{$spawn {
    {$loop {
        {$stdout writeln a}
    }}
}}

spawn executes a list of statements in a new thread.

{$co {
    {$map i [$range 1 20] {
        {$stdout writeln $i}
    }}
}}

co puts a list of statements in a queue. If the queue is empty, co starts a thread that calls each item in the queue, then exits.

The statements must not block.