ITA software uses Lisp, and Orbitz gets its flight data from ITA. (Common) Lisp is not, however an especially functional language. Functional programming is po

ITA software uses Lisp, and Orbitz gets its flight data from ITA. (Common) Lisp is not, however an especially functional language. Functional programming is possible, but not the default and not especially structurally encouraged by the language. Most implementations require compiler declarations to get tail-call elimination, and imperative looping is much more common than recursion in production CL code I've seen.