Berbeda dengan bahasa pemrograman yang lain, yang menggunakan algoritma konvensionl sebagai teknik pencariannya seperti pada Delphi, Pascal, BASIC, COBOL dan bahasa pemrograman yang sejenisnya, maka prolog menggunakan teknik pencarian yang di sebut heuristik (heutistic) dengan menggunakan pohon logika.
Contohnya adalah pembuatan menara hanoi, dimana memindahkan sebuah balok atau N disk pada ujung kiri ke ujung kanan menggunakan perantara tengah tersebut. Dimana akhirnya akan sama dengan posisi semula. Contoh pada gambar adalah N=3 disk (balok).Source code :
- /****************************************************************/
- /* TOWERS OF HANOI */
- /* =============== */
- /* */
- /* Call the predicate hanoi with the number of discs, you want. */
- /****************************************************************/
- DOMAINS
- TIME, ROW, COL, NUMBER = INTEGER
- PREDICATES
- hanoi( NUMBER )
- move( NUMBER, NUMBER, ROW, ROW, ROW, COL, COL, COL )
- inform( NUMBER, NUMBER, ROW, ROW, COL, COL )
- makepole( NUMBER, NUMBER, COL)
- dd(TIME)
- move_vert(COL,NUMBER,ROW,ROW)
- move_horizon(ROW,NUMBER,COL,COL)
- keyact(CHAR)
- gendelay
- showdelay
- nondeterm for(INTEGER,INTEGER,INTEGER)
- fill
- DATABASE
- determ delay(INTEGER)
- CLAUSES
- for(X,X,_).
- for(I,A,B):-B>A,A1=A+1,for(I,A1,B).
- fill:- % fill current window.
- makewindow(_,_,_,_,_,_,ROWS,COLS),
- RR=ROWS-1, CC=COLS-1,
- for(COL,0,CC),for(ROW,0,RR),
- scr_char(ROW,COL,'°'),
- fail.
- fill.
- gendelay :- inkey(CH), keyact(CH),showdelay,!.
- gendelay :- delay(DELAY),!, dd(DELAY).
- gendelay.
- dd(0):-!.
- dd(N):-N1=N-1,dd(N1).
- keyact('+'):-
- retract(delay(VAL)),VAL1=VAL+1+VAL div 10,
- VAL1<=25000,!,assert(delay(VAL1)).
- keyact('+'):-!,assert(delay(25000)).
- keyact('-'):-
- retract(delay(VAL)),VAL1=VAL-1-VAL div 10,
- VAL1>=0,!,assert(delay(VAL1)).
- keyact('-'):-!,assert(delay(0)).
- keyact(_):-retractall(delay(_)),assert(delay(0)).
- showdelay:-
- delay(DELAY),gotowindow(2),
- clearwindow,
- write("Delay= ",DELAY),gotowindow(1).
- hanoi(N) :-
- N<=13,!,
- textmode(ROWS,COLS),
- makewindow(4,7,0,"",0,0,ROWS,COLS),
- fill,
- ROWS1=ROWS-1,
- makewindow(3,40,0,"",ROWS1,0,1,COLS),
- write(" + Improve delay, - Lower delay, Other keys removes delay"),
- VB=2+6*N,VH=3+N,CV=N, CM=3*N, CH=5*N,
- STCOL=(79-6*N) div 2, STROW=(25-VH) div 2 -1,
- STROW1=STROW+1+VH,
- makewindow(2,74,0,"DELAY",STROW1,34,1,13),
- makewindow(1,7,52,"Hanoi",STROW,STCOL,VH,VB),
- retractall(delay(_)),
- makepole(N,N,CV),
- assert(delay(100)),
- showdelay,
- move(N,N,0,0,0,CV,CM,CH),
- cursor(0,0), write("Press any key"),readchar(_).
- hanoi(_):- write("maximum 13 disc's\n").
- move(H,1,HA,_,HC,CA,_,CH):-!,inform(H,1,HA,HC,CA,CH).
- move(H,N,HA,HB,HC,CA,CB,CC):-
- N1=N-1,
- HA1=HA+1,
- move(H,N1,HA1,HC,HB,CA,CC,CB),
- inform(H,N,HA,HC,CA,CC),
- HC1=HC+1,
- move(H,N1,HB,HA,HC1,CB,CA,CC).
- inform( H, N, H1, H2, C1, C2 ) :-
- C11=C1-N, C22=C2-N, NN=2*N,
- H11=H-H1, H22=H-H2,
- move_vert(C11,NN,H11,1),
- move_horizon(1,NN,C11,C22),
- move_vert(C22,NN,1,H22).
- makepole(_,0,_):-!.
- makepole(H,N,C):-HH=H-N,inform(H,N,HH,HH,C,C), N1=N-1, makepole(H,N1,C).
- move_vert(_,_,H,H):-!.
- move_vert(COL,SIZE,H1,H2):-H1
- H11=H1+1,
- field_attr(H11,COL,SIZE,112),
- field_attr(H1,COL,SIZE,7),gendelay,gendelay,
- move_vert(COL,SIZE,H11,H2).
- move_vert(COL,SIZE,H1,H2):-H1>H2,!, /* move down */
- H11=H1-1,
- field_attr(H11,COL,SIZE,112),
- field_attr(H1,COL,SIZE,7),gendelay,gendelay,
- move_vert(COL,SIZE,H11,H2).
- move_horizon(_,_,H,H):-!.
- move_horizon(ROW,SIZE,C1,C2):-C1
- C11=C1+1, HH=C1+SIZE,
- field_attr(ROW,HH,1,112),
- field_attr(ROW,C1,1,7),gendelay,
- move_horizon(ROW,SIZE,C11,C2).
- move_horizon(ROW,SIZE,C1,C2):-C1>C2,!, /* move left */
- C11=C1-1, HH=C11+SIZE,
- field_attr(ROW,C11,1,112),
- field_attr(ROW,HH,1,7),gendelay,
- move_horizon(ROW,SIZE,C11,C2).
- GOAL hanoi(12).
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