eval_to_complete_list(?Collection, ?Result)

Collection

A term to be interpreted as a collection

Result

The collection as list

Description

This is declaratively identical to eval_to_list/2.

The only difference is that the Result argument will only be instantiated once the complete result list (and its length) is known. As long as (subgoals of) eval_to_complete_list/2 delay, the Result variable is not touched. This behaviour makes it easier to write predicates that wait for an input list: they can delay until Result gets instantiated, and then proceed, assuming that Result is a proper, terminated list.

Modes and Determinism

• eval_to_complete_list(?, ?) is semidet

Fail Conditions

Examples

   % Cases with insufficient instantiation:

   ?- eval_to_complete_list(Xs, R).
   R = R
   <delays until result fully known, R not bound>

   ?- eval_to_complete_list([1,2|Xs], R).
   R = R
   <delays until result fully known, R not bound>

   ?- eval_to_complete_list([1,2|Xs], R), Xs=[3].
   R = [1,2,3]
   Yes

   ?- eval_to_complete_list(eval(Xz), R), Xz = [](1,2,3).
   R = [1,2,3]
   Yes

   ?- eval_to_complete_list([1]>>Ys, R).
   R = R
   <delays until result fully known, R not bound>

   ?- eval_to_complete_list([1]>>Ys, R), Ys = [2].
   R = [1,2]
   Yes

   % Other examples see eval_to_list/2

See Also