In Matlab, how to refer a self-defined function in another self-defined function?

Dear all,

I have a question on Matlab: when I define a new function in Matlab, I want to use another function defined by myself previously as an input argument, how can I do that?

To be more specific, suppose I have defined a function, say f(x). Now I am going to define a new function g(x)=f(x)+x and using f(x) as one of the input argument in my definition of g(x).

Is there anybody who can help me on this? Thanks a lot in advance.