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The syntax and semantics of Prolog, a programming language, are the sets of rules that define how a Prolog program is written and how it is interpreted, respectively.The rules are laid out in ISO standard ISO/IEC 13211 [1] although there are differences in the Prolog implementations.
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.
Each such rule can be read as an implication: … meaning "If each is true, then is true". Logic programs compute the set of facts that are implied by their rules. Many implementations of Datalog, Prolog, and related languages add procedural features such as Prolog's cut operator or extra-logical features such as a foreign function interface.
The first Prolog program, also written in 1972 and implemented in Marseille, was a French question-answering system. The use of Prolog as a practical programming language was given great momentum by the development of a compiler by David H. D. Warren in Edinburgh in 1977.
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.
In fact, the resolution of a goal clause with a definite clause to produce a new goal clause is the basis of the SLD resolution inference rule, used in implementation of the logic programming language Prolog. In logic programming, a definite clause behaves as a goal-reduction procedure.
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.
Negation As Failure has been an important feature of logic programming since the earliest days of both Planner and Prolog. In Prolog, it is usually implemented using Prolog's extralogical constructs. More generally, this kind of negation is known as Weak Negation, [1] [2] in contrast with the strong (i.e. explicit, provable) negation.