//
// set_union.pp
// 
// The following propagation patterns allow for the use of Vertex_comma_lists
// as sets in the set-theoretic sense.  There are two variants of the 
// set_union function.
// 
// set_union(Vertex* w) takes a vertex w and adds it to the list if it is not
// already in the list.
// 
// set_union(Vertex_comma_list *l) takes a list of vertices.  Each vertex in 
// the list l is added to the list if it is not already in the list.  This is 
// easier to implement in propagation patterns if the list of vertices to be 
// added is the object being traversed, however, this is not syntactically 
// consistent with the set_union above.  To preserve readability in the rest 
// of the code and to ease implementation this is done with two operations.  
// One takes the syntax one would expect then swaps the lists and calls the 
// version that is easier to implement.
// 
// Both functions assume that the list being added to is already a set.
// 

// add Vertex* w to the Vertex_comma_list if it is not already in the list
*operation* void set_union(Vertex* w)
  *traverse* *from* Vertex_comma_list *to* Vertex
  *carry* *inout* int in_list = (@ 0 @)
    *along* *from* Vertex_comma_list *to* Vertex
  *wrapper* Vertex_comma_list
    *suffix* (@ if (!in_list) { this->append(w); } @)
  *wrapper* Vertex
    *prefix* (@ if (g_equal(w)) { in_list = 1; } @)


// add each Vertex in the Vertex_comma_list* l to the Vertex_comma_list if 
// it is not already in the list
*operation* void set_union(Vertex_comma_list* l)
  *traverse* *from* Vertex_comma_list *to-stop* Vertex_comma_list
  *wrapper* Vertex_comma_list
    *prefix* (@ l->set_union_swap(this); @)

*operation* void set_union_swap(Vertex_comma_list* final_list)
  *traverse* *from* Vertex_comma_list *to* Vertex
  *wrapper* Vertex
    *prefix* (@ final_list->set_union(this); @)