And neither is Linux completely implemented in C, and C compilers written in C are not completely implemented in C, because bits and pieces of the libraries they link their code to are written in assembly.

> Yes, the assembly part of it looks difficult to me. When I look at Arc or Lisp code I don't see any way to translate that to native code. Obviously has been done, I'm just not educated on such matters.

The Lambda the Lutimate papers are a good place to start if you're interested - they include some hand-written assembly code equivalents to Scheme/Lisp code, largely function calls and prefix/suffix. Given that the most basic axioms of Arc include (fn ...) and a function call syntax, this would be quite of interest.

> But suppose I can't trust CL to do tail recursion. What am I supposed to do about it?