On Sun, Dec 13, 2020 at 04:01:24PM +0100, Zelphir Kaltstahl wrote:
> Hi Tomas!
> 
> In some way what you write makes sense. Let me state here, that I did
> read that book and worked through it for a year though, even through the
> complicated parts like the y-combinator and some chapters I must have
> read like 4 or 5 times and discovered new aspects on each try.

That's it -- I'm through some n-th iteration and still go "oh!" from
time to time :-D

> What is typically the case in the book is a different situation though,
> than what was in Taylan's procedure. Usually it is the list you are
> working on in that iteration, which you check for being (null? ...), not
> the thing, that you give as argument to a recursive call or as a return
> value, which you add in some way to the result. Usually the questions
> from the quote are asked once the argument is received in the next
> iteration. That I definitely usually do, but in Taylan's answer there is
> an (if (null? ...) ...) for the `rest`, inside the case, where the usual
> (null? ...) check is already done on the subtree, which we recur on.

I have the hunch that this is only shifting things one level
up or down the stack, but basically, it's the same principle
at work. I'd have to fiddle for a while with that to see whether
I'm totally off, though.

Anyway, a reminder for me to do the n+1st iteration: "Do It, Do
It Again, and Again, and Again, ..." :-)

Thanks for that!

Cheers
 - t