Dependancies

Requires gprolog, which is available through a few different providers:

• On OSX, recommend Homebrew – brew install gnu-prolog

Demonstrations

Generating sets of change

Prolog will continue to generate solutions as long as ; is entered.

% gprolog --consult-file change.pl
| ?- change(100, H, Q, D, N, P).

H = 2
Q = 0
D = 0
N = 0
P = 0 ? ;

H = 1
Q = 2
D = 0
N = 0
P = 0 ? ;

H = 2
Q = 1
D = 2
N = 1
P = 0 ? ;

H = 1
Q = 1
D = 2
N = 0
P = 5 ?

yes

Counting number of solutions

Predicate bagof/3 accumulates results of the given predicate into a list, which can then be counted. Note that this is not particularly memory-efficient, and a custom implementation that does not store results will do better.

% gprolog --consult-file change.pl
| ?- bagof(R, change_set(100, R), B), length(B, N).

N = 292

(9ms) yes