undefinedp - determine whether or not a given value is undefined. int undefinedp( mixed arg ); Return 1 if `arg' is undefined. 'arg' will be undefined in the following cases:
* it is a variable set equal to the return value of a call_other to a non-existent method (e.g. arg = call_other(obj, "???")). * it is a variable set equal to the return value of an access of an element in a mapping that doesn't exist (e.g. arg = map[not_there]). * it has not yet been initialized. * it points to a destructed object. * it is a function (formal) parameter that corresponds to a missing actual argument.
Tim Hollebeek Beek@ZorkMUD, Lima Bean, IdeaExchange, and elsewhere