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A Beginner’s Guide to Prolog

Logic programming

PROlog is a declarative and logical programming language. It is considered to be one of the fourth-generation programming languages. It supports a declarative paradigm and is appropriate for both symbolic and non-numeric computation. To get started with the language, it is recommended that you have some prior coding experience.

Prolog is a declarative programming language, based on Horn clauses, a subset of first-order logic. It was created in 1972 by Almerauer, Phillipe Roussel, and Robert Kowalski. The name Prolog stands for Programmation en logique. There are several different versions of Prolog.

Prolog is a popular programming language for building intelligent systems. It was originally used in research for natural language processing and later gained a significant following in the artificial intelligence community. It is a declarative language, and logic is represented through relations called Facts and Rules. Running a query over these relations is how computation occurs. If a task fails, Prolog traces back and tries to satisfy a previous task. This process is known as recursion.


Prolog is a logic programming language. It was specified in 1972 and has since undergone numerous refinements. It works by loading and executing code from a file. The language is composed of subprograms, each representing a state of the world. Variables are initialized with capital letters.

Prolog is a procedural language, meaning that it uses truth-functional symbols (TFS). Like predicate calculus, these symbols are interpreted by the same rules as their predicate counterparts. The variable is a string, consisting of lower and upper-case letters, and can contain underscore characters. It is also possible to start a name with a lower-case letter or an upper-case letter. The rules for forming a name are similar to those in predicate calculus.

A valid Prolog term can be input using the read() function. Then, when using the same term in multiple clauses, make sure to use extra parentheses. In addition, use make_set() or nonmember() to add an assertion at the bottom of the search path.

Data structures

When learning a new programming language, one of the first things to learn is about data structures. In Prolog, the basic data structure is a list. Like in Python, lists are made up of multiple elements. Usually, a list has a head and a tail, but they can also be empty.

The standard predicate for reasoning about pairs is keysort/2. This predicate uses the first argument of each pair as the sorting key. However, many Prolog systems also provide additional predicates for reasoning about pairs, such as association lists. These lists are typically based on balanced trees.

To learn about the syntax of data structures in Prolog, one should study examples of how to create them. For example, consider a case where we want to find the smallest key among several elements. This will result in a string that contains the name of the element.


Recursion is a useful feature of Prolog, but it can be difficult to use at first. To explain, think of a family tree, for example. The rules for recursion are ancestor(A, B), parent(A, B), grandparent(A, B), ancestor(A, Z), and child(X, Y). Each of these expressions represents an ancestor of A, B, and Z.

Prolog has two ways of implementing recursion. One way is using the iterative deepening (IDS) search strategy. This technique combines the memory efficiency of depth-first search with the completeness of breadth-first search. Prolog also has a built-in backtracking mechanism for implementing this technique.

Another method is using green cuts, which honor usage patterns. This approach is similar to imperative programming, but with the added benefit of preserving generality. A prolog programmer may want to consider placing recursive elements on the left of the program.


In this Prolog loops tutorial, we’ll examine the concept of prolog loops and how they’re used. In simple terms, a loop in Prolog is a sequence of rules that are applied to a certain situation. Each rule’s body is composed of several pairs of goals. Each pair of goals has a different result so the rule will recursively satisfy each pair of goals.

A Prolog program consists of a database of rules and facts. It doesn’t have a main procedure or nesting of definitions. Variables are global, so the program’s readability is largely up to the programmer.


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