Lesson plan
Cut (logic programming)
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.
Article summary
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.
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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