DAG finished, Interpreter next.

I've fixed up a problem or two with my DAG implementation, and uploaded it to the cheeseshop. It must be one of the smallest packages ever! :-)

While writing some tests to make sure my traversal function was processing nodes in the desired order, I realised that traversing the graph results in a 1D list of nodes (processing instructions) with a bunch of stack pops and pushes in the right places. Then I realised... this list is never going to change, unless I add or remove nodes, which in practice, rarely happens.

This makes the DAG really only one phase of process, which can be re-visited as needed, not on every processing pass. The DAG is used to produce a linear list of instructions, which I can feed into an interpreter.

This sounds like a good optimisation to me, and a fun diversion for a Saturday afternoon.