Useimmat esimerkit on koodattu PDC-Prologilla (entinen Visual Prolog, entinen Turbo Prolog). PDC-Prologissa on PREDICATES-osiossa määriteltävä minkä tyyppisia argumentteja prediakaatit ottavat. DOMAINS-osiossa voi määritellä uusia tyyppejä sisäänrakennettujen tyyppien lisäksi. Sisäänrakennettuja tyyppejä ovat INTEGER, REAL, CHAR, STRING.
Esimerkkit voi ajaa ei-tyypitetyillä Prologeilla kommentoimalla määrittelyt pois.
Homework series 1 problem 3 this autumn 2005 was that of constructing program for solving Sudoku -problems. The 9X9 table must be filled with numbers between 1 and 9, so that each row , each column and each of the 9 3X3 -subtables was not a same number twice.
Here a solution which selects an entry in the table with unknown value which has a number of available values which is not larger than a value of some other field is presented.
Lots of improvements in the Sudoku-search process could be still made. One could think of maintaining the sets of available values more persistently instead of calculating them at each level anew.
The example can be run by calling the predicate:
sudoku(+Percentage_shown, +Subtable_dimension).
With 50 % the procedure seldom needs to backtrack. At 30% some problems are really difficult. For 9X9 the Subtable_dimension is 3. So start trials with sudoku(50,3). Remember that the program first forms satisfiable tables and only then hides required portion of the cells. The problem of deciding if a partially shown table has solutions is an other category not covered by this program. Fowever if the solver part would receive such it would in principle after some exchaustive search say "No".
And what were the lessons of this exercise? Basic data structure manipulations, search and backtracking, solution accumulation were practised. Also this could act as a bridge to the CLP-part of the course.
Program 16.3 in Chapter 16 (p. 304) of Sterling & Shapiro has caused some questions. Hopefully this code, comments and execution log will ease understanding.
See Mark Wallace paper in the material for the light meal example , here is the code (uses clpq).
Ask for lightmeal(Appetizer, Main, Dessert).