We present in this paper SonicFunction, a prototype for the interactive sonification of mathematical functions. Since many approaches to represent mathematical functions as auditory graphs exist already, we introduce in SonicFunction three new aspects related to sound design. Firstly, SonicFunction features a hybrid approach of discrete and continuous sonification of the function values f(x). Secondly, the sonification includes information about the derivative of the function. Thirdly, SonicFunction includes information about the sign of the function value f(x) within the timbre of the sonification and leaves the auditory graph context free for an acoustic representation of the bounding box. We discuss SonicFunction within the context of existing function sonifications, and report the results from an evaluation of the program with 14 partially sighted and blind students.