The Prolog Programming Language

From a project for the algorithmic treatment of natural language in the 70s Prolog emerged as a declarative programming language.

Under the declarative paradigm, programs are expressed in terms of relations, in the case of Prolog they are composed of Horn clauses, of the type “modus ponendo ponens”, which describe rules such as “If the antecedent is true, then the consequent”.

In Prolog there are no control instructions. Its execution is based on two concepts: unification and backtracking. Thus, an execution is reduced to questioning a question against the rules described.

Through the unification, a set of rules that can be applied are determined, Prolog chooses the first one, repeating the process until it determines if the question is true or false. If it is false, it goes back to the last point of choice, selecting the next applicable rule. There is a set of predefined rules to interact with the system and allow input / output, graphics or communication operations.

Although Prolog was one of the first logic programming languages, it is still popular today, with several implementations available, both free and commercial. Prolog occupies the 26th position in the TIOBE ranking of popularity of programming languages ​​(2021).