Forking GitHub issue

{"vibecode": {
    "doc": "forking",
    "role": "spec for Caspian's forking — how user code spawns OS-level child processes; the fork-point call returns to both processes, with the return value discriminating parent (manager object) from child (null)",
    "status": "in progress — replacing the prior design (see old.md); examples added incrementally",
    "key_concepts": ["fork_point_call_returns_to_both_processes",
        "return_value_discriminates_parent_from_child",
        "parent_gets_manager_object",
        "child_gets_null",
        "if_child_is_the_parent_only_idiom"]
}}

Forking in Caspian follows the classic Unix fork() shape: a single call that returns in both the parent and the freshly-spawned child. The return value tells each side which one it is — the parent gets a fork manager object, the child gets null. Code that follows the fork point runs in both processes.

Simplest fork GitHub issue

$child = %utils.forks.branch

$child   # fork manager object in parent process
$child   # null in child

if $child
    $child.wait()
    $child.status   # only available after wait()
    $child.stdout   # only available after wait()
    $child.stderr   # only available after wait()
end

%utils.forks.branch is the fork point. After it returns, the script is running in two processes:

• Parent. $child holds the fork manager object. The parent can wait for the child to finish, inspect its exit status, read its captured output, etc.
• Child. $child is null. The child continues executing the script from this line forward, just without a manager.

The if $child block runs only in the parent. The child, with $child as null (a falsy value), skips it.

Methods on the fork manager: