Periodic function plotting

[Adir_Sh]

Hi.
I'm trying to plot a periodic function using my ti-89 titanium but I get a memory error.
I've defined the function as follows:

define f(x)=when(x<=x<pi,pi+x,f(x+pi))
graph f(x),x

Then it starts plotting the function, but the memory error appears before it completes the plotting.

Could you please tell me what am I doing wrong?

Thanks.