Scheme is not my first language and I am still greatful for it. I am self learning SICP for past 3 years (after working 15+ years in non-lisp languages). Though still in chapter 2, it has cleared up and simplified my thinking about programming. I no longer consider bottoms up approach to be sin. Understanding new functional language specs becomes a breeze and it 'just clicks'. Though I am yet to understand why Clojure could not implement tail recursion without the 'recur' keyword.
They could for all cases where recur is presently used. Recur serves to indicate and document that the function is supposed to be tail recursive and will cause an error if this is not proper rather than silently not being optimized and blowing up when fed too large an input.
