Destructuring lists with match

:: Racket

Let’s say you need to destructure a list with match, using a pattern that specifies a “rest” or “more” element. Be careful. You probably want to use list* not list.

Does your Racket project need a makefile?

:: Racket, racket-cookbook

Most of my Racket projects don’t use a makefile. Why would they? raco make or raco setup suffices.

But a makefile can consistently define some common project tasks. And it can really help when you want to generate HTML documentation from Scribble sources, and publish it to GitHub Pages using the automagical gh-pages branch.1

__FILE__ and __LINE__ in Racket

:: Racket, racket-cookbook

Many languages have a variable (or preprocessor macro) called __FILE__ or __file__ whose value is the pathname of the current source file. Likewise __LINE__ for the the source line number.

You probably need this less in Racket than you imagine. For example:

  • We wouldn’t test that __FILE__ ends in main.rkt; instead we’d use a main submodule (module+ main <your code here>).

  • To get a data file foo.dat located in the same directory as a source file we’d use (define-runtime-path foo.dat "foo.dat"). If we’re a package or executable this works regardless of where our files happen to get installed.

But if you really did need a __FILE__ in Racket, how would you do it?

Racket cookbook

:: Racket, racket-cookbook

Two parallel thoughts:

  1. I haven’t blogged in awhile. I’ve been heads-down on a few projects. Plus I haven’t had ideas I feel are “big” or unique enough to merit a post.

  2. It’s occurred to me that a “Racket Cookbook” might be a useful resource. Because examples. Because real-life, practical examples.1

Although I haven’t created a cookbook, my working assumption is that it would be better to write one recipe at a time. As they arise. As I think, “Ah right, this wasn’t obvious to me when I was learning Racket.”

So I plan to experiment with releasing the things one at a time, as short blog posts. Thereby terminating two avian organisms with one geologic projectile.

Not sure if I’ll keep it up. Definitely not sure if I’ll ever collect and polish them into a “book” of some form. They might only ever live as a racket-cookbook tag on this blog.

  1. Admittedly I rarely recall using any “cookbook” resource to find the answer to a problem I have. Taken literally, programming cookbooks are largely a failure, for me. On the other hand, flipping through one can give the “flavor” of a language. And as I’ve written, one valid learning strategy is to absorb things shallowly — you may not know the answer, but you know roughly where to find the answer. It rings a bell. Probably cookbooks fit that model — filling your head with, um, bells. 

Using syntax/loc and unit test macros

:: Racket, racket-cookbook, macros

In my previous post, I wrote about a nuance with syntax/loc, using the example of a macro that both defines and provides a function. But why don’t I back up, and look at a simpler example of why you’d want to use syntax/loc. The example is a simple macro you might often find yourself wanting, to reduce the tedium of writing unit test cases.

Using syntax/loc

:: Racket, macros

There’s a nuance to syntax/loc. The documentation says, emphasis mine:

Like syntax, except that the immediate resulting syntax object takes its source-location information from the result of stx-expr (which must produce a syntax object), unless the template is just a pattern variable, or both the source and position of stx-expr are #f.

What does “immediate” mean here?

Racket package management

:: Racket

Racket’s new package manager is great. It debuted with Racket 5.3.5. Although officially still in beta, it was already good enough to use for real projects. Racket developers wanted people to use it for real projects, to get the experience needed to make it even better.

Over many months, the Git HEAD version of Racket — what would become Racket 6 — gradually introduced a few new and changed features for package management.

However, you might not want to use the newer features, yet. Not if you want your package to be usable by people still using Racket 5.3.5 or 5.3.6 — or usable by other packages that wish to support such people.

Fortunately, the older features are still supported in Racket 6, and it’s not very difficult or inconvenient to use them. You just need to know what they are.

Interview and RacketCon talk

:: software

I haven’t posted here in awhile because I’ve been busy with a variety of things in September, including an interview for IEEE Computer magazine and a talk about Frog at RacketCon. And I’m writing this in Japan.