$ perl6 -e'my Int $n = 10; say ++$n;'
11
$ perl6 -e'my int $n = 10; say ++$n;'
Cannot assign to an immutable value
  in sub prefix:<++> at src/gen/m-CORE.setting:5565
  in block <unit> at -e:1
$ perl6 -e'my int $n = 10; say [+] ^$n'
45
$ perl6 -e'my int $n = 10; say [+] ^$n,$n'
55