This is an example sketch that will be included with my next library (QScript).

This applet will accept a user defined function and display its graph between the low and high x values. There are 8 pre-defined graphs available but the fun is creating your own. (Summary of functions available can be found here)

Simply type in any expression as a function of $n (all variable names in QScript start with $) and click on the Draw button. If you make a mistake then an error message will appear in the red box and the offending part highlighted.

BTW The controls were created with G4P.

Have fun