- ( X @< Pivot -> Smalls = [X|Rest], partition(Xs, Pivot, Rest, Bigs)‏ ; Bigs = [X|Rest], partition(Xs, Pivot, Smalls, Rest)‏ ). quicksort([]) --> []. quicksort([X|Xs]) --> { partition(Xs, X, Smaller, Bigger) }, quicksort(Smaller), [X], quicksort(Bigger).

  22. P-Phunck - Prolog Example: Turing Machine turing(Tape0, Tape) :- perform(q0, [], Ls, Tape0, Rs), reverse(Ls, Ls1), append(Ls1, Rs, Tape). perform(qf, Ls, Ls, Rs, Rs) :- !. perform(Q0, Ls0, Ls, Rs0, Rs) :- symbol(Rs0, Sym, RsRest), once(rule(Q0, Sym, Q1, NewSym, Action)), action(Action, Ls0, Ls1, [NewSym|RsRest], Rs1), perform(Q1, Ls1, Ls, Rs1, Rs). symbol([], b, []). symbol([Sym|Rs], Sym, Rs). action(left, Ls0, Ls, Rs0, Rs) :- left(Ls0, Ls, Rs0, Rs). action(stay, Ls, Ls, Rs, Rs). action(right, Ls0, [Sym|Ls0], [Sym|Rs], Rs). left([], [], Rs0, [b|Rs0]). left([L|Ls], Ls, Rs, [L|Rs]).

  23. P-Phunck - Prolog Compilers • ISO Compliant • GNU Prolog • http://www.gprolog.org/ • SWI-Prolig • http://www.swi-prolog.org/ • YAP • http://www.ncc.up.pt/yap/ • Visual Prolog (Turbo Prolog)‏ • http://www.visual-prolog.com/

  24. P-Phunck - Prolog Sources • Clocksin, W.F and Mellish, C.S. Programming in Prolog. Berlin. Springer-Verlag: 1984 • Sebesta, Robert W. Concepts of Programming Languages: Eighth Edition. 2007 • http://en.wikipedia.org/wiki/Prolog

More Related