Hacktical C: practical hacker's guide to the C programming language

  #define hc_task_yield(task)   
  do {     
    task->state = __LINE__;   
    return;     
    case __LINE__:;           
  } while (0) 

That's just diabolical. I would not have thought to write "case __LINE__". In the case of a macro, using __LINE__ twice expands to the same value where the macro is used, even if the macro has newlines. It makes sense, but TIL.

With GNU extensions, you can make a simpler coroutine macro without switch/case abuse:

    #define CO_BEGIN static void* cr_state_ = &&cr_st_0; goto *cr_state_; cr_st_0:
    #define CO_RETURN(x) ({ __label__ resume; cr_state_ = &&resume; return (x); resume:; })