rontolisp:await

(rontolisp:await value)

Given a future, suspends the current asynchronous function until the future settles and returns its settled value. Settled futures never suspend, nested futures flatten, and a value that is not a future passes through unchanged — like a JavaScript await on a non-promise — so await can be applied uniformly to a value that may or may not be a future.

await is a special form, legal only inside rontolisp:async-defun / rontolisp:async-lambda bodies and at top level (the top level is implicitly asynchronous). Anywhere else — a plain defun or lambda body, even one nested inside an asynchronous body — it is an error at compile/definition time:

> (defun bad () (rontolisp:await 1))
rontolisp:await is only allowed inside rontolisp:async-defun/async-lambda or at top level

Errors

A future that settled with an error re-signals that condition at the await — catch it with handler-case around the await: