The language Prolog was developed in the 1970s. In fact, its origin dates back to at least the 1970s, but it is not commonly known. Its most notable feature is that it is more of a formal language than an informal one. It can be said to have a programming language heritage, especially compared to other languages like Java or C++.
Like other formal languages, Prolog is not expressive enough to allow programmers to write programs without having a prior understanding of the language. Instead, its main purpose is to facilitate a thorough analysis of a particular problem. It is used mainly for analysis of the problems of computer programs, which are difficult or impossible to solve on their own. For example, if a programmer needs to create a tool to generate traffic flow data, he would first have to study the flow of traffic using a historical data set and find a way to analyze this data using the flow analysis language. This is the major difference between the formal programming languages like PLR and those used in industry.
Many of the Prolog programming languages include extensions that allow programmers to use a more powerful formal logic and linguistic tools. Examples of extensions include an extended algebraic approach and a dependency solver. Extensions that allow for more sophisticated and flexible reasoning are usually called “advanced” languages.
Prolog programming is not the only formal language that has been used for analysis of programs. Another popular language is the ML (Natural Language Processing) language, which was created by two computer scientists in the 1960s. The syntax of ML is closer to that of Prolog and the syntax of Prolog is closer to the syntax of ML.
Although there are similarities in syntax, the main differences between ML and Prolog are the fact that ML supports much higher level of formalism and ML’s grammatical structure is less formal. One feature that ML shares with Prolog is the ability to build higher-order functions.
A significant difference between ML and Prolog is that ML doesn’t support user-defined types. The reason behind this is that in order to make a type, an external programmer would need to define it, while in Prolog, the definition of a type is made automatically from the context.
Unlike PLR, ML has no support for user-defined operators. However, users are able to define some standard mathematical operations such as addition, subtraction, multiplication, division, etc. Since there is no built-in way to do these operations, they need to be implemented as external functions that can be accessed by the programmer. For example, a multiplication operator defined in ML can be accessed using multiplication as an external function.
It is important to note that ML is a typed programming language and that there is no way to get a “quick” idea of the type of a term or expression without typing it. If you do not know what an expression looks like, you can refer to the Prolog manual. But unlike in other languages, if you type an expression, it is immediately interpreted as a Prolog term and its type will be shown.
One thing that is common to both PLR and ML is the fact that ML doesn’t support recursion, which is an essential part of Prolog. In Prolog, a simple recursion such as the following is equivalent to the following program:
While in PLR, it is possible to write the above program as
In PLR and ML, you can also have a higher-order function in ML. It is possible to implement a higher-order function in Prolog as a call of an expression that contains a first expression that is followed by a second expression that is followed by a third expression. In this way, a higher-order function is called a “functional extension” of the function and is defined as a function that takes a single argument and produces a single result.