Re: Multiple values passed as single argument to procedure

[Neil Jerram <neil@ossau.homelinux.net>]

On 12/06/17 09:19, Chris Marusich wrote:
> I think I'm missing something here. In (list (f)), the call to f
> certainly looks like it's happening at a position that one might
> intuitively call a "tail" position.  So, in this case, what disqualifies
> f from being in tail position?  Can you give me an example of a call to
> f that would be in tail position, so I can understand the difference?
> Sorry if you've already provided such an example; I appreciate your
> explanations, and I'm just trying to make sure I fully understand.

Mark will probably have a more precise answer for you, but let me offer 
my understanding too.  In general, in

    ( ... arbitrary code around ...
         (f)
      ... )

the (f) call is in a tail position if _nothing_ else needs to be done, 
to the return value(s) of (f), before returning from that block as a whole.

So, common examples of tail position are

   (begin
      ...
      (f))

and

    (if <condition>
        (f))

The case you mentioned, (list (f)), is probably the simplest example of 
a non-tail position, because something very clearly does need to be done 
to the return value of (f): it needs to be inserted into a newly 
allocated list.

Regards - Neil