Tail recursion to while iteration in 2 easy steps

[Steven D'Aprano]

On Mon, 07 Oct 2013 15:47:26 -0700, Mark Janssen wrote:

> I challenge you to get
> down to the machine code in scheme and formally describe how it's doing
> both.

For which machine?

Or are you assuming that there's only one machine code that runs on all 
computing devices?


Frankly, asking somebody to *formally* describe a machine code 
implementation strikes me as confused. Normally formal descriptions are 
given in terms of abstract operations, often high level operations, 
sometimes *very* high level, and rarely in terms of low-level "flip this 
bit, copy this byte" machine code operations. I'm not sure how one would 
be expected to generate a formal description of a machine code 
implementation.

But even putting that aside, even if somebody wrote such a description, 
it would be reductionism gone mad. What possible light on the problem 
would be shined by a long, long list of machine code operations, even if 
written using assembly mnemonics?

Far more useful would be a high-level description of Scheme's programming 
model. If names can be rebound on the fly, how does Scheme even tell 
whether something is a recursive call or not?

def foo(arg):
    do stuff here
    foo(arg-1)  # how does Scheme know that this is the same foo?



-- 
Steven