Bidirectional Coroutines

The bidirectional coroutine is introduced as a mechanism for overcoming a shortcoming in the method of specification of the transfer of control between coroutines. An analogy is drawn between subroutines and coroutines by observing that coroutines, like subroutines, should not have to know with whom they are interacting. At present, most coroutine implementations require specific mention of the coroutine being resumed, or use a s u s p e n d mechanism in which case one coroutine acts as a slave (the suspending one) and the other as a master. In the second case, the slave need not know the identity of its master while the master must know the identity of its slave. For bidirectional coroutines, a coroutine need not know the identity of its master nor its slave. This is achieved by replacing the s u s p e n d primitive with two new primitives r e sume_mas te r and resume_ slave.