$lamb=sub { my($x,$y)=\(@_); $$x += $$y }

You just have to restrict referencing to arguments which are read/write and copying to read-only args.

Such that $$x signals clearly "x is an alias" and $y "y is only a copy".

 $lamb=sub { my $x= \shift; my ($y)=@_; $$x += $y }

Your code becomes much clearer and unintended changes to the original of $y are impossible, avoiding ugly and very hard to track bugs!!!

Unfortunately its not possible to write this as dense (but more error-redundant) than in ruby...

 
$lamb=sub { my ($$x,$y)=@_; $$x += $y } 
#  Can't declare scalar dereference in "my"
[download]

But maybe I'm missing another "way to do it"? ( would be please to know 8)

UPDATE: Of course you can use arraslices

 $a=sub { my($x,$y)=(\(@_[0]),@_[1]); $$x +=$y }

or

 $a=sub { my($x,$y)=(\($_[0]),$_[1]); $$x +=$y }

link to footnotes within my own comment, so I'll just leave others to navigate manually.

sure you can define anchor-names with a-tags and link to them with href to #name. E.g these KISSes are interlinked. Just look in the HTML-Source...

But I doubt footnotes may help clarify your update-inferno... ;-)