Pure functional languages, for example, could easily be represented graphically. Functions are black boxes with inputs and outputs and some transformation taking place inside, which is composed of a combination of other functions and primitive operations. Imperative languages (what most people use) could also be represented graphically, but it wouldn't be as simple as functional languages. I don't have any very specific ideas, but I do know that there are always people working on these kind of things. Hopefully something will gain traction soon.