Sorry if this is a stupid question, but this tournament looked to me like a thinly disguised version of:

"Construct a robot that can read code and interpret what it means."

which is a Really Hard Problem.

Is that not a fair description? Was there some other way to approach the problem?

The only way I can see to go about constructing a GOOD entrant to this is to write something that can take as its input the code of the opponent and interpret what it will actually DO, that can recognize the equivalence between (say):

return DEFECT

and

if 1: return DEFECT return COOPERATE

and can interpret things like:

if oppcode == mycode return COOPERATE return DEFECT

And I have no idea how to go about doing that. From the fact that the winning entrants were all random, it seems safe to say that no entrants had any idea how to go about doing that either.

Am I missing something here?