push @$list, $$items[$i];
comb_integral($items, $group - 1, $list, $i + 1);
pop @$list;

##</code><code>##

comb_integral($items, $group - 1, [@$list, $$items[$i]], $i + 1);

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;

use Data::Dumper;

my @list = (1 .. 5);
my $take = 2;

my @combs = comb_integral(\@list, $take);
for my $comb (@combs) {
  print "@$comb\n";
}

sub comb_integral {
  my ($items, $group, $next) = @_;
  $next ||= 0;

  if ($group == 1) {
    return map [$_], @$items[$next..$#$items];
  } else {
    my @returns;
    for my $i ($next..$#$items) {
      push @returns, map [$$items[$i], @$_], comb_integral($items, $group - 1, $i + 1);
    }
    return @returns;
  }
}

##</code><code>##

push @returns, my @combs = comb_integral($items, $group - 1, $i + 1);
unshift @$_, $$items[$i] for @combs;

##</code><code>##

Benchmark: running SparkyG, demerphq, integral2, intgrl2_f, intgrl_np, intgrl_pp, iterative, each for at least 1 CPU seconds...
   SparkyG:  1 wallclock secs ( 1.06 usr +  0.01 sys =  1.07 CPU) @ 1570.09/s (n=1680)
  demerphq:  1 wallclock secs ( 1.05 usr +  0.02 sys =  1.07 CPU) @ 2283.18/s (n=2443)
 integral2:  2 wallclock secs ( 1.10 usr +  0.02 sys =  1.12 CPU) @ 3428.57/s (n=3840)
 intgrl2_f:  2 wallclock secs ( 1.07 usr +  0.02 sys =  1.09 CPU) @ 2900.92/s (n=3162)
 intgrl_np:  2 wallclock secs ( 1.08 usr +  0.00 sys =  1.08 CPU) @ 3110.19/s (n=3359)
 intgrl_pp:  1 wallclock secs ( 1.05 usr +  0.00 sys =  1.05 CPU) @ 3199.05/s (n=3359)
 iterative:  1 wallclock secs ( 1.04 usr +  0.01 sys =  1.05 CPU) @ 4265.71/s (n=4479)
            Rate SparkyG demerphq intgrl2_f intgrl_np intgrl_pp integral2 iterative
SparkyG   1570/s      --     -31%      -46%      -50%      -51%      -54%      -63%
demerphq  2283/s     45%       --      -21%      -27%      -29%      -33%      -46%
intgrl2_f 2901/s     85%      27%        --       -7%       -9%      -15%      -32%
intgrl_np 3110/s     98%      36%        7%        --       -3%       -9%      -27%
intgrl_pp 3199/s    104%      40%       10%        3%        --       -7%      -25%
integral2 3429/s    118%      50%       18%       10%        7%        --      -20%
iterative 4266/s    172%      87%       47%       37%       33%       24%        --