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Prolog is dynamically typed. It has a single data type, the term, which has several subtypes: atoms, numbers, variables and compound terms. An atom is a general-purpose name with no inherent meaning. It is composed of a sequence of characters that is parsed by the Prolog reader as a single unit.
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.
Edinburgh Prolog became the de facto standard and strongly influenced the definition of ISO standard Prolog. Logic programming gained international attention during the 1980s, when it was chosen by the Japanese Ministry of International Trade and Industry to develop the software for the Fifth Generation Computer Systems (FGCS) project.
A definite clause grammar (DCG) is a way of expressing grammar, either for natural or formal languages, in a logic programming language such as Prolog. It is closely related to the concept of attribute grammars / affix grammars. DCGs are usually associated with Prolog, but similar languages such as Mercury also include DCGs.
A prologue or prolog (from Greek πρόλογος prólogos, from πρό pró, "before" and λόγος lógos, "word") is an opening to a story that establishes the context and gives background details, often some earlier story that ties into the main one, and other miscellaneous information.
The exact notation may differ in different Prolog dialects. However, it is always quite simple (no quotations or special beginning characters are necessary). Contrary to many other languages, it is possible to give symbols a meaning by creating some Prolog facts and/or rules.
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 Prolog, =< means "less than or equal to" (as distinct from the arrow <=). In Fortran, operators .LE. and <= both mean "less than or equal to". In Bourne shell and Windows PowerShell, the operator -le means "less than or equal to".