... I remember meeting Rich Hickey at conference when he'd seen a tweet where I'd favorably compared Clojure to Scala. I had a hard time explaining to him, however, how a professor who wrote FORTRAN programs to simulate the behavior of materials (other academics would be quite shocked when he'd explain that we actually could figure out that iron is magnetic from first principles... I regret missing out on his class on density functional theory as much as I regret not taking a compilers class) told me that a 2x difference in performance mattered so much when you were running big jobs in computers. Thus you weren't going to get everybody impressed with the power of immutability. I am writing a chess engine in Java right now and completely in tune with, in the long term, not making any objects at all in the inner loop or the next loop out.

But yeah, CL was one of the first languages specified by adults and set the standard for other specs like Java that read cleanly and don't have the strange circularity that you notice in K&R. So many people have this abstract view that a specification should be written without implementation in mind, but really the people behind CL weren't going to be implementable and clearly they'd given up on the "Lisp machine" idea and made something that the mainstream 32 bit machine could handle efficiently. It's quite beautiful and had a larger impact on the industry than most people admit.

(I think how C is transitional between failures like PL/I and modern languages like CL and Java that can be specced out in a way that works consistently)