The Portable Coroutine Library (PCL) implements the low level functionality
for coroutines. For a definition of the term coroutine see The Art of Computer
Programming by Donald E. Knuth. Coroutines are a very simple cooperative
multitasking environment where the switch from one task to another is done
explicitly by a function call. Coroutines are a lot faster than processes or
threads switch, since there is no OS kernel involvement for the operation. Also
coroutines require much less OS resources than processes of threads.