gnd

The await operation blocks until a background task created with async finishes. If the task ends normally, await returns the routine’s output. If the task ends by executing throw, the await itself raises that error message. Thus await either yields a value or propagates the task’s error.

The syntax of await is:

[ $destination ] await [ task ]

• $destination is optional; if omitted, the result is assigned to the special slot _.
• task is optional.
  • If supplied, it must be a task object returned by async.
  • If omitted, await is shorthand for await _, meaning the task object is taken from the current value of _.

Examples

Wait for an explicit task variable:

$task  async heavyWork
$out   await $task            # on success _ becomes the routine's result

Using the default _ shorthand:

$task async buildReport
await                       # same as await $task
log report done

Sequentially await two tasks:

$t1 async stepA
$t2 async stepB
await $t1
await $t2

Error behaviour

• If the resolved operand is not a task object, await raises an error.
• If the task ends with throw, await re-throws the same error.
• Otherwise await returns the task’s normal result.

await never mutates its operand; it blocks the current routine, produces exactly one value on success, and follows single-assignment rules.