unCLog

One of Common Lisp's darker arts is optimizing functions. It's a beautiful idea: don't worry (too much) about performance until you've found the critical sections of your code; then tell the compiler what you'd like and, voila, faster code. Since compilers differ, however, and since you're never quite sure what incantation is going to convince Lisp to do "the right thing" (*), you're often left flipping declarations around like hot potatoes.

Enter Allegro Common Lisp, version 8.0 I've been working lately (for money even!) in ACL and one of the wonderful new features is that you can ask the compiler to tell you what it thinks and what it wants. I've wanted this ability for a long time (I even talked about it at ILC 200? in NYC). Let the programming environment notice that such and such a function is suboptimal and tell me that if I scratch it's back (with a little more information), then it can scratch mine (with a little more performance). ACL's explain feature isn't quite that, but it's a great step in that direction.

(*) I.e., what you want it to. Joke.

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