Here's my new go to prime-factors function :
sub prime-factors( Int $n is copy where * > 1 ) {
gather {
while ( $n > 1 ) {
if ( $n.is-prime ) {
take $n;
last;
}
my $f = (2..^$n/2).grep($n %% *).first(*.is-prime);
take $f;
$n = $n div $f
}
}
}
On Fri, 17 Jun 2022 at 03:51, Simon Proctor <[email protected]> wrote:
> This is because if there isn't an explicit return the last statement
> evaluated is the implied return value.
>
> So the last call (which returns Nil) was your implicit return.
>
> Generally I try and avoid an implicit return if a function has more than a
> couple of lines.
>
> On Thu, 16 Jun 2022, 21:41 Rick Bychowski, <[email protected]> wrote:
>
>> For example here:
>>
>>
>> https://github.com/manwar/perlweeklychallenge-club/blob/master/challenge-168/rick-bychowski/raku/ch-2.raku
>>
>> I called the recursive function at various points in an if/else
>> statement, but each call was always the very last statement of the
>> branch/routine. Otherwise, even a trailing "last" or "exit" silently
>> "fails".
>>
>> All good!
>>
>> - Rick
>>
>> On 6/16/22 13:21, Rick Bychowski wrote:
>> > Yep, the "return factors($q, @f)" fixes it. I've not called a recursion
>> > from anywhere other than the end of a routine, so haven't run into this
>> > issue before. Learned something today!
>> >
>> > Thanks to Simon, William and Andinus for your assistance!
>> >
>> > - Rick
>> >
>> > On 6/16/22 11:07, Simon Proctor wrote:
>> >> I think, and I don't have my computer to hand to double check but I
>> >> think you want a return before your recursive.call to factors passing
>> >> in @f.
>> >>
>> >> When dealing with recursive functions you need to make sure what
>> >> you're returning back up the stack.
>> >>
>> >>
>> >>
>> >> On Thu, 16 Jun 2022, 18:10 Rick Bychowski, <[email protected]
>> >> <mailto:[email protected]>> wrote:
>> >>
>> >> Hi Everyone,
>> >>
>> >> I've been lurking quite a while, this will be my first post to
>> perl6
>> >> users. I've written a lot of short scripts in perl5 for system
>> admin
>> >> type stuff at home and work. Lately I'm playing with Raku, which
>> is a
>> >> lot of fun. Error reporting is excellent, as is the online
>> >> documentation.
>> >>
>> >> To the point. I recently started the perl weekly challenge. Lots of
>> >> math/primes stuff. I wrote an algorithm to list all the prime
>> >> factors of
>> >> an integer, using a recursive subroutine. I'm able to print the
>> >> result
>> >> from the subroutine, but it always returns Nil. What am I missing?
>> >>
>> >> #!/usr/bin/env raku
>> >>
>> >> sub MAIN($n = 20) {
>> >> .say for factors($n); # Nil
>> >> }
>> >>
>> >> sub factors($n, @factors?) {
>> >> my @f = @factors.elems ?? @factors !! ();
>> >> my $q;
>> >> for 2 ..^ $n -> $i {
>> >> if $n %% $i {
>> >> $q = Int($n / $i);
>> >> @f.push($i);
>> >> if $q.is-prime {
>> >> @f.push($q);
>> >> say @f; # [2 2 5]
>> >> return @f;
>> >> } else {
>> >> factors($q, @f);
>> >> }
>> >> last;
>> >> }
>> >> }
>> >> }
>> >>
>> >> Returns
>> >> [2 2 5]
>> >> Nil
>> >>
>> >> -- Rick Bychowski
>> >>
>> >> The information in this email is confidential and may be legally
>> >> privileged. It is intended solely for the addressee(s). Access to
>> >> this
>> >> e-mail by anyone else is unauthorized.
>> >>
>> >
>>
>> --
>> Rick Bychowski
>>
>> The information in this email is confidential and may be legally
>> privileged. It is intended solely for the addressee(s). Access to this
>> e-mail by anyone else is unauthorized.
>>
>
--
Simon Proctor
Cognoscite aliquid novum cotidie
http://www.khanate.co.uk/
