Bindings resulting from the successful execution of a top-level goal are asserted in a database. These values may be reused in further top-level queries as $Var. Only the latest binding is available. Example:
1 ?- maplist(plus(1), "hello", X).
X = [105,102,109,109,112]
Yes
2 ?- format('~s~n', [$X]).
ifmmp
Yes
3 ?-
| Figure 1 : Reusing top-level bindings |
Note that variables may be set by executing =/2:
6 ?- X = statistics.
X = statistics
Yes
7 ?- $X.
28.00 seconds cpu time for 183,128 inferences
4,016 atoms, 1,904 functors, 2,042 predicates, 52 modules
55,915 byte codes; 11,239 external references
Limit Allocated In use
Heap : 624,820 Bytes
Local stack : 2,048,000 8,192 404 Bytes
Global stack : 4,096,000 16,384 968 Bytes
Trail stack : 4,096,000 8,192 432 Bytes
Yes
8 ?-