Bindings resulting from the successful execution of a top-level goal are asserted in a database if they are not too large. These values may be reused in further top-level queries as $Var. If the same variable name is used in a subsequent query the system associates the variable with the latest binding. Example:
1 ?- maplist(plus(1), `hello`, X).
X = [105,102,109,109,112].
2 ?- format('~s~n', [$X]).
ifmmp
true.
3 ?-
Note that variables may be set by executing =/2:
6 ?- X = statistics. X = statistics. 7 ?- $X. % Started at Fri Aug 24 16:42:53 2018 % 0.118 seconds cpu time for 456,902 inferences % 7,574 atoms, 4,058 functors, 2,912 predicates, 56 modules, 109,791 VM-codes % % Limit Allocated In use % Local stack: - 20 Kb 1,888 b % Global stack: - 60 Kb 36 Kb % Trail stack: - 30 Kb 4,112 b % Total: 1,024 Mb 110 Kb 42 Kb % % 3 garbage collections gained 178,400 bytes in 0.000 seconds. % 2 clause garbage collections gained 134 clauses in 0.000 seconds. % Stack shifts: 2 local, 2 global, 2 trail in 0.000 seconds % 2 threads, 0 finished threads used 0.000 seconds true.