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5.6  Soft Cut

Sometimes it is useful to be able to remove a choice point which is not the last one and to keep the following ones, for example when defining an if-then-else construct which backtracks also into the condition. This functionality is usually called soft cut in the Prolog folklore.

Softcuts are written as:
A *−> B ; C
If A succeeds, B is executed and on backtracking subsequent solutions of A followed by B are returned, but C is never executed. If A fails straight away, C is executed. The behaviour of *−>/2 is similar to −>/2 with the exception that −>/2 cuts both A and the disjunction if A succeeds, whereas *−>/2 cuts only the disjunction.


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