Prolog, Mercury and the termination problem

This paper shortly introduces the two logic programming languages Prolog and Mercury. On this background we introduce the problem of analysing termination of programs. Then we present Mercury’s termination analyser, that the authors of the language incorporated into its compiler. We will also discuss the proposition based on the same method analyser for Prolog’s predicates. 1. Prolog Prolog is a logic programming language with its roots in automated theorem proving. Its terminology and concept are based on the first-order predicate logic. There are a few definitions required to understand the rules of programming in Prolog. Facts are used to describe some relations between the objects and they are always true. They consist of relation name, predicate and the list of comaseparated arguments enclosed with brackets. Each fact ends with full stop. For example, the fact expressing the relation of admiration and referring to two objects could have a form like(kate, flowers). Names of used object and predicates must start with lower case letters. The second type of statement in Prolog are rules. Rules comprise two parts, a head and a body connected with ‘:-‘ (neck symbol also read as ‘if’) and end with a full stop. Head is a name of the defined rule with the list of its arguments. Body is a set of goals separated with commas which state for logic ‘and’. That conditional form means that to satisfy the rule it is required for all its goals to succeed. While defining a rule it is allowed to use variables both in its head and body. A variable in Prolog is a string of letters, digits, and underscores beginning either with a capital letter or with an underscore. They are used to replace objects that can not be named at the moment. For example, if we want to describe a person who is a brother of somebody, in Prolog we would use the following form: brother(X,Y) :man(X), parents(O,M,X), parents(O,M,Y). E-mail address: [email protected] Pobrane z czasopisma Annales AIInformatica http://ai.annales.umcs.pl Data: 17/02/2017 10:30:27