draw() allows the program to loop. Without it, the program simply stops executing but the window remains open.
See http://processing.org/reference/draw_.html, specifically this sentence:

draw() must exist if you want the code to run continuously or to process events such as mousePressed().

It is a well known limitation, and I don't see why you don't want to add draw().
It can be empty, you can add noLoop() to setup(), but it must be there.

Hi all,
I wasn't aware that the keypress related events were dependent on the presence of the draw() function - I'm guessing that the creation of Java's KeyListener is dependent on draw().  I was experimenting with calling different drawing routines programmatically and decided to add in a key-driven switch and was surprised to see that it didn't work.

On multiple occasions I've created programs that have no draw() in them  - why add something that you have no intention of using.
The one thing they all had in common was that they were all non-interactive, ie no mouse and no keyboard inputs. They were just doing simple data visualization.

Phi.lho - if you put noLoop() in setup(), keyboard reading also fails. Evidentally in order for the keyboard to be read, the draw() must be actively looping.

Best Regards, Jim

Yeah- the mouse and keyboard inputs are queued up until they have a chance to execute in draw(), either before or after, I'm not sure.

Yes, I agree this behavior can be surprising, and maybe should be better documented.
And I tested the noLoop() before answering, but stupidly I tested it with mousePressed(), which doesn't need draw() at all... (I thought the behavior was the same for both kind of events.)