From @edwinst

The List.squish method variant with the :&as parameter needlessly turns the return value of &as into a Str​:

This is perl6 version 2015.03 built on MoarVM version 2015.03

('', Any, Any).squish(​:as(-> $x {$x})).perl.say
use of uninitialized value $x of type Any in string context in block <unit> at <unknown file>​:1

use of uninitialized value $x of type Any in string context in block <unit> at <unknown file>​:1

("",).list

While this works for unique​:

('', Any, Any).unique(​:as(-> $x {$x})).perl.say
("", Any).list

From @usev6

This was fixed with commit 24931c4307. The tests in S32-list/squish.t are passing now.

I'm closing this ticket as 'resolved'.

@usev6 - Status changed from 'new' to 'resolved'