Oliver Steele

A vice grip is the wrong tool for every job. — anonymous

Type declarations aren’t the best tool for any particular purpose, but they’re a passable tool for a lot of different purposes, and therefore they’re often the best tool for meeting several purposes at once. There are better ways to comment a program, to add metadata for tools and libraries, or to verify program correctness; but type declarations, in many languages, are a passable way to do all of these jobs at once.

The situation is similar to that of a convergence device such as a camera phone. The voice quality on my camera phone isn’t that great (the speaker shares a tiny clamshell lid with the camera optics and CCD), and the camera doesn’t take great pictures (the lens is smaller than a halfpenny), but I’d rather carry one substandard device than two separate best-of-breeds — even if I have to go get my “real” camera when it’s worth taking a good photograph. You can make the same argument for a PDA phone versus a laptop. And I believe the same holds for type declarations, versus all the mechanisms that, considered separately, are superior to them.

Last weekend, I shared some interesting properties of numbers with my kids.

The great thing about explaining something to a non-expert is that you have to actually understand the topic. (This is why making teaching universities and research universities the same actually makes sense.) If you hide behind a formalism, the explanation won’t work. Usually, this means that you didn’t understand why the formalism worked either.

This is why I thought “why are far away things smaller?” was such a great question. “Similar triangles” answers are brittle, and if a tiny error makes far away things come out bigger instead, you won’t catch yourself until you got to the end of the proof.

[Update 2006: “Model N” never caught on. A few months after I wrote this, Jesse James Garrett coined the term AJAX. This is what the architecture described in this post is known as today.]

In a traditional server-side web application, the server renders a series of views which are downloaded, as HTML, to the client. A client-side web application is an application that is deployed from a server and displays data from a server, but can render a series of views on the client.

I’ve been watching server-side developers try to figure out how to serve client-side web applications for a few years now. Different developers, that is — it doesn’t take years for any individual developer to figure it out. There’s often an initial stumble, which is caused by a mismatch between the obvious way to deploy a client-side web application, and the right way. The right way is simpler, but elusive.