# In languages with ‘general’ or ‘full’ coroutines, the ‹yield› (or
# ‹resume›) operation takes the form:
#
#     result = yield <value> to <coroutine>
#
# This cannot be directly written in Python, yet earlier we have
# claimed that thanks to first-class nature of coroutines and the
# fact that they can be resumed from anywhere (though they cannot
# themselves yield to arbitrary other coroutines).