zh.wikipedia.org/wiki/協程

與子例程一樣，協程也是一種程序組件。相對子例程而言，協程更為一般和靈活，但在實踐中使用沒有子例程那樣廣泛。協程源自Simula和Modula-2語言，但也有其他語言支持。協程更適合於用來實現彼此熟悉的程序組件，如合作式多任務，叠代器，無限列表和管道。

en.wikipedia.org/wiki/Coroutine

Coroutines are computer-program components that generalize subroutines for non-preemptive multitasking, by allowing multiple entry points for suspending and resuming execution at certain locations. Coroutines are well-suited for implementing familiar program components such as cooperative tasks, exceptions, event loops, iterators, infinite lists and pipes.

Subroutines are special cases of ... coroutines.

—?Donald Knuth.^[3]

yield方式轉移執行權的協程之間不是調用者與被調用者的關系，而是彼此對稱、平等的