What is the difference between canceling / 1 and retractall / 1?

Question

From reading the manual, I cannot find the difference between the two.

The manual says:

It is recommended that you use retractall / 1 to erase all dynamic predicate sentences.

So I decided to use retractall/1 in my program; however, I wonder what the difference is.

Answer 1

The standard built-in predicate retractall/1 can be used to remove all sentences for a dynamic predicate, but the predicate will still be known at runtime. On the other hand, the standard built-in predicate abolish/1 not only removes all predicate sentences, but also makes the predicate unknown to the runtime. If you try to call a dynamic predicate after deleting all of your sentences with retractall/1 , the call will simply fail. But if you cancel the dynamic predicate by calling it after this will lead to the error of the existence of the predicate.

Answer 2

Similar to SQL:

retractall(table_name(_,_,_)) can be delete from table_name , while abolish(table_name/3) will play like drop table_name

Answer 3

Before I read your question and @PauloMoura's excellent answer , I didn't know the answer either.

With this answer, I do not want to copy Paulo's answer. Instead, I suggest you consider reading / searching for alternative sources related to Prolog:

• ISO directives, control constructs and built-in functions - iso-prolog on SO

• 4.12.5 Removing items from the database - sicstus-prolog manual

• 8.7 Managing dynamic offers - gnu-prolog manual

• Chapter 9 Dynamic Clauses and Global Variables - bprolog manual

• 6.14 Approval, retraction and other database modifications - xsb manual

• 6.10.1 Database modification - part of the yap manual

Please note that the above may or may not directly correspond to the Prolog that you use .

However, having multiple sources is good: it can prevent you from getting stuck!