Functional sets in C++

1_typedefs.cpp

typedef std::function<bool(int)> Set;
typedef std::function<bool(int)> Predicate;

2_singletonSet.cpp

Set singletonSet(int val) {
	return [=](int x){return x==val;} ;
}

3_union_and_intersection.cpp

Set set_union(Set s1, Set s2)
{
	return [=](int x){return contains(s1,x) || contains(s2,x);};
}

Set set_intersection(Set s1, Set s2)
{
	return [=](int x){return contains(s1,x) && contains(s2,x);};	
}

demo_intersection.cpp

void demo_intersection(void)
{
  Set s1=singletonSet(1);
  Set s2=singletonSet(2);
  Set s3=singletonSet(3);

  Set all=set_union(s1,set_union(s2,s3));
  Set s1b=set_intersection(all,s1); // back to s1, since it is the intersection of all=(s1 U s2 U s3)
  Set empty=set_intersection(s1,s2); // empty set ! why ?

  cout << contains(s1b,1) << endl; // what would this print and why?
}

demo_union.cpp

void demo_union(void)
{
  Set s1=singletonSet(1);
  Set s2=singletonSet(2);
  Set s3=singletonSet(3);

  Set un=set_union(s1,s2);
  Set all=set_union(s1,set_union(s2,s3));

  cout << contains(s1,2) << endl; // this should print 0 (meaning false :)
  cout << contains(s2,2) << endl; // this should print 1 (meaning true :)
  cout << contains(all,3) << endl; // this should print 1 (meaning true :)
}