Dan Drake dandrake

A macro that creates constants in Racket

Inspired by this Racket discourse post I tried writing a macro that defines bindings that work like constants in Racket.

Note that the solution here handles using set!; you can't prevent shadowing or redefining these variables -- see the Discourse thread.

If you run

#lang dtc/frames/animations
(animate `(1 2 3))

as a script from the command line in Ubuntu 25.04, the result is:

invalid memory reference. Some debugging context lost

You can write Markdown content and is should work as expected with links and such.

Moreoever, because this is github, there's git's revision control behind the scenes.

Here's a typo that I'll fix...click Edit in the top right, and edit away. Then see your changes in the Revisions tab from the upper left.

I even attached an image file: .

	#lang racket

	#\|

	I'm trying to understand parameters in Racket.

	One idea: for a recursive function,
	have a parameter that says how much to indent a debugging print
	statement so that I can see the call stack more clearly.

	#lang racket/base


	;; This is lovely but Exercism doesn't let you (require math)!
	;;
	;; Posted this: https://gist.github.com/dandrake/d9a3e20021a68ed16bce6f5dc79e62eb



	(require racket/contract)

	<!--

	You want to use your phone as a flashlight, but using the camera flash
	is (1) too bright, and (2) is white and is jarring at night if you want
	just a bit of dim light.

	So you want, say, a dim, red light.

	There are apps that turn your entire screen some color, but you don't
	need that. Just transfer this HTML page to your phone and load it up in

	#!/usr/bin/env racket

	;;;; Support code for my shell "gitcd" function: if you are in a git
	;;;; repo, but not in the worktree part -- you're in a regular repo
	;;;; somewhere inside the .git directory, or in a bare git repo -- the
	;;;; usual "git rev-parse --show-toplevel" stuff doesn't work.
	;;;;
	;;;; The code here detects those situations where rev-parse fails: it
	;;;; looks for either ".git" somewhere in the current directory's
	;;;; ancestry, or "reponame.git" in the cwd ancestry.

	;; Inspired by this blog post on "let's surround":
	;; https://arialdomartini.github.io/emacs-surround-2 and
	;; https://www.emacswiki.org/emacs/SurroundRegion.
	;;
	;; Notable bits:
	;;
	;; - Specifying =open= as a default value in the closing delimiter completing
	;; read -- that allows the user to hit return to re-use the opening
	;; delimiter for the closing one.
	;; - This moves point accordingly, so that you can make repeated calls to

	"""
	Print a "continuous" calendar -- as a ribbon / candy bar:
	https://davidseah.com/node/compact-calendar/

	https://docs.python.org/3/library/calendar.html

	Example output:

	>>> calendar.setfirstweekday(1)
	>>> print(domonths(2023, 9, 6))

	; Emacs has two mark rings: a buffer-local one, and a global one. I always get confused with them; my mental model
	; is that there ought to be just one mark ring. I want to implement that without trampling over the existing mark
	; ring stuff. Here's a first draft at doing so: I just add a hook so that anytime the mark is set, we append to
	; my own personal mark ring, and then I have a function that is basically a copy-and-paste of pop-to-mark-command.

	; This...seems to work? I am (1) stunned that it was so easy, and (2) suspcious that this ought to be unnecessary
	; if I really understand the mark rings and used them correctly.

	; Thanks to https://mathstodon.xyz/@[email protected] for pushing me to try this; see https://mathstodon.xyz/@[email protected]/109913166908490838
	; and my replies.