> In Lisp, you don't just write your program down toward the language, you also build the language up toward your program. As you're writing a program you may think "I wish Lisp had such-and-such an operator." So you go and write it. Afterward you realize that using the new operator would simplify the design of another part of the program, and so on.

That's close, but not quite the wording I remember, so I must have seen it somewhere else as well. That's a pretty good description of what I was referring to, though.

I was (re-)reading On Lisp yesterday and came across two further variations by pg:

In preface:

As well as writing their programs down toward the language, experienced Lisp programmers build the language up toward their programs.

Then later in 1.2 "Programming Bottom-up", pg rephrases that statement:

In Lisp, you don’t just write your program down toward the language, you also build the language up toward your program