This definitely lowers my opinion of BeOS. The coding style used is terrible! You should never name your predicates is_something. A predicate is not asking a question, it is answering it. Consider this code fragment:
if (is_computer_on_fire()) {

You cannot read it out loud, because it doesn't sound like English.

Much better alternatives would be computer_is_on_fire(), computer_on_fire() or the Lisp-like computer_on_fire_p() (using the -P convention). All of these let you read your code.