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Comment by smanek | Hacker News Reader

IIRC, ITA Software (one of the biggest Lisp houses in the world ...) uses SBCL for their main QPX project. A few years ago when they were starting the new Polaris project, they decided to go with CCL instead of continuing with SBCL.

My understanding is that the two major motivating factors for this decision were that CCL compiles faster and has better debugging support.

This is all based on my memory of conversations that took place about a year ago, so it's entirely possible I'm mis-remembering or what used to be true no longer holds. I have no first hand experience with CCL so if you do, I'll take your word for it ...

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I currently work on QPX, the air travel search engine. We continue to use SBCL, primarily because it produces faster code for our workload. We and our customers are very sensitive to the performance of the application.

Dan Weinreb, another ITA developer, did a talk at Google a few months ago on ITA's new reservation system (the Polaris project you mention). They do use CCL, but the code also compiles and runs with SBCL. The primary reason he cites in that talk for preferring CCL over SBCL (about 22 minutes in) is that CCL compiles code more quickly than SBCL.

I haven't used CCL much, but I understand SBCL and CCL have different debugging strengths. An SBCL developer tells me that a significant chunk of the compilation time for our application is in constraint propagation for types. That's part of the "generates more efficient code", but it also means that it's smart about telling you when you're doing something that's not going to work. For whatever reason, type propagation or otherwise, CCL won't do as much to help you at compile time. I am told that CCL gives better stack traces, so SLIME can help you more.

Yeah, that vibes with I've seen in SBCL (and been told about CCL). Thanks for the inside scoop.

Remember also that during the time that ITA would have made that decision, SBCL and SLIME were both evolving rapidly.

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