SYNOPSIS
    mixed * P_HBHOOKS  "HbHooks"

    mixed * SetHbHooks(mixed * value)
    mixed * QueryHbHooks()

      used via

    void AddHeart (mixed hook)
    void RemoveHeart (mixed hook)
    int CheckHeart (mixed hook)

DESCRIPTION
    The heartbeat hooks are a list of functions to be called in every
    heartbeat of the living. The functions have to return a non-zero
    value if they want to be called again in the next heartbeat, and
    a zero value if no further call is necessary.

    A hook can be a string with the name of the function to call, or
    a closure to execute. In the former case, the function has to be
    implemented by the living itself, in the latter case it can be
    an outside function.

    The list of hooks is maintained through the functions AddHbHook()
    and RemoveHbHook(). Multiple calls to one function for the same
    hook are allowed.

EXAMPLE

    AddHbHook(#'talk_more);     // Call talk_more() in the next heart_beat.
    RemoveHbHook(#'talk_more);  // Stop calling talk_more()

BUGS
    If the same function is added once as string and once as closure,
    it is called twice.
    
AVAILABILITY
    Include: <properties.h>

    Availability: /std/living (/heart)

SEE ALSO
    heart(p)