A unit type is a mathematical type that allows only one value. At the broadest level, type theory is the branch of mathematics and logic that concerns itself with classifying entities into collections called types. ...

The carrier (underlying set) associated with a unit type can be any singleton set. There is an isomorphism between any two such sets, so it is customary to talk about the unit type and ignore the details of its value. One may also regard the unit type as the type of 0-tuples, i.e. the cartesian product of no types. In mathematics, a singleton is a set with exactly one element. ... In mathematics, an isomorphism (in Greek isos = equal and morphe = shape) is a kind of mapping between objects, devised by Eilhard Mitscherlich, which shows a relation between two properties or operations. ... In mathematics, a tuple is a finite sequence of objects, that is, a list of a limited number of objects (an infinite sequence is a family). ... In mathematics, the Cartesian product (or direct product) X Y of two sets X and Y is the set of all possible ordered pairs whose first component is a member of X and whose second component is a member of Y. This concept is named after Ren Descartes. ...

When applying category theory to types, the unit type is a terminal object in many categories. The unit type should not be confused with the zero or bottom type, which allows no values and is the initial object in many categories. Category theory is a mathematical theory that deals in an abstract way with mathematical structures and relationships between them. ... In mathematics, an initial object of a category C is an object I in C such that to every object X in C, there exists precisely one morphism I → X. The dual notion is that of a terminal object: T is terminal, if to every object X in C there... In mathematics, an initial object of a category C is an object I in C such that to every object X in C, there exists precisely one morphism I → X. The dual notion is that of a terminal object: T is terminal, if to every object X in C there...

Unit type in programming languages

Several computer programming languages provide a unit type to specify the result type of a function with the sole purpose of causing a side effect, and the argument type of a function that does not require arguments. In the functional programming languages ML, Haskell, and Clean, the unit type is called () and its only value is also (), reflecting the 0-tuple interpretation. Computer code (HTML with JavaScript) in a tool that uses Syntax highlighting (colors) to help the developer see the function of each piece of code. ... In computer science, a subroutine (function, procedure, or subprogram) is a sequence of code which performs a specific task, as part of a larger program, and is grouped as one, or more, statement blocks; such code is sometimes collected into software libraries. ... Side-effect can mean: Side-effect (computer science), a state change caused by a function call Adverse drug reaction, an unintended consequence specifically arising from drug therapy Therapeutic effect (medicine), a desirable consequence of any kind of medical treatment, even though resulting as an unintended, unexpected consequence of the treatment... The Haskell programming language logo Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions. ... ML is a general-purpose functional programming language developed by Robin Milner and others in the late 1970s at the University of Edinburgh, whose syntax is inspired by ISWIM. Historically, ML stands for metalanguage as it was conceived to develop proof tactics in the LCF theorem prover (the language of... Haskell logo Haskell is a standardized pure functional programming language with non-strict semantics. ... In computer science Clean is a general-purpose purely functional programming language. ...

In C, C++, C#, and Java, void is a unit type. These languages do not provide any way to declare an object or represent a value with type void. However, this functionality is not needed, since the unit type carries no information. The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language The C programming language is a standardized imperative computer programming language developed in the early 1970s by Dennis Ritchie for use on the Unix operating system. ... C++ (pronounced see plus plus, IPA: ) is a general-purpose computer programming language. ... The title given to this article is incorrect due to technical limitations. ... Java is an object-oriented programming language developed by James Gosling and colleagues at Sun Microsystems in the early 1990s. ... In various programming languages, a void return type indicates that a function does not return a value. ...