/**
This actor implements the sieve of Eratosthenes.

@author JWJ
*/

actor PrimeSieve ()

            Integer Input ==> Integer Output:

  // Initialize the filter function to one that returns false:
  // the first token will always be let through.


  [Integer --> Boolean] filter := lambda (Integer a) --> Boolean : false end;

  function divides (Integer a, Integer b) --> Boolean :
    b mod a = 0
  end


  // Simply remove the token if the filter function returns true.

  action [a] ==> [] guard filter(a) end


  // Let the token through if the filter function returns false.

  action [a] ==> [a] guard not filter(a)
                     var [Integer --> Boolean] f = filter
  do
    // After saving the current filter function in f, create a new filter
    // that is the logical or of the previous one, and an application of the
    // predicate with the current token as the second argument.

    filter := lambda(Integer b) --> Boolean: f(b) or divides(a, b) end;
  end

end