Wednesday, June 05, 2013

define vs attach

Racket’s macro system gives macros two ways of associating static (or compile-time) information with a particular name. One way is to define the name as the static information; the other is to attach the information to the already-defined name.

Friday, March 16, 2012

avoid flushing your wire protocol's performance down the pipes

When implementing a wire protocol, one occasionally needs to know something about the wires. This blog post is the story of how the placement of a call to flush-output caused a factor-of-20 variation in performance.

Thursday, February 09, 2012

unprepared queries vs statement caching

Racket’s db library supports parameterized queries where the SQL is given as a string (that is, unprepared):

(query-list c "SELECT field1 FROM table WHERE field2 = ?" 17)

This is handled by an implicit call to prepare, which turns the string into a prepared statement; the prepared statement is then executed with the arguments.

The problem with this approach is that it involves two trips to the server: one to prepare and one to execute. One trip would be better. In this post I discuss two techniques for eliminating extraneous server trips. I’ve recently added one of them to Racket; the other turns out to be problematic.

Monday, October 31, 2011

in praise of PostgreSQL arrays

I just added support for PostgreSQL arrays to the db library. While there are some uses of arrays that are iffy from a database design standpoint, there’s one use that weighs overwhelmingly in their favor: avoiding dynamic generation of SQL IN comparisons.

Sunday, October 16, 2011

lazy module loading

The Racket module system is good at managing dependencies. When you require a module, you ensure that that module is initialized before your code runs, and when the other module changes, the compiler will notice and recompile your module too. Racket even stratifies dependencies according to phase levels so you can use some modules in your macro implementations and other modules in your run-time code and the expander/compiler/linker knows what you want when. It keeps track and makes sure that everything is loaded and available when it’s supposed to be.

But sometimes you want to manage dependencies yourself. This post is about how to lazily load the implementations of functions and—with a bit of care—even macros.

Tuesday, September 27, 2011

definitions vs enclosing binding forms

There are two kinds of binding forms in Racket: definitions and enclosing binding forms. The scope of a binding introduced by an enclosing binding form is entirely evident: it’s one (or more) of the form’s sub-terms. For example, in

(lambda (var ...) body)

the scope of the var bindings is body. In contrast, the scope of a definition is determined by its context: the enclosing lambda body, for example, or the enclosing module—except that scope is too simple a term for how bindings work in such contexts. Enclosing binding forms are simpler and cleaner but weaker; definition forms are more powerful, but have a more complicated binding structure. Definitions also have the pleasant property of reducing rightward code drift.