[vegabook]

machine code looks pretty much like the "essence of computing" to me, and that's about as far as you can get from functional programming. I think I would agree with you more if you meant the essence of computer "science". If I remember correctly there is, anyway, a theorem by Church and Turing that proves imperative and functional programming to be capability-equivalent. The argument is more about the superiority of functional programming in its benefits to software engineering and algorithm discovery by forcing rigour onto our mistake-prone brains.