%
% CS 430 Tower of Hanoi in Prolog
% From: http://www.cs.toronto.edu/~sheila/384/w11/simple-prolog-examples.html
%

% move(N,X,Y,Z) - move N disks from peg X to peg Y, with peg Z being the
%                 auxilliary peg
%
% Base Case: One disc - To transfer a stack consisting of 1 disc from
%            peg X to peg Y, simply move that disc from X to Y
%
% Recursive Case: To transfer n discs from X to Y, do the following:
%        Transfer the first n-1 discs to some other peg X
%        Move the last disc on X to Y
%        Transfer the n-1 discs from X to peg Y

move(1,X,Y,_) :-
    write('Move top disk from '),
    write(X),
    write(' to '),
    write(Y),
    nl.             % newline

move(N,X,Y,Z) :-
    N>1,
    M is N-1,
    move(M,X,Z,Y),
    move(1,X,Y,_),
    move(M,Z,Y,X).