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All,
In this node, tall_man asked how to generate the Hamming Sequence lazily in Perl5. I didn't understand the Haskell code and misunderstood the english explanation.

"how do you generate the series of numbers composed of a given list of prime factors, where each can be used an unlimited number of times?"

I interpreted that to mean all multiples of all prime factors provided minus duplicates were valid. My mistake was exacerbated by the fact the sample series provided fit my interpretation. I took my licks after posting an incorrect solution.

I was happy to take the downvotes and be wrong since the mistake was just as interesting to me. My challenge then is to produce R as shown below for any set of given factors lazily:

Given: Factors 2, 3, 5 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, ... 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, ... 5, 10, 15, 20, 25, 30, ... R = 2, 3, 4, 5, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 2 +6, 27, 28, 30, ...
You can see my cleaned up solution below:
#!/usr/bin/perl use strict; use warnings; use constant HEAD => 0; use constant TAIL => -1; my $end = shift || 10; my @num = @ARGV ? @ARGV : (2, 3, 5); my $next = merge_multiple( \@num ); print $next->(), "\n" for 1 .. $end; sub merge_multiple { my $list = shift; return () if ! $list || ref $list ne 'ARRAY'; my $n = 1; my $h = $list->[TAIL]; my (@pool, @stream); return sub { return shift @pool if @pool; for ( 0 .. $#$list ) { my $mult = $list->[ $_ ]; my $beg = $h * ($n - 1) / $mult + 1; my $end = $h * $n / $mult; $stream[ $_ ] = [ map { $mult * $_ } $beg .. $end ]; } ++$n; @pool = merge( \@stream ); return shift @pool; } } sub merge { my $stream = shift; my $end = $#$stream; my @merged; while ( 1 ) { my $low; for ( 0 .. $end ) { my $val = $stream->[ $_ ][HEAD]; next if ! defined $val; $low = $_ if ! defined $low || $val < $stream->[ $low ][HE +AD]; } last if ! defined $low; my $num = shift @{ $stream->[ $low ] }; next if defined $merged[ TAIL ] && $merged[ TAIL ] == $num; push @merged, $num; } return @merged; }

Cheers - L~R


In reply to Challenge: Another Infinite Lazy List by Limbic~Region

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