From @japhb

It appears you can't use an rx{} literal as a parameter default​:

$ perl6 -e 'sub foo($r) { say $r }; foo(rx{bar});'
rx{bar}
$ perl6 -e 'sub foo($r = rx{foo}) { say $r }; foo(rx{bar});'
===SORRY!===
Cannot call method 'match' on a null object
$ perl6 -v
This is perl6 version 2015.06-314-g5d1ec3c built on MoarVM version
2015.06-98-gf22142b

This is golfed down from a bug causing flussence's Text-Tabs-Wrap
module Text​::Wrap to no longer compile, throwing the above SORRY!
error right when it tries to parse the params to sub wrap().

Interestingly there appears to be a funky workaround​:

$ perl6 -e 'sub foo($r = {rx{foo}}()) { say $r }; foo(rx{bar}); foo();'
rx{bar}
rx{foo}

From @jnthn

On Thu Jul 23 19​:11​:18 2015, gjb@​google.com wrote​:

It appears you can't use an rx{} literal as a parameter default​:

$ perl6 -e 'sub foo($r) { say $r }; foo(rx{bar});'
rx{bar}
$ perl6 -e 'sub foo($r = rx{foo}) { say $r }; foo(rx{bar});'
===SORRY!===
Cannot call method 'match' on a null object
$ perl6 -v
This is perl6 version 2015.06-314-g5d1ec3c built on MoarVM version
2015.06-98-gf22142b

This is golfed down from a bug causing flussence's Text-Tabs-Wrap
module Text​::Wrap to no longer compile, throwing the above SORRY!
error right when it tries to parse the params to sub wrap().

Interestingly there appears to be a funky workaround​:

$ perl6 -e 'sub foo($r = {rx{foo}}()) { say $r }; foo(rx{bar}); foo();'
rx{bar}
rx{foo}

Turned out to be a funky "static analysis gone wild" bug. Fixed, added test in S06-signature/defaults.t.

The RT System itself - Status changed from 'new' to 'open'

@jnthn - Status changed from 'open' to 'resolved'