my %hash = map {
                  my $foo;
                  $_ => {
                          key1 => $foo = 'longstring'.$_.'more',
                          key2 => alter( $foo ),
                        }
               } @list;

##</code><code>##

my %hash = map {
                  my $foo = { key1 => 'longstring'.$_.'more' };
                  $foo->{"key2"} = alter( $foo->{"key1"} );
                  $_ => $foo;  
               } @list;