Quite a lot, actually. Polynomials can be easily manipulated, such as taking a derivative, and the result is still valid executable code. Macros use homoiconi

Quite a lot, actually. Polynomials can be easily manipulated, such as taking a derivative, and the result is still valid executable code. Macros use homoiconicity all the time, doing code walking and code expansion. Functions can construct and return functions easily.