Free
Faster access than browser!

# Type system

In programming languages, a type system is a set of rules that assigns a property called type to the various constructs of a computer program, such as variables, expressions, functions or modules. [1]

## Abstract data type

In computer science, an abstract data type (ADT) is a mathematical model for data types, where a data type is defined by its behavior (semantics) from the point of view of a user of the data, specifically in terms of possible values, possible operations on data of this type, and the behavior of these operations.

## Abstraction (computer science)

In software engineering and computer science, abstraction is.

## ACM Computing Surveys

ACM Computing Surveys (CSUR) is a peer reviewed scientific journal published by the Association for Computing Machinery.

## Alex Martelli

Alex Martelli (born October 5, 1955) is an Italian computer engineer and Fellow of the Python Software Foundation.

## Algebraic data type

In computer programming, especially functional programming and type theory, an algebraic data type is a kind of composite type, i.e., a type formed by combining other types.

## Array data structure

In computer science, an array data structure, or simply an array, is a data structure consisting of a collection of elements (values or variables), each identified by at least one array index or key.

## Assignment (computer science)

In computer programming, an assignment statement sets and/or re-sets the value stored in the storage location(s) denoted by a variable name; in other words, it copies a value into the variable.

## Association for Computing Machinery

The Association for Computing Machinery (ACM) is an international learned society for computing.

## Associative array

In computer science, an associative array, map, symbol table, or dictionary is an abstract data type composed of a collection of (key, value) pairs, such that each possible key appears at most once in the collection.

## Bit

The bit (a portmanteau of binary digit) is a basic unit of information used in computing and digital communications.

## Bounds checking

In computer programming, bounds checking is any method of detecting whether a variable is within some bounds before it is used.

## Brian Kernighan

Brian Wilson Kernighan (born January 1, 1942) is a Canadian computer scientist who worked at Bell Labs alongside Unix creators Ken Thompson and Dennis Ritchie and contributed to the development of Unix.

## C (programming language)

C (as in the letter ''c'') is a general-purpose, imperative computer programming language, supporting structured programming, lexical variable scope and recursion, while a static type system prevents many unintended operations.

## C Sharp (programming language)

C# (/si: ʃɑːrp/) is a multi-paradigm programming language encompassing strong typing, imperative, declarative, functional, generic, object-oriented (class-based), and component-oriented programming disciplines.

## C++

C++ ("see plus plus") is a general-purpose programming language.

## Character (computing)

In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language.

## Class (computer programming)

In object-oriented programming, a class is an extensible program-code-template for creating objects, providing initial values for state (member variables) and implementations of behavior (member functions or methods).

## Clean (programming language)

Clean is a general-purpose purely functional computer programming language.

## Clojure

Clojure (like "closure") is a dialect of the Lisp programming language.

## Code coverage

In computer science, test coverage is a measure used to describe the degree to which the source code of a program is executed when a particular test suite runs.

## Common Lisp

Common Lisp (CL) is a dialect of the Lisp programming language, published in ANSI standard document ANSI INCITS 226-1994 (R2004) (formerly X3.226-1994 (R1999)).

## Comparison of programming languages by type system

This comparison of programming languages (type system) compares the features of type systems or their type checking for multiple programming languages.

## Compile time

In computer science, compile time refers to either the operations performed by a compiler (the "compile-time operations"), programming language requirements that must be met by source code for it to be successfully compiled (the "compile-time requirements"), or properties of the program that can be reasoned about during compilation.

## Compiler

A compiler is computer software that transforms computer code written in one programming language (the source language) into another programming language (the target language).

## Computer

A computer is a device that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming.

## Computer memory

In computing, memory refers to the computer hardware integrated circuits that store information for immediate use in a computer; it is synonymous with the term "primary storage".

## Computer program

A computer program is a collection of instructions for performing a specific task that is designed to solve a specific class of problems.

## Correctness (computer science)

In theoretical computer science, correctness of an algorithm is asserted when it is said that the algorithm is correct with respect to a specification.

## Coupling (computer programming)

In software engineering, coupling is the degree of interdependence between software modules; a measure of how closely connected two routines or modules are;ISO/IEC/IEEE 24765:2010 Systems and software engineering — Vocabulary the strength of the relationships between modules.

## Covariance and contravariance (computer science)

Many programming language type systems support subtyping.

## Cython

Cython is a superset of the Python programming language, designed to give C-like performance with code that is written mostly in Python.

## Data type

In computer science and computer programming, a data type or simply type is a classification of data which tells the compiler or interpreter how the programmer intends to use the data.

## Decidability (logic)

In logic, the term decidable refers to the decision problem, the question of the existence of an effective method for determining membership in a set of formulas, or, more precisely, an algorithm that can and will return a boolean true or false value that is correct (instead of looping indefinitely, crashing, returning "don't know" or returning a wrong answer).

## Dependent ML

Dependent ML is an experimental functional programming language proposed by Hongwei Xi and Frank Pfenning.

## Dependent type

In computer science and logic, a dependent type is a type whose definition depends on a value.

