Compile-time calculation: Difference between revisions

</pre>

=={{header|Prolog}}==

For this, and many other complex calculations, goal_expansion/2 can be used.

goal_expansion/2 will change the goal in the code at compile time to be something else, in the case the constant number.

<lang Prolog>% Taken from RosettaCode Factorial page for Prolog

fact(X, 1) :- X<2.

fact(X, F) :- Y is X-1, fact(Y,Z), F is Z*X.

goal_expansion((X = factorial_of(N)), (X = F)) :- fact(N,F).

test :-

F = factorial_of(10),

format('!10 = ~p~n', F).</lang>

{{out}}

<pre>

?- test.

!10 = 3628800

true.

?- listing(test).

test :-

A=3628800,

format('!10 = ~p~n', A).