fib.pl

#!/usr/bin/gprolog --consult-file

fib(1, 1).
fib(2, 1).
fib(N, R) :- N1 is N-1, fib(N1, R1), N2 is N-2, fib(N2, R2), !,  R is R1 + R2.

friends.pl

#!/usr/bin/gprolog --consult-file
likes(wallace, cheese).
likes(grommit, cheese).
likes(wendolene, sheep).

friend(X, Y) :- \+(X == Y), likes(X, Z), likes(Y, Z).

hanoi.pl

#!/usr/bin/gprolog --consult-file

hanoi(1, From, _, To) :-
  write(From),
  write(' -> '),
  write(To),
  nl.

hanoi(N, From, Via, To) :-
  N > 1,
  M is N-1,
  hanoi(M, From, To, Via),
  hanoi(1, From, _, To),
  hanoi(M, Via, From, To).

minimum.pl

#!/usr/bin/gprolog --consult-file

my_minimum([X], X).
my_minimum([X|Xr], X) :-
  my_minimum(Xr, Y),
  Y >= X.
my_minimum([X|Xr], Y) :-
  my_minimum(Xr, Y),
  Y < X.

queens.pl

#!/usr/bin/gprolog --consult-file

valid_queen((_, Col)) :- member(Col, [1,2,3,4,5,6,7,8]).

valid_board([]).
valid_board([Head|Tail]) :- valid_queen(Head), valid_board(Tail).

cols([], []).
cols([(_, Col)|QueensTail], [Col|ColsTail]) :-
  cols(QueensTail, ColsTail).

diags1([], []).
diags1([(Row, Col)|QueensTail], [Diagonal1|DiagonalsTail]) :-
  Diagonal1 is Col - Row,
  diags1(QueensTail, DiagonalsTail).

diags2([], []).
diags2([(Row, Col)|QueensTail], [Diagonal2|DiagonalsTail]) :-
  Diagonal2 is Col + Row,
  diags2(QueensTail, DiagonalsTail).

eight_queens(Board) :-
  Board = [(1, _), (2, _), (3, _), (4, _), (5, _), (6, _), (7, _), (8, _)],
  valid_board(Board),

  cols(Board, Cols),
  diags1(Board, Diags1),
  diags2(Board, Diags2),

  fd_all_different(Cols),
  fd_all_different(Diags1),
  fd_all_different(Diags2).

reverse.pl

#!/usr/bin/gprolog --consult-file

my_reverse([], []).
my_reverse([X], [X]).
my_reverse([X|Xr], Ys) :-
  my_reverse(Xr, RevXr),
  append(RevXr, [X], Ys).

sort.pl

#!/usr/bin/gprolog --consult-file

lesser([], _, []).
lesser([X|Xr], Y, [X|Zs]) :-
  X < Y,
  lesser(Xr, Y, Zs).
lesser([X|Xr], Y, Zs) :-
  X >= Y,
  lesser(Xr, Y, Zs).

greater([], _, []).
greater([X|Xr], Y, [X|Zs]) :-
  X >= Y,
  greater(Xr, Y, Zs).
greater([X|Xr], Y, Zs) :-
  Y > X,
  greater(Xr, Y, Zs).

my_sort([], []).
my_sort([X], [X]).
my_sort([X|Xr], Rs) :-
  lesser(Xr, X, Lesser),
  greater(Xr, X, Greater),
  my_sort(Lesser, SortedLesser),
  my_sort(Greater, SortedGreater),
  append(SortedLesser, [X], R),
  append(R, SortedGreater, Rs).

sudoku.pl

#!/usr/bin/gprolog --consult-file

valid([]).
valid([Head|Tail]) :-
  fd_all_different(Head),
  valid(Tail).

print_puzzle([S11, S12, S13, S14,
              S21, S22, S23, S24,
              S31, S32, S33, S34,
              S41, S42, S43, S44]) :-
                print([S11, S12, S13, S14]),
                print('\n'),
                print([S21, S22, S23, S24]),
                print('\n'),
                print([S31, S32, S33, S34]),
                print('\n'),
                print([S41, S42, S43, S44]),
                print('\n').

sudoku(Puzzle, Solution) :-
  Solution = Puzzle,

  Puzzle = [S11, S12, S13, S14,
            S21, S22, S23, S24,
            S31, S32, S33, S34,
            S41, S42, S43, S44],

  fd_domain(Solution, 1, 4),

  Row1 = [S11, S12, S13, S14],
  Row2 = [S21, S22, S23, S24],
  Row3 = [S31, S32, S33, S34],
  Row4 = [S41, S42, S43, S44],

  Col1 = [S11, S21, S31, S41],
  Col2 = [S12, S22, S32, S42],
  Col3 = [S13, S23, S33, S43],
  Col4 = [S14, S24, S34, S44],

  Square1 = [S11, S12, S21, S22],
  Square2 = [S13, S14, S23, S24],
  Square3 = [S31, S32, S33, S34],
  Square4 = [S41, S42, S43, S44],

  valid([Row1, Row2, Row3, Row4,
         Col1, Col2, Col3, Col4,
         Square1, Square2, Square3, Square4]),
  print_puzzle(Solution).

sudoku2.pl

#!/usr/bin/gprolog --consult-file

valid([]).
valid([Head|Tail]) :-
  fd_all_different(Head),
  valid(Tail).

sudoku(Puzzle, Solution) :-
  Solution = Puzzle,

  Puzzle = [S11, S12, S13, S14, S15, S16,
            S21, S22, S23, S24, S25, S26,
            S31, S32, S33, S34, S35, S36,
            S41, S42, S43, S44, S45, S46,
            S51, S52, S53, S54, S55, S56,
            S61, S62, S63, S64, S65, S66],

  fd_domain(Solution, 1, 6),

  Row1 = [S11, S12, S13, S14, S15, S16],
  Row2 = [S21, S22, S23, S24, S25, S26],
  Row3 = [S31, S32, S33, S34, S35, S36],
  Row4 = [S41, S42, S43, S44, S45, S46],
  Row5 = [S51, S52, S53, S54, S55, S56],
  Row6 = [S61, S62, S63, S64, S65, S66],

  Col1 = [S11, S21, S31, S41, S51, S61],
  Col2 = [S12, S22, S32, S42, S52, S62],
  Col3 = [S13, S23, S33, S43, S53, S63],
  Col4 = [S14, S24, S34, S44, S54, S64],
  Col5 = [S15, S25, S35, S45, S55, S65],
  Col6 = [S16, S26, S36, S46, S56, S66],

  Square1 = [S11, S12, S13, S21, S22, S23],
  Square2 = [S14, S15, S16, S24, S25, S26],
  Square3 = [S31, S32, S33, S41, S42, S43],
  Square4 = [S34, S35, S36, S44, S45, S46],
  Square5 = [S51, S52, S53, S61, S62, S63],
  Square6 = [S54, S55, S56, S64, S65, S66],

  valid([Row1, Row2, Row3, Row4, Row5, Row6,
         Col1, Col2, Col3, Col4, Col5, Col6,
         Square1, Square2, Square3, Square4, Square5, Square6]).