rontolisp:async-defun

(rontolisp:async-defun name (params...) body...)

Defines an asynchronous function. The surface is the same as defun — the full lambda-list keywords (&optional, &rest, &key, ...) are supported — but calling the function starts the body immediately and returns a future instead of a value: the body runs until its first rontolisp:await of an unsettled future (or until completion), then the caller resumes ("eager start"). The future settles with the value of the last body form, or with the error the body signaled (re-signaled when the future is awaited).

The call itself yields an opaque future (rontolisp:futurep recognizes it, and it prints as #<FUTURE>):

An error signaled by the body does not escape at call time; it settles the future and re-signals at the await — see rontolisp:await for catching it with handler-case. The anonymous counterpart is rontolisp:async-lambda. (rontolisp:async (defun name ...)) — the rontolisp:async wrapper — is an equivalent JavaScript-style spelling.

Backend support

• Interpreter / JVM: the body runs on a virtual thread — real parallelism with the caller after the first suspension.
• WASM --component: the body compiles into a state machine; an await of a pending future genuinely suspends it, and the component's event loop resumes it when the awaited host operation (e.g. a fetch response) completes. The tasks of one component instance are cooperative (single-threaded). An asynchronous component needs wasmtime -W exceptions=y on top of -W gc=y.
• Preview 1 WASM: the body runs to completion immediately (no asynchronous host I/O exists there).
• --no-gc: rejected at compile time.