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and is read as "Head is true if Body is true". A rule's body consists of calls to predicates, which are called the rule's goals. The built-in predicate,/2 (meaning a 2-arity operator with name ,) denotes conjunction of goals, and ;/2 denotes disjunction. Conjunctions and disjunctions can only appear in the body, not in the head of a rule.
Prolog is a logic programming language that has its origins in artificial intelligence, automated theorem proving and computational linguistics. [1] [2] [3]Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily as a declarative programming language: the program is a set of facts and rules, which define relations.
λProlog, also written lambda Prolog, is a logic programming language featuring polymorphic typing, modular programming, and higher-order programming.These extensions to Prolog are derived from the higher-order hereditary Harrop formulas used to justify the foundations of λProlog.
A rule is called ground if all of its atoms (head and body) are ground. A ground rule R 1 is a ground instance of another rule R 2 if R 1 is the result of a substitution of constants for all the variables in R 2. The Herbrand base of a Datalog program is the set of all ground atoms that can be made with the constants appearing in the program.
Fernando Pereira and David Warren, two other early architects of Prolog, coined the term "definite clause grammar" and created the notation for DCGs that is used in Prolog today. They gave credit for the idea to Colmerauer and Kowalski, and they note that DCGs are a special case of Colmerauer's metamorphosis grammars.
In all of these languages, rules are written in the form of clauses: A :- B 1, ..., B n. and are read as declarative sentences in logical form: A if B 1 and ... and B n. A is called the head of the rule, B 1, ..., B n is called the body, and the B i are called literals or conditions. When n = 0, the rule is called a fact and is written in the ...
This is called a green cut operator.The ! tells the interpreter to stop looking for alternatives; however, if gotmoney(X) fails it will check the second rule. Although checking for gotmoney(X) in the second rule may appear redundant since Prolog's appearance is dependent on gotmoney(X) failing before, otherwise the second rule would not be evaluated in the first place.
Quintus Prolog rose to a de facto standard, and significantly influenced the ISO standard for Prolog developed in 1995/6. [1] In addition, while the module system envisaged by the ISO standard deviates from that of Quintus, the Quintus module system is in fact more widely adopted by modern Prolog implementations than that mandated by ISO. [1]