A simple way to call arbitrary Prolog code is to use
SP_read_from_string()
(see Creating Prolog Terms) to create
an argument to call/1
. It is a good idea to always
explicitly specify the module context when using call/1
or
other meta-predicates from C.
This example calls a compound goal (without error checking):
SP_pred_ref call_pred = SP_predicate("call", 1, "prolog"); SP_term_ref x = SP_new_term_ref(); SP_term_ref goal = SP_new_term_ref(); SP_term_ref vals[] = {x, 0 /* zero termination */}; SP_integer len; SP_put_variable(x); /* The X=_ is a trick to ensure that X is the first variable in the depth-first order and thus corresponds to vals[0] (x). There are no entries in vals for _,L1,L2. */ SP_read_from_string(goal, "user:(X=_, length([0,1,2],L1), length([3,4],L2), X is L1+L2).", vals); SP_query(call_pred, goal); SP_get_integer(x, &len); /* here len is 5 */