12.4.18.6 Foreign code and Well Founded Semantics

bool PL_get_delay_list(term_t -dl)

Fetch the current delay list. If this list is not empty, the current answer is undefined. In the logical sense, this function always succeeds and sets dl to the delay list. It returns FALSE if the delay list is empty (and answer is well defined) and TRUE if the delay list is not empty. If dl is 0 no list is instantiated, while the return value is the same. This allows for testing that an answer is undefined as below.

  if ( PL_get_delay_list(0) )
    <undefined>
  else
    <normal answer>

For now, we consider the content of the list elements opaque. See boot/tabling.pl for examples.