Re: [FWP] Re: Neat or horrid?

[Ariel Scolnicov <ariels@compugen.co.il>]

kragen@pobox.com (Kragen Sitaker) writes:

> Ariel Scolnicov wrote:
> > Neat, but not as neat as primality testing...
> > 
> > Does it do proper tail recursion?  If not, I'd try
> > 
> >      sub sum {@_ ? shift () + goto &sum : 0}
> > 
> > except that it doesn't work (5.005_03).  I don't think I understand
> > why not, though.
> 
> It's not tail-recursive --- the continuation for the call to &sum is
> (in Scheme) (lambda (val) (+ (shift) val)), not (lambda (val) val),
> which is what it would need to be for proper tail-recursion.
> 
> You could do something like
> 
> #!/usr/bin/perl -w
> use strict;
> sub sum { if ($#_) { unshift @_, shift() + shift; goto &sum } else { $_[0] }}
> print sum (37), "\n";
> print sum (48, 31, 11), "\n";
> 
> That's properly tail-recursive, but I don't think it's properly Fun.

Thanks for the many people who posted, setting me straight.  Thanks
especially to Kragen, who took the trouble to post the Right Thing.

-- 
Ariel Scolnicov        |"GCAAGAATTGAACTGTAG"            | ariels@compugen.co.il
Compugen Ltd.          |Tel: +972-2-6795059 (Jerusalem)	\ We recycle all our Hz
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