Based on saintmike's code - here is one way to move the "HoA when necessary" complexity to the CALLED subroutine: 
use Data::Dumper;

use strict;
use warnings;

simple_call(
      animal => 'monkey',
      fish   => 'tuna',
      insect => 'ant',
      insect => 'spider'
);

##########################
sub simple_call {
    my %params;

    while(my($key, $value) = splice @_, 0, 2) {
        if (exists $params{$key}){
           if (ref $params{$key} eq "ARRAY"){
              push @{$params{$key}},$value;
           }else{
              $params{$key} = [$params{$key},$value];
           }
        }else{
            $params{$key} = $value;
        }
    }
    print Dumper \%params;
}

[download]
prints 
$VAR1 = {
          'insect' => [
                        'ant',
                        'spider'
                      ],
          'animal' => 'monkey',
          'fish' => 'tuna'
        };

[download]
Update:Corrected attribution to saintmike, and deleted unnecessary @params declaration.

     "Man cannot live by bread alone...
         He'd better have some goat cheese and wine to go with it!"

In reply to Re: How to process named parameters that have the same key name? by NetWallah
in thread How to process named parameters that have the same key name? by Anonymous Monk

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