Process handle (int)

spawnProcess returns Result<int, Error>: the success value is the process ID used by awaitProcess and cleanupProcess. There is no separate built-in ProcessHandle type. The required callback receives (processID, eventType, data); event types are stdout (1), stderr (2) and exit (3).

Example

fn onEvent(_pid, kind, data) = print("${kind}: ${trim(data)}")
match spawnProcess("echo hello", onEvent) {
    Success { value } => {
        let exitCode = awaitProcess(value)
        cleanupProcess(value)
        print("exit: ${exitCode}")
    }
    Error { message } => print("Process failed: ${message}")
}

onEvent (_pid, kind, data) = print "${kind}: ${trim data}"
match spawnProcess "echo hello" onEvent
    Success value =>
        exitCode = awaitProcess value
        cleanupProcess value
        print "exit: ${exitCode}"
    Error message => print "Process failed: ${message}"

The callback prints output and exit events; the final line reports the status returned by awaitProcess. Call cleanupProcess after waiting. The ML callback uses a flat three-argument signature to match the runtime slot.

Process spawning is a native capability; --sandbox rejects it. WebAssembly, mobile archive and Python-host targets do not provide it.