#langs that Fit In Your Head

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2025-01-19 00:30:04

This post was written for Day 8 of the Racket Advent Calendar. “#lang” is a Racket term referring to declaring the programming language in use, and this post uses Racket as a platform to discuss one approach to writing good programming languages. I’ve made an effort to explain the Racket-specific ideas as they are introduced, so if you are interested in language design but aren’t a Racketeer, I hope you’ll still read it and that you’ll find it interesting.

When a way of expressing a complex idea becomes small enough to fit in your head and doesn’t require special effort on your part to remember, it has, in a useful sense, become a language.

Take Racket’s module system, for example (which, just like those of other languages, allows you to group source code into units typically contained in files). By just writing “require” (like python’s import), we gain the ability to describe with great and effortless nuance in just what manner we mean to include those modules — whether to retain the names of the included definitions or change them in some particular way, or include or exclude particular definitions, and more. And these various ways are composable, so we could do, without any fuss:

Of course we can do all these things. There’s no need to look up docs. This language fits in your head, and it expresses everything you might want to do when requiring modules. As Racketeers know, it’s hard to go back to other languages once you’ve been spoiled by Racket’s incredible module system!