Node:Cut Overview, Next:, Up:The Cut


One of the more difficult things to master when learning Prolog is the proper use of the cut. Often, when beginners find unexpected backtracking occurring in their programs, they try to prevent it by inserting cuts in a rather random fashion. This makes the programs harder to understand and sometimes stops them from working.

During program development, each predicate in a program should be considered independently to determine whether or not it should be able to succeed more than once. In most applications, many predicates should at most succeed only once; that is, they should be determinate. Having decided that a predicate should be determinate, it should be verified that, in fact, it is. The debugger can help in verifying that a predicate is determinate (see The Determinacy Checker).