Controlling Backtracking

• Prolog does backtracking by default - this is good - but in certain scenarios it is more efficient to avoid it
• Improves program efficiency and performance
• Ability to control backtracking in situations when it is not really needed
• This is done via a metalevel predicate called the cut
• Affects procedural behaviour of programs by pruning the search tree
• it's use is highly controversial (from software engineering point of view) - as it diminishes the declarative style encouraged by logic programming
• however, widely used - as can greatly improve efficiency

member(X, [ X| _]) :- !.

member(X, [ _| Tail) :-
  member( X, Tail).

Notice the use of the cut in the first clause