This is way better than what I wrote. Thanks! Here's an example in concrete terms of the power of this technique: https://github.com/laarc/monki/blob/master/

This is way better than what I wrote. Thanks! Here's an example in concrete terms of the power of this technique: https://github.com/laarc/monki/blob/master/sudoarc.l https://github.com/laarc/monki/blob/master/sudoarc.l That's a file which adds many of Arc's constructs to Lumen: printing (pr, prn), list building (accum), structure (w/uniq, aif, awhen), etc. To put it another way: At the top of the file, the language available to you is Lumen. But at the bottom of the file, the language available to you resembles Arc. (It doesn't redefine anything from Lumen, though, so it's not a destructive change.) That must sound pretty dubious. It probably sounds like it's useful only for lone-wolf programmers rather than a team. If you give people the power to reshape the language, wouldn't it wreak havoc in a team setting? The answer turns out to be no, and it's surprising enough to write an essay about. Having macros available to your team ends up making your team more powerful, not less. It's simply a technique to generate patterns of code. When coupled with a good debugger, there's no mystery when things break. When an error happens, you get a debug breakpoint right where the error occurred. It makes no difference whether the error occurs during a macro expansion or during a function call, because macros are simply functions that answer "What should happen next?" It's like having a function that takes code as input and returns code as output, which is then executed. Except in Javascript, you'd have to do that by representing code as strings, which get passed to eval. In Lisp, code is a list. Meaning you can walk through it and see "This is an if statement. This is a function call." Etc. It's true that there are ways to abuse macros which make them difficult to understand or debug. But this is rare. The most common case is a short, simple transformation like d0m showed: "here is a pattern; please generate it."