gistfile1.txt

sub with-optional($arg?) { # <--- $arg defaults to `Any` type object, if no argument is given
  say "bob";  # <--- output string `bob`; return True; discard return value
  $arg; # <--- return value used for `with-optional` sub
}

with-optional; # no arg given, so `with-optional`'s argument default to `Any`. It's used as return value, which is discarded here
with-optional(1); # arg is 1; it's used as return value, so return value is `1`, which is discarded here
say with-optional; # no arg = `Any` return value from `with-optional`, which is given as argument to `say, 
                   # which outputs it as a string (after some processing). The `say` returns True, which is then discarded
say with-optional(1); # 1 as arg = 1 as return value from `with-optional`, which is given as argument to `say, 
                   # which outputs it as a string (after some processing). The `say` returns True, which is then discarded