my $out .= "var ";

my $out .= "var ";

##</code><code>##

(Shapes => 
  [ 
    { Type => 'Circle', Diameter => 2, Center => [0,1] }, 
    { Type => 'Square', Side => 3, Pos => [4,8] },
    [ {x => 1, y => 1}, {x => 3, y => 1}, {x => 4, y => 2}, {x => 2, y => 2} ]
  ]
);

##</code><code>##

var is a HASH with 5 keys
        the keys are 'age', 'fname', 'kids', 'last_name', 'occupation'
        key 'kids' is an ARRAY containing HASHREFs:
                the keys are 'age', 'name', 'vaccinated'
                key 'vaccinated' is a SCALAR
                key 'age' is a SCALAR
                key 'name' is a SCALAR
        key 'fname' is a SCALAR
        key 'age' is a SCALAR
        key 'occupation' is a HASH with 2 keys
                the keys are 'title', 'years_on_job'
                key 'title' is a SCALAR
                key 'years_on_job' is a SCALAR
        key 'last_name' is a SCALAR

##</code><code>##

use v5.14;

use strict;
use warnings;

use Data::Dump qw( pp );
use YAML;

sub introspect
{
  my ($data, $output) = @_;
  if (ref $data eq 'ARRAY')
  {
    my $sub_out = ($output->{'ARRAY'} //= {});
    introspect($_, $sub_out) for @{ $data };
  }
  elsif (ref $data eq 'HASH')
  {
    my $hash_out = $output->{"HASH"} //= {};
    for my $key (keys %$data)
    {
      my $sub_out = ($hash_out->{"$key"} //= {});
      introspect($_, $sub_out) for $data->{$key};
    }
  }
  elsif (ref $data)
  {
    $output->{ref($data).'REF'}=1;
  }
  else
  {
    $output->{SCALAR}=1;
  }
}

my @array = ({fname => 'bob',  last_name => 'smith', foo => [\*main]},

             {fname => 'tony', last_name => 'jones', age => 23,
               kids =>
                 [
                   {first_name   => 'cheryl',
                    middle_name => 'karen',
                    age         => 24        },

                   {name         => 'jimmy',
                    age          => 17       }

                 ],
                                                },
             {fname => 'janet', last_name => 'marcos', foo => {},
               occupation => {
                 title => 'trucker',
                 years_on_job => 12}                              },


             {fname => 'Marge', last_name => 'Keefe',
                kids =>
                  [
                    {name => 'kate', age => 7, vaccinated => 'yes'},
                    {name => 'kim', age => 5}
                  ]
             });
             
my %out;

introspect(\@array, \%out);
say pp \%out;
say YAML::Dump(\%out);

##</code><code>##

{
  ARRAY => {
    HASH => {
      age => { SCALAR => 1 },
      fname => { SCALAR => 1 },
      foo => { ARRAY => { GLOBREF => 1 }, HASH => {} },
      kids => {
        ARRAY => {
          HASH => {
            age => { SCALAR => 1 },
            first_name => { SCALAR => 1 },
            middle_name => { SCALAR => 1 },
            name => { SCALAR => 1 },
            vaccinated => { SCALAR => 1 },
          },
        },
      },
      last_name => { SCALAR => 1 },
      occupation => {
        HASH => { title => { SCALAR => 1 }, years_on_job => { SCALAR => 1 } },
      },
    },
  },
}
---
ARRAY:
  HASH:
    age:
      SCALAR: 1
    fname:
      SCALAR: 1
    foo:
      ARRAY:
        GLOBREF: 1
      HASH: {}
    kids:
      ARRAY:
        HASH:
          age:
            SCALAR: 1
          first_name:
            SCALAR: 1
          middle_name:
            SCALAR: 1
          name:
            SCALAR: 1
          vaccinated:
            SCALAR: 1
    last_name:
      SCALAR: 1
    occupation:
      HASH:
        title:
          SCALAR: 1
        years_on_job:
          SCALAR: 1


##</code><code>##

  elsif (ref $data eq 'REF')
  {
    introspect($$data, ($output->{'REF'} //= {}));
  }