output.log

-> ;; $_? is raw = OUTER::<$_> { #`(Block|69979400) ... }
this is baz
-> ;; $_? is raw = OUTER::<$_> { #`(Block|69986960) ... }
this is bar
-> ;; $_? is raw = OUTER::<$_> { #`(Block|69987104) ... }
this is foz
(Callable)
No such method 'CALL-ME' for invocant of type 'Callable'
  in method run at attint.raku line 19
  in block <unit> at attint.raku line 22

testfile.raku

#!/usr/bin/env raku
use v6;
class Foo {
   has &!foo = { put 'this is foo' };
   has &!bar;
   has &!baz;
   has &!foz = { put 'this is foz' };
   method BUILD (:&!foo, :&!bar = { put 'this is bar' }, :&!baz) {
      &!baz //= { put 'this is baz' }
   }
   method run {
      &!baz.say;
      &!baz();
      &!bar.say;
      &!bar();
      &!foz.say;
      &!foz();
      &!foo.say;
      &!foo();
   }
}
Foo.new.run;