Expand description
A graph module for use in dataflow, region resolution, and elsewhere.
§Interface details
You customize the graph by specifying a “node data” type N and an
“edge data” type E. You can then later gain access (mutable or
immutable) to these “user-data” bits. Currently, you can only add
nodes or edges to the graph. You cannot remove or modify them once
added. This could be changed if we have a need.
§Implementation details
The main tricky thing about this code is the way that edges are
stored. The edges are stored in a central array, but they are also
threaded onto two linked lists for each node, one for incoming edges
and one for outgoing edges. Note that every edge is a member of some
incoming list and some outgoing list. Basically you can load the
first index of the linked list from the node data structures (the
field first_edge) and then, for each edge, load the next index from
the field next_edge). Each of those fields is an array that should
be indexed by the direction (see the type Direction).