## Disjoint union

In set theory, the disjoint union (or discriminated union) of a family of sets is a modified union operation that indexes the elements according to which set they originated in.

## Division by zero

In mathematics, division by zero is division where the divisor (denominator) is zero.

## Documentation

Documentation is a set of documents provided on paper, or online, or on digital or analog media, such as audio tape or CDs.

## Downcasting

In class-based programming, downcasting or type refinement is the act of casting a reference of a base class to one of its derived classes.

## Duck test

The duck test is a form of abductive reasoning.

## Duck typing

In computer programming, duck typing is an application of the duck test in type safety.

## Dynamic dispatch

In computer science, dynamic dispatch is the process of selecting which implementation of a polymorphic operation (method or function) to call at run time.

## Dynamic programming language

Dynamic programming language, in computer science, is a class of high-level programming languages which, at runtime, execute many common programming behaviors that static programming languages perform during compilation.

## Effect system

In computing, an effect system is a formal system which describes the computational effects of computer programs, such as side effects.

## Empirical evidence

Empirical evidence, also known as sensory experience, is the information received by means of the senses, particularly by observation and documentation of patterns and behavior through experimentation.

## Epigram (programming language)

Epigram is a functional programming language with dependent types.

## Eval

In some programming languages, eval is a function which evaluates a string as though it were an expression and returns a result; in others, it executes multiple lines of code as though they had been included instead of the line including the eval.

## Existential quantification

In predicate logic, an existential quantification is a type of quantifier, a logical constant which is interpreted as "there exists", "there is at least one", or "for some".

## Expression (computer science)

An expression in a programming language is a combination of one or more constants, variables, operators, and functions that the programming language interprets (according to its particular rules of precedence and of association) and computes to produce ("to return", in a stateful environment) another value.

## Extended static checking

Extended static checking (ESC) is a collective name for a range of techniques for statically checking the correctness of various program constraints.

## F Sharp (programming language)

F# (pronounced F sharp) is a strongly typed, multi-paradigm programming language that encompasses functional, imperative, and object-oriented programming methods.

## Floating-point arithmetic

In computing, floating-point arithmetic is arithmetic using formulaic representation of real numbers as an approximation so as to support a trade-off between range and precision.

## Formal language

In mathematics, computer science, and linguistics, a formal language is a set of strings of symbols together with a set of rules that are specific to it.

## Formal methods

In computer science, specifically software engineering and hardware engineering, formal methods are a particular kind of mathematically based techniques for the specification, development and verification of software and hardware systems.

## Formal verification

In the context of hardware and software systems, formal verification is the act of proving or disproving the correctness of intended algorithms underlying a system with respect to a certain formal specification or property, using formal methods of mathematics.

## Generalized algebraic data type

In functional programming, a generalized algebraic data type (GADT, also first-class phantom type, guarded recursive datatype, or equality-qualified type) is a generalization of parametric algebraic data types.

## Generic programming

Generic programming is a style of computer programming in which algorithms are written in terms of types to-be-specified-later that are then instantiated when needed for specific types provided as parameters.

Gilad Bracha is the creator of the Newspeak programming language, a software engineer at Google and a member of the Dart (programming language) team.

## Gordon Plotkin

Gordon David Plotkin, FRS, FRSE (born 9 September 1946) is a theoretical computer scientist in the School of Informatics at the University of Edinburgh.

Gradual typing is a type system in which some variables and expressions may be given types and the correctness of the typing is checked at compile-time (which is static typing) and some expressions may be left untyped and eventual type errors are reported at run-time (which is dynamic typing).

## Halting problem

In computability theory, the halting problem is the problem of determining, from a description of an arbitrary computer program and an input, whether the program will finish running (i.e., halt) or continue to run forever.

Haskell is a standardized, general-purpose compiled purely functional programming language, with non-strict semantics and strong static typing.

## IEEE 754 revision

IEEE 754-2008 (previously known as IEEE 754r) was published in August 2008 and is a significant revision to, and replaces, the IEEE 754-1985 floating point standard.

## Immutable object

In object-oriented and functional programming, an immutable object (unchangeable object) is an object whose state cannot be modified after it is created.

## Infinite loop

An infinite loop (or endless loop) is a sequence of instructions in a computer program which loops endlessly, either due to the loop having no terminating condition, having one that can never be met, or one that causes the loop to start over.

## Instruction set architecture

An instruction set architecture (ISA) is an abstract model of a computer.

## Integer

An integer (from the Latin ''integer'' meaning "whole")Integer&#x2009;'s first literal meaning in Latin is "untouched", from in ("not") plus tangere ("to touch").

## Interface (computing)

In computing, an interface is a shared boundary across which two or more separate components of a computer system exchange information.

## Interpreter (computing)

In computer science, an interpreter is a computer program that directly executes, i.e. performs, instructions written in a programming or scripting language, without requiring them previously to have been compiled into a machine language program.

## James Whitcomb Riley

James Whitcomb Riley (October 7, 1849 – July 22, 1916) was an American writer, poet, and best-selling author.

