How do I use chr inside a regex?

[ToddAndMargo via perl6-users]

Hi All,

How do I use chr inside a regex.  In the below, how
do I get rid of $y?
$ p6 'my Str $x=chr(0x66)~chr(0x77); my Str $y=chr(0x66)~chr(0x77); 
$x~~s/ $y /xy/; say $x;'

xy


Many thanks,
-T