Somewhat similar to the pure-Perl implementation in List::Util itself...

use vars qw($a $b);

sub reduce (&@) {
  my $code = shift;
  
  return shift unless @_ > 1;
  
  my $caller = caller;
  local(*{$caller."::a"}) = \my $a;
  local(*{$caller."::b"}) = \my $b;
  
  $a = shift;
  foreach (@_) {
    $b = $_;
    $a = &{$code}();
  }

  $a;
}
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Although if the XS compiles and loads, this code is not used.

-- Randal L. Schwartz, Perl hacker