Given a flat list of integers greater than zero, representing object nesting
levels, e.g. [1, 2, 4],
generate a tree formed from nested lists of those nesting level integers where:

 Every int appears, in order, at its depth of nesting.
 If the next level int is greater than the previous then it appears in a sub-list of the list containing the previous item


The generated tree data structure should ideally be in a languages nested list format that can
be used for further calculations rather than something just calculated for printing.



An input of [1, 2, 4] should produce the equivalent of: [1, [2, [[4]]]]
where 1 is at depth1, 2 is two deep and 4 is nested 4 deep.

[1, 2, 4, 2, 2, 1] should produce [1, [2, [[4]], 2, 2], 1]. 

All the nesting integers are in the same order but at the correct nesting
levels.

Similarly [3, 1, 3, 1] should generate [[[3]], 1, [[3]], 1]

Task

Generate and show here the results for the following inputs:

 []
 [1, 2, 4]
 [3, 1, 3, 1]
 [1, 2, 3, 1]
 [3, 2, 1, 3]
 [3, 3, 3, 1, 1, 3, 3, 3]


#!/usr/bin/perl
 
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 };
  }