gistfile1.txt

use v6;
#use Slang::Tuxic;

my %cb;

class B {
    has Int $.i is rw = 0;
    }

class C {

    has B @!f = (B.new(i => 1), B.new(i => 2));

    method foo {
        defined %cb{"cb"} and %cb{"cb"}.(self, @!f);
        return @!f;
        }
    }

C.new.foo().perl.say;
%cb{"cb"} = sub (C $c, B @f) { }; # NO ACTION AT ALL
C.new.foo().perl.say;


==>

when Slang::Tuxic active, I get

===SORRY!=== Error while compiling t.pl
Unable to parse expression in argument list; couldn't find final ')'
at t.pl:21
------> %cb{"cb"} = sub (C⏏ $c, B @f) { }; # NO ACTION AT ALL
    expecting any of:
        infix stopper
        infix or meta-infix
Exit 1