Hi Mira:

Is the following a convenient set of primitives for visitor entries?

A

|      on-entering    ->A,b,B
|
|
|      when-visiting  ->A,b,B
|
|
V      on-exiting     ->A,b,B

       on-entering    B
B      when-visiting  B
       on-exiting     B

start s (@ ... @)
during s { any of the above }
finish s (@ ... @)

Your example slightly modified:

GenericDFTVisitor(Strategy s:
  {-> Graph Adjacency stop
   -> Adjacency Vertex
   -> Vertex Adjacency}
   Adjacency {
     boolean mark;
     return (@ mark @)
     on-entering (@ if (mark==false) {mark=true;}; @)
   }

ConnectivityVisitor modifies GenericDFTVisitor{
  Integer count;
  return (@ count @)
  during {-> Graph Adjacency stop} { 
    Adjacency {
      on-entering (@ 
	if (next.return()=false)
	  // check whether unmarked
	  {count+=1; next()};@)}}}


-- Karl