reset(Goal,Continuation,Ball). We swapped the argument order for compatibility with catch/3 shift/1 causes reset/3 to return, unifying Continuation with a goal that represents the continuation after shift/1. In other words, meta-calling Continuation completes the execution where shift left it. If Goal does not call shift/1, Continuation are unified with the integer
0(zero).79Note that older versions also unify Ball with
0. Testing whether or not shift happened on Ball however is always ambiguous.