tutorials

Writing Racket Macros: define-syntax and phases

19 May 2023
tutorials
computer-science, macros, racket

There are a bunch of different ways of writing a macro in Racket. There are also some tricky things around phases to keep in mind. This is to help me keep them all straight. 3+1 ways to make a macro # This form: (define-syntax-rule (foo args ...) (use args ...)) is equivalent to: (define-syntax foo (syntax-rules () ([foo args ...] (use args ...)))) Which, is in turn equivalent to: (define-syntax foo (λ (stx) (syntax-case stx () [(gensymed-foo args . ...

Make an Emacs Buffer Open the Way You Want

27 Dec 2022
tutorials
emacs

Are you tired of having a particular buffer pop open in the wrong direction? Do you wish, for example, that the Racket REPL buffer showed up on the right in a vertical split, rather than below in a horizontal one? Look no further. I give you, display-buffer-alist: (add-to-list 'display-buffer-alist '("\\*Racket REPL </>\\*" (display-buffer-in-direction) (direction . right))) That little snippet will make sure when you hit C-c C-k inside of a racket-mode buffer, a REPL will pop up on the right-side instead of on the bottom. ...

Continuations—what are they?

17 Nov 2022
tutorials, featured
programming, programming-languages

I had a friend ask me what continuations are, and why they're useful. There's a ton of literature about continuations; this is just a simple example meant to showcase something small and hopefully grokkable. You will need to understand a little bit of Racket, but if you know any Scheme, that should be good enough. If you just want a quick primer, check out Learn X in Y minutes for Racket. ...

How to write a type checker/type inferrer with good error messages

27 Jul 2022
featured, tutorials
programming-languages, type-checking, computer-science

All the source for this may be found on my SourceHut repository. Synopsis # Experimental type checker/inferer for a simple lambda calculus Description # This is a type inference system for a little language. (Described below.) It uses a fusion of type inference algorithms from PLAI, ESP, and μKanren. (See Resources) Broadly speaking, our type inference engine works by: generating typing constraints from the program solving those constraints We’ll describe each of those in more detail. ...

Adding a Clock to the Tab-Bar in Emacs 28

20 Jul 2022
tutorials
emacs

Today I figured out how to add a tab-bar to Emacs. I didn’t like having it in the mode-line: it gets duplicated for every window and my mode-line space is precious. In contrast, the right side of the tab-bar was always blank.

microKanren Reading

4 Jul 2022
tutorials, featured
programming-languages, racket

μKanren (“micro-Kanren”) is a tiny, embeddable logic programming language. It’s easy to understand and implement in almost any language. It’s a great case study of an embedded language: unlike other common “embedded” languages like SQL or regex, which normally are represented as just plain-old strings, μKanren takes more advantage of the host language’s features. I recommend reading the original paper: it’s short, well-written, and easy to understand. I did a write-up which you can read on Sourcehut. ...

FreeBSD on a Raspberry Pi 4 with 4GB of RAM

28 Dec 2020
tutorials
raspberry-pi, freebsd

This is the story of how I managed to get FreeBSD running on a Raspberry Pi 4 with 4GB of RAM, though I think the setup story is pretty similar for those with 2GB and 8GB.1

I also managed to get Rust built from source, (kind of) which is nice because the default Rust installer doesn’t seem to work for FreeBSD running on a Raspberry Pi.

...

FreeBSD on a Raspberry Pi

12 Feb 2020
tutorials
freebsd, tools

I’m a FreeBSD guy. My first computer was a FreeBSD machine that my dad had running in a closet. I learned how to use Emacs as well as the command line on that black-screen white-text no-mouse interface. That’s how real programmers spend their childhood! 😎 😜 I’ve only heard good things about FreeBSD. While not known as particularly desktop-friendly (various Linux distros win here) I’ve heard tales of its rock-solid stability. ...

Citations with Pandoc

6 Feb 2019
tutorials
tools, writing

Today I figured out how to get Pandoc to automatically generate MLA citations for me! I used Pandoc and the Biblatex bibliography format. What’s nice about this is that you can enter in all the information you know about the source, keep it nice and organized in a file, and then change the citation style on the fly. Imagine if you thought you had to use MLA, but then realized you needed to switch to APA citation styles. ...

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