As a fledgling CL programmer, I've found macros to be one of its most enduring charms. Yet it is also one of its most criticized (or at least feared) features. Much like threads have become the bogeyman of the programming world, so macros would be too, if more than a handful of programmers actually knew about them. Among this handful, though, it would be nice to dispel the myth that macros are too powerful.
I mean, obviously, they are, in some sense, too powerful. The common complaint about them is that junior programmers (especially) can create what appear to be language-level constructs that confuse the heck out of everyone else, impairing the code's "readability". As with most broadly-accepted maxims (in this case, broadly accepted by the 15 people in the world who actually know about the issue in the first place), it is both well-intended, intuitively reasonable, and incorrect, for the simple reason that if, at your company, junior programmers are running amok with no mentors to teach them, the code will be unreadable whether or not it uses macros.
Frankly, I'd like to dispel the whole myth that there's great import to be placed on the "readability" of a programming language. I see blog after blog, each about as scientifically sound as my 10th grade Chemistry report (in case you're wondering, I'm not a chemist), about whether Perl is more readable than C, or vice-versa, or whether Python is more readable than CL, etc. This tiresome, endless debate stirs the fanboy in all of us, but is missing not just the forest for the trees, but the solar system for the planet.
I've read a lot of code in my day, I'll have you know. What matters most to readability is, first, comments, followed by identifier names, followed by there being as little code as possible, followed by program structure. Ok, I can hear the chorus of "boos" in the background at the preceding statement. All I can say is, most programmers have no idea how to write good comments (even though, as they say, the "force" is with them; they just have no idea, and lack a Yoda-like figure to explain it to them). When comments are good, there is nothing quite like it. The code could be written in TECO for all I care. Maybe blog, will I, about it, some day.
So macros, in fact, cannot really get in the way of readability. In fact, they have the potential to greatly enhance readability, used judiciously (and as pointed out earlier, if your company is not run judiciously, you have larger issues to work out first). How many of you out there have worked somewhere that had some kind of coding guidelines? I'd warrant that a fair number of you have. I certainly have. I'm talking about stuff like Ellemtel's Programming in C++, Rules and Recommendations.
Give those rules a once-over, if you haven't already. It's pretty complicated stuff. Use this feature this way, use that feature that other way, don't do this, do do that, etc, etc. Yawn. I've worked at companies that successfully enforced such rules (at least 80% of the time), and some that failed utterly. In both cases, it was wickedly hard to enforce these rules (successfully or not). All programmers had to read the coding guidelines document, understand it, remember it, and periodically re-read it when it was updated. Senior programmers had to enforce the guidelines during code reviews (which was sometimes easier than other times, depending on the stubbornness of the reviewee).
At more sophisticated shops, one could imagine, at least, that some of the rules would be enforced by build scripts. A poor solution if ever there was one. For one thing, build scripts tend to be written in a different language (e.g., Perl), and usually resort to crude regexp-matching in order to catch offending code. Only a handful of programmers at your company are brave (or foolish) enough to grok the build scripts. These poor souls find themselves, before too long, at the bottom of a pit of despair from which they never return (save by leaving for another team or company). Eventually they label themselves with self-deprecating monikers such as "build bitch".
Macros afford the possibility, at least, that some of these conventions be enforced within the language itself, rather than by a bunch of hacky Perl scripts (or no automated process at all). Take, for instance, the use of CL's DEFCLASS. Now DEFCLASS has roughly one grillion options for how to do this, that, or the other thing. It's also remarkably lax about, well, almost everything. If you want a member variable ("slot") called FOO but wish for the accessor to it to be called BAR, you can do that.
If you wanted to prevent such wanton creativity on the part of your less-trustworthy programmers, you could do so by writing a macro wrapping DEFCLASS which might both limit its complexity and enforce constraints such as the regular naming of accessors and the like. You could prevent the use of multiple inheritance if you found it too frightening (I'm not suggesting you go out and do this, just pointing out that you could). These rules would be enforce using code written in the same language as everything else, making them easier to write (in that they can harness the reflective power of the language itself, i.e., no hack regexps) and easier to find volunteers to maintain and develop.
I could go on and on about this, but it's getting late so I'll just wrap it up there. One last thing, though, I urge the readers of this blog (all three of you) to re-evaluate the various maxims you may have assimilated over the years. Are threads really that bad if there is a problem facing you that is genuinely concurrent? Are you really optimizing prematurely? Is there really such thing as a "scripting language"? Should operating systems and programming languages keep each other at arm's length? The list goes on.
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