Cut (logic programming)

Feature in Prolog The cut, in Prolog, is a goal, written as !, which always succeeds but cannot be backtracked. Cuts can prevent unwanted backtracking, which could add unwanted solutions and/or space/time overhead to a query. The cut should be used sparingly. While cuts can be inserted into code containing errors, if a test is unnecessary because a cut has guaranteed that it is true, it is good practice to say so in a comment at the appropriate place. Some programmers call the cut a controversial control facility because it was added for efficiency reasons only and is not a logical formula. Types Green cut The use of a cut that only improves efficiency is referred to as a green cut. Green cuts are used to make programs more efficient without changing program output. For example: gamble(X) :- gotmoney(X),!. gamble(X) :- gotcredit(X), \+ gotmoney(X). This is called a green cut operator. The ! tells the interpreter to stop looking for alternatives; however, if gotmoney(X) fails it will check the second rule. Checking for gotmoney(X) in the second rule may appear redundant since Prolog's appearance is dependent on gotmoney(X) failing before, otherwise the second rule would not be evalu