Sunday, September 30, 2007

Rewriting Software, Part 2

When I wrote my previous post about rewriting software, I had a couple of simple goals in mind. First was answering Ovid’s question on when rewriting software is wise, and when it is foolish. Second was to re-examine Joel Spolsky’s dictum, never rewrite software from scratch, and show how software is so complex that no one answer fits all circumstances. Finally, I wanted to highlight that there are many contexts to examine, ranging from the “small here and short now” to the “big here and long now” (to use Brian Eno’s terminology).

When I wrote that post, I though there would be enough material for two or three followup posts that would meander around the theme of “yes, it’s OK to rewrite software”, and move on. The more I wrote, the more I found to write about, and the longer it took to condense that material into something worth reading.

Rather than post long rambling screeds on the benefits of rewriting software, I decided to take some time to plan out a small series of articles, each limited to a few points. Unfortunately, I got distracted and I haven’t posted any material to this blog in over a month. My apologies to you, dear reader.

Of course, there’s something poetic about writing a blog post about rewriting software, and finishing about a month late because I couldn’t stop rewriting my post. There’s a lesson to learn here, also from Joel Spolsky. His essay Fire and Motion is certainly worth reading in times like these. I try to re-read it, or at least recall his lessons, whenever I get stuck in a quagmire and can’t see my way out.

In that spirit, here’s a small nugget to ponder.

If you are a writer, or have ever taken a writing class, you’ve probably come across John R. Trimble’s assertion that “all writing is rewriting.” Isn’t it funny that software is something developers write yet fear rewriting?

There’s a deep seated prejudice in this industry against taking a working piece of software and tinkering with it, except when it involves fixing a bug or adding a feature. It doesn’t matter if we’re talking about some small-scale refactoring, rewriting an entire project from scratch, or something in between. The prejudice probably comes from engineering — there’s no good reason to take a working watch or an engine apart because it looks “ugly” and you want to make it more “elegant.”

Software sits at the intersection of writing and engineering. Unlike pure writing, there are times when rewriting software is simply a bad idea. Unlike pure engineering, there are times when it is necessary and worthwhile to rewrite working code.

As Abelson and Sussman point out, “programs must be written for people to read, and only incidentally for machines to execute.” Rewriting software is necessary to keep code concise and easy to understand. Rewriting software to follow the herd or track the latest trend is pointless and a wasted effort.

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