In those thing that seem the most simple, may lay the greatest complexity..
This is a search for enlightment. I can see that it works, but I don't know why; is the definition of "faith"?

Page 36 of "Higher Order Perl" contains a function called "find_share", as part of a solution to the partitioning problem. 

sub find_share {
  my ($target, $treasures) = @_;
  return [] if $target == 0;
#  return 0 if $target == 0;    #my code experiment
#  return '' if $target == 0;   #my code experiment
#  return '0' if $target == 0;  #my code experiment
#  return () if $target == 0;   #my code experiment
#  return undef if $target == 0;#my code experiment
  return    if $target < 0 || @$treasures == 0;

  my ($first, @rest) = @$treasures;
  my $solution = find_share($target-$first, \@rest);
  return [$first, @$solution] if $solution;
  return         find_share($target       , \@rest);
}

sub partition {
  my $total = 0;
  my $share_2;
  for my $treasure (@_) {
    $total += $treasure;
  }
  my $share_1 = find_share($total/2, [@_]);
  return unless defined $share_1;
  my %in_share_1;
  for my $treasure (@$share_1) {
    ++$in_share_1{$treasure};
  }
  for my $treasure (@_) {
    if ($in_share_1{$treasure}) {
      --$in_share_1{$treasure};
    } else {
      push @$share_2, $treasure;
    }
  }

## My code to run samples
my ($rslt1,$rslt2) = partition ( 1,5,3,1,6,2 );
if ($rslt1){
  printf "rslt1= %s\n",join ',',@$rslt1;
  printf "rslt2= %s\n",join ',',@$rslt2;
}

[download]
The accompanying text says:
We take care of some trivial cases first. If the target amount is exactly zero, then it's easy to produce a list of treasures that total the target amount: the empty list is sure to have value zero, so we return that right away.
? return the 'empty list' right away? Wouldn't that be ()?
? [] = empty list?

The closer I look, the more puzzling things are. But I think they all revolve around the use of the Anonymous Array Composer to passing references rather than data.

The calling sequence is: 

my $share_1 = find_share($total/2, [@_]);

[download]
which passes as argument 2, I am hoping; the parameter array and re-encapsulates it in an anonymous array and passes the reference to the encapsulation to find_share.
find_share returns references to anon arrays as well. Looking at the variable $solution, I see it is set with the return value from a recursive call the this code; and subsequently used in a Boolean context on the next line.
Checking "perlsyn::Truth and Falsehood" to see what would make $solution FALSE, gives:
The number 0, the strings '0' and '', the empty list "()", and "undef" are all false in a boolean context. All other values are true.
None of those values worked in place of [] (the commented lines). So what type and value is $solution???
It is always better to have seen your target for yourself, rather than depend upon someone else's description.

In reply to A new FALSEness by Wiggins

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