I don't know what ABEL looks like. Just for grins, though, let's imagine a program that accepted as input a simple list of state transitions. Each entry in the list would include the initial state, the event that triggers that particular state transition, an (optional?) action to perform during the transition, and the ending state. I think that should be enough information to draw the state diagram.

Assuming that the diagram took the form of circles (representing the states) connected by arrows (representing the transitions among them), probably about the best a program could do automatically would be to arrange the circles in a way that minimized the lengths and/or crossings of the transition arrows. As you suggested, some additional hints in the input file might be needed to also produce a diagram that "made sense".

The arrangement of the various symbols on a flowchart is pretty much dictated by the structure of the pseudocode. Trying to automate the placement of the states on a state diagram seems like a much more open-ended problem to me. Interesting to think about, though.

-- Russ