Google Common Lisp Style Guide
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Reference: Google Common Lisp Style Guide
In April 2011, Google acquired ITA Software. ITA provides airline flight search for several of the major companies. The interesting thing is that ITA's search engine was written in Common Lisp.
This style guide shows that Google is adopting the existing Lisp code base instead of rewriting it. Not so surprising since the code is, from what I have heard, well-engineered. But a bit surprising since Google chose Python over Lisp some time ago. Peter Norvig explains the choice a bit on Reddit and Hacker News.
In addition, it also shows that Google is affecting ITA with its culture, to some degree. Google uses this format for all of its style guides.
Anyway, I love style guides!