Well... I don't even have a blog. But, I believe, size is a very good heuristic (i.e. the number of rules, the number of variables in rules, the number of bran

Well... I don't even have a blog. But, I believe, size is a very good heuristic (i.e. the number of rules, the number of variables in rules, the number of branches in rules). Another valuable metric to optimize is entropy. I.e. rules that look very similar aren't very good rules. Expressiveness: how long does the program have to be to capture a useful concept. Things like these obviously need a lot of counting and coming up with some kinds of constants, hopefully justified by experiments... That's a lot of work that will also require a lot of resources to do. But this is not to say that it is unknowable or that a programmer cannot develop an intuition which allows for rough assessment of language grammar. So, I'm sorry, I don't have a good answer... I only offer one based on my intuition and limited experience of dealing with various language grammars.