Naive Parallel Factorial

factorial.erl

% Naive Parallel Factorial
% The second line defines the number of processes that will be spawned.
% Modify the number to control the task distribution.

-module(factorial).
-define(PROC, 4).
-export([sub_factorial/2, sub_factorial/3]).
-export([calculate/1, calculate/2]).

sub_factorial(V, N, PID) ->
	PID ! sub_factorial(V, N).
sub_factorial(V, N) when V =< N ->
	V*sub_factorial(V+?PROC,N);
sub_factorial(V, N) when V > N ->
	1.

calculate(N) ->
	PID = spawn(factorial,calculate,[?PROC, []]),
	Range = lists:seq(1,?PROC),
	[spawn(factorial,sub_factorial,[X, N, PID]) || X <- Range].
calculate(0, F) ->
	io:format("Calculating product ~n"),
	X = lists:foldl(fun(X,Prod) -> X*Prod end, 1, F),
	io:format("Fact Answer : ~p ~n",[X]),
	1;
calculate(C, F) ->
	receive
		X -> calculate(C-1, [X|F])
	end.