Question

Is there a way to add individual labels when you specify a graph using the following format?

digraph {
    1 -> 2 -> 3 -> 1
}

Answer 1

If you mean labels on nodes, it can be done like this:

digraph { 
    1 [label="A"]
    2 [label="B"]
    3 [label="C"]
    1 -> 2 -> 3 -> 1 
 }

If you want to label the edges, you have to split them up like this:

digraph { 
    1 -> 2 [label="A"]
    2 -> 3 [label="B"]
    3 -> 1 [label="C"]
}

The reason you cannot do something like 1 -> 2 [label="x"] -> 3 [label="y"]... can be found in the dot specification:

attr_list   :   '[' [ a_list ] ']' [ attr_list ]
a_list  :   ID [ '=' ID ] [ ',' ] [ a_list ]
edge_stmt   :   (node_id | subgraph) edgeRHS [ attr_list ]
edgeRHS     :   edgeop (node_id | subgraph) [ edgeRHS ]

Each edge_stmt can have only one attr_list.