SWI-Prolog -- API-function PL_yield

Documentation
- Reference manual
  - Foreign Language Interface
    - The Foreign Include File
      - Argument Passing and Control
        
        Yielding from foreign predicates
        
        PL_yield_address()
        
        PL_can_yield()
- Packages

Availability:C-language interface function

(return) foreign_t PL_yield_address(void *)

Cause PL_next_solution() of the active query to return with PL_S_YIELD. A subsequent call to PL_next_solution() on the same query calls the foreign predicate again with the control status set to PL_RESUME, after which PL_foreign_context_address() retrieves the address passed to this function. The state of the Prolog engine is maintained, including term_t handles. If the passed address needs to be invalidated the predicate must do so when returning either TRUE or FALSE. If the engine terminates the predicate the predicate is called with status PL_PRUNED, in which case the predicate must cleanup.