Why On Lisp

The title is intended to stress the importance of bottom-up programming in Lisp. Instead of just writing your program in Lisp, you can write your own language on Lisp, and write your program in that.

It is possible to write programs bottom-up in any language, but Lisp is the most natural vehicle for this style of programming. In Lisp, bottom-up design is not a special technique reserved for unusually large or difficult programs. Any substantial program will be written partly in this style. Lisp was meant from the start to be an extensible language. The language itself is mostly a collection of Lisp functions, no different from the ones you define yourself. What’s more, Lisp functions can be expressed as lists, which are Lisp data structures. This means you can write Lisp functions which generate Lisp code.