use strict ;
use warnings ;
use Data::Dumper ;

my $h1 = { a => 1, b => 2 } ;
my $h2 = { a => 1, c => 3 } ;

foreach( keys %{ $h2 } ) {
	merge( $h1 )->( $_ ) += $h2->{ $_ } ;
}

print Dumper( $h1 ) ;

sub merge : lvalue {
	my $inh = $_[0] ;
	my $ret = sub : lvalue {
		$inh->{ $_[0] } ;
	} ;
	$ret ;
}