During those entire 50 years, people have been saying “Lisp is impractical”; “Lisp is too slow”; “procedure calling is too expensive”; “only professors care about Lisp.” They’re still saying it. But meanwhile, users — real users — who would never dare give their bosses a program written in Lisp are demanding Lisp’s ideas in the programming languages they do use. Today you take recursion for granted, but it was a radical idea when Lisp introduced it. (Fortran didn’t have recursive procedures until fairly late in its history; the early personal computer users made do with BASIC, which, in those early versions, had no procedure calling at all.) Users of strongly typed languages demanded, and got, Lisp’s heterogeneous lists. Today, the radical Lisp idea that’s invading the mainstream is first class procedures. Guido van Rossum, the inventor of Python, hates Lisp, but he was dragged kicking and screaming by users into providing [a half-assed version of] lambda in Python. Even C++, a notorious can of worms, has added lambda in its most recent version. Lambda in Java is coming in 2013. In another decade they’ll probably discover first class continuations.