You selected mcpi.pl

/* Monte Carlo Simulation of Pi */
% 18 Nov 2002. modified: 19 Nov 2002.
:-write('%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%'),nl,
write(' A Monte Carlo Simulation of Pi'),nl,
write('%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%'),nl,
write('type sim_pi(mc_trial,1000,P). or so.'),nl.
mc_trial:-
% By `P is random(11)', with uniform probability,
% we get a value of P as an element of [0, ..., 10].
X is random(11) - 5,
Y is random(11) - 5,
Z is X^2 + Y^2,
update_counter,
(Z =< 25 -> update_pi;true).
update_pi:-
retract(pi(P)),
P1 is P + 1,%write(pi(P1)),
assert(pi(P1)).
update_counter:-
retract(n(N)),
N1 is N + 1,%write(n(N1)),
assert(n(N1)).
pi(0).
n(0).
n_init:-
abolish(sim_result,2),
abolish(pi,1),
abolish(n,1),
assert(pi(0)),
assert(n(0)).
sim_pi(_,N,abend):-
N > 1000,
write('It will go beyond the self-preservation. Please try a smaller.').
sim_pi(G,N,Pi):-
G=mc_trial,
N =< 1000,
n_init,
length(X,N),
forall(
nth1(K,X,_),
(
G,
sim_result(Pi),
assert(sim_result(K,Pi)),
trim_stacks
)
),
sim_result(N,Pi).
sim_result(Pi):-
pi(A),
n(N),
Pi is A * 400 / N.

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