Tree_from_nesting_levels

#!/usr/local/bin/perl
#u# http://rosettacode.org/wiki/Tree_from_nesting_levels
#c# 2021-02-03 <RC
#p# OK

use strict;
use warnings;
use Data::Dump qw(dd pp);

my @tests =
  (
  []
  ,[1, 2, 4]
  ,[3, 1, 3, 1]
  ,[1, 2, 3, 1]
  ,[3, 2, 1, 3]
  ,[3, 3, 3, 1, 1, 3, 3, 3]
  );

#for my $before ( @tests ) {
#  dd { before => $before };
#  local $_ = (pp $before) =~ s/\d+/ '['x($&-1) . $& . ']'x($&-1) /ger;
#  1 while s/\](,\s*)\[/$1/;
#  my $after = eval;
#  dd { after => $after };
#}

sub nest {
  my $before = shift;
  local $_ = (pp $before) =~ s/\d+/ '['x($&-1) . $& . ']'x($&-1) /ger;
  1 while s/\](,\s*)\[/$1/;
  my $after = eval;
  $after;
}

my $ref = <<'EOD';
{ before => [] }
{ after => [] }
{ before => [1, 2, 4] }
{ after => [1, [2, [[4]]]] }
{ before => [3, 1, 3, 1] }
{ after => [[[3]], 1, [[3]], 1] }
{ before => [1, 2, 3, 1] }
{ after => [1, [2, [3]], 1] }
{ before => [3, 2, 1, 3] }
{ after => [[[3], 2], 1, [[3]]] }
{ before => [3, 3, 3, 1, 1, 3, 3, 3] }
{ after => [[[3, 3, 3]], 1, 1, [[3, 3, 3]]] }
EOD

use Test::More;
is_deeply nest([]), [];
is_deeply nest([1, 2, 4]), [1, [2, [[4]]]];
is_deeply nest([3, 1, 3, 1]), [[[3]], 1, [[3]], 1];
is_deeply nest([1, 2, 3, 1]), [1, [2, [3]], 1];
is_deeply nest([3, 2, 1, 3]), [[[3], 2], 1, [[3]]];
is_deeply nest([3, 3, 3, 1, 1, 3, 3, 3]), [[[3, 3, 3]], 1, 1, [[3, 3, 3]]];
done_testing;