$VAR1 = bless( { 
    		'c_xcode' => 'J23-H0P',  
    		'c_ycode' => 'G12-Y4T', 
    		'c_zcode' => 'Q87-S7B',
    		's_xlist' => 'T66-Y9A',
    		's_ylist' => 'A43-P9W',
    		's_zlist' => 'T71-K2L'
     		}, 'Hash::MultiValue' ); 
		

##</code><code>##

    %form_hash = (
    				'c_xcode' => 'J23-H0P',  
    				'c_ycode' => 'G12-Y4T', 
    				'c_zcode' => 'Q87-S7B',
    				's_xlist' => 'T66-Y9A',
    				's_ylist' => 'A43-P9W',
    				's_zlist' => 'T71-K2L'
    			);


##</code><code>##

my $form =  $posted->body_parameters;
my @k = keys %$form;
my @v = values %$form;
@form_hash{@k} = @v;

# Dumper ( \%form_hash) works, but can't pass this to foreach;
# "Experimental keys on scalar is now forbidden" when trying on 
# foreach my $key (sort(keys(  \%form_hash   ))) below.


##</code><code>##


    #!/usr/bin/perl
    
    use strict 'refs';
    use Plack::Request;
    use Data::Dumper;
    
    my $app = sub {
    
    	my $env = shift;
    	my $form = Plack::Request->new($env);
    	
    	print Dumper ( $form->body_parameters ) ;
    	
    	#how to convert $form->body_parameters to new  %form_hash?
    	
    	my %form_hash;
    	my %cb_hash;
    	
    	foreach my $key (sort(keys(  %form_hash   ))) {
    
    	 if ( substr($key,0,2) eq "c_" ){    
    				
    		my $cb_key = $key;
            	my $cb_val = $form_hash{$key};
            	$cb_hash{$cb_key} = $cb_val; 
    
    			}
    
    	}
    
    };