$s1 = hello
$s2 = \sworld

fn.println($s1 world)
# Output: hello world

fn.println($s1$s2)
# Output: hello world

fn.println(fn.concat($s1, $s2))
# Output: hello world

fn.println(parser.op($s1 ||| $s2))
# Output: hello world

fn.println(fn.add($s1, $s2))
# Output: hello world

fn.println(parser.op($s1 + $s2))
# Output: hello world