Cancelable Task

Verse from mandeep/VerseMaxxing (Snippets/CancelableTask.verse), by mandeep, under the Apache-2.0 license. Pinned at commit c922eac78. Compile-checked and ready to adapt for UEFN.

• using { /Verse.org/Concurrency }
  using { /UnrealEngine.com/Temporary/Diagnostics }
  
  
  # from Mayapple on the FN Create discord
  CancelableTask<public> := module:
      no_rollback_cancelable<public> := interface:
          Cancel<public>():void
  
      cancelable_task_base<internal> := class<abstract>:
          Task<internal>:task(void)
          CancelEvent<internal>:event()
  
      cancelable_task<public> := class(cancelable_task_base, no_rollback_cancelable):
          Cancel<override>():void=
              CancelEvent.Signal()
  
          Get<public>()<transacts>:task(void) = Task
  
      CancelableFunction<internal>(Function:type{_()<suspends>:any}, CancelEvent:event())<suspends>:void=
          race:
              Function()
              CancelEvent.Await()
  
      CancelableSpawn<public>(Function:type{_()<suspends>:any}):cancelable_task=
          CancelEvent := event(){}
          Task:task(void) = spawn{CancelableFunction(Function, CancelEvent)}