4.9 Delimited continuations
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Availability:built-in
Sourcereset(:Goal, ?Ball, -Continuation)
Call Goal. If Goal calls shift/1 and the argument of shift/1 can be unified with Ball,77The argument order described in Schrijvers et al., 2013 is 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).78Note that older versions also unify Ball with 0. Testing whether or not shift happened on Ball however is always ambiguous.