## Java (programming language)

Java is a general-purpose computer-programming language that is concurrent, class-based, object-oriented, and specifically designed to have as few implementation dependencies as possible.

## JavaScript

JavaScript, often abbreviated as JS, is a high-level, interpreted programming language.

## John C. Mitchell

John Clifford Mitchell is professor of computer science and (by courtesy) electrical engineer at Stanford University.

## Kind (type theory)

In the area of mathematical logic and computer science known as type theory, a kind is the type of a type constructor or, less commonly, the type of a higher-order type operator.

## Late binding

Late binding, or dynamic binding, is a computer programming mechanism in which the method being called upon an object or the function being called with arguments is looked up by name at runtime.

## Linear logic

Linear logic is a substructural logic proposed by Jean-Yves Girard as a refinement of classical and intuitionistic logic, joining the dualities of the former with many of the constructive properties of the latter.

## Lint (software)

A linter or lint refers to tools that analyze source code to flag programming errors, bugs, stylistic errors, and suspicious constructs.

## Liskov substitution principle

Substitutability is a principle in object-oriented programming stating that, in a computer program, if S is a subtype of T, then objects of type T may be replaced with objects of type S (i.e. an object of type T may be substituted with any object of a subtype S) without altering any of the desirable properties of the program (correctness, task performed, etc.). More formally, the Liskov substitution principle (LSP) is a particular definition of a subtyping relation, called (strong) behavioral subtyping, that was initially introduced by Barbara Liskov in a 1987 conference keynote address titled Data abstraction and hierarchy.

## Logic error

In computer programming, a logic error is a bug in a program that causes it to operate incorrectly, but not to terminate abnormally (or crash).

In computing, a memory address is a reference to a specific memory location used at various levels by software and hardware.

## Memory safety

Memory safety is the state of being protected from various software bugs and security vulnerabilities when dealing with memory access, such as buffer overflows and dangling pointers.

## Metaclass

In object-oriented programming, a metaclass is a class whose instances are classes.

## Metaprogramming

Metaprogramming is a programming technique in which computer programs have the ability to treat programs as their data.

## Method (computer programming)

A method in object-oriented programming (OOP) is a procedure associated with a message and an object.

## Microsoft

Microsoft Corporation (abbreviated as MS) is an American multinational technology company with headquarters in Redmond, Washington.

## Microsoft Developer Network

Microsoft Developer Network (MSDN) is the portion of Microsoft responsible for managing the firm's relationship with developers and testers, such as hardware developers interested in the operating system (OS), and software developers developing on the various OS platforms or using the API or scripting languages of Microsoft's applications.

## ML (programming language)

ML (Meta Language) is a general-purpose functional programming language.

## Mock object

In object-oriented programming, mock objects are simulated objects that mimic the behavior of real objects in controlled ways.

## Modular programming

Modular programming is a software design technique that emphasizes separating the functionality of a programme into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect of the desired functionality.

## Multiple dispatch

Multiple dispatch or multimethods is a feature of some programming languages in which a function or method can be dynamically dispatched based on the run-time (dynamic) type or, in the more general case some other attribute, of more than one of its arguments.

## Nominal type system

In computer science, a nominal or nominative type system (or name-based type system) is a major class of type system, in which compatibility and equivalence of data types is determined by explicit declarations and/or the name of the types.

## Object (computer science)

In computer science, an object can be a variable, a data structure, a function, or a method, and as such, is a value in memory referenced by an identifier.

## OCaml

OCaml, originally named Objective Caml, is the main implementation of the programming language Caml, created by Xavier Leroy, Jérôme Vouillon, Damien Doligez, Didier Rémy, Ascánder Suárez and others in 1996.

## Opcode

In computing, an opcode (abbreviated from operation code, also known as instruction syllable, instruction parcel or opstring) is the portion of a machine language instruction that specifies the operation to be performed.

## Perl

Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages, Perl 5 and Perl 6.

## Perl 6

Perl 6 is a member of the Perl family of programming languages.

## PHP

PHP: Hypertext Preprocessor (or simply PHP) is a server-side scripting language designed for Web development, but also used as a general-purpose programming language.

## Polymorphism (computer science)

In programming languages and type theory, polymorphism (from Greek πολύς, polys, "many, much" and μορφή, morphē, "form, shape") is the provision of a single interface to entities of different types.

## Presburger arithmetic

Presburger arithmetic is the first-order theory of the natural numbers with addition, named in honor of Mojżesz Presburger, who introduced it in 1929.

## Program analysis

In computer science, program analysis is the process of automatically analyzing the behavior of computer programs regarding a property such as correctness, robustness, safety and liveness.

## Programming language

A programming language is a formal language that specifies a set of instructions that can be used to produce various kinds of output.

## PurifyPlus

PurifyPlus is a memory debugger program used by software developers to detect memory access errors in programs, especially those written in C or C++.

## Python (programming language)

Python is an interpreted high-level programming language for general-purpose programming.

## Racket (programming language)

Racket (formerly PLT Scheme) is a general-purpose, multi-paradigm programming language in the Lisp-Scheme family.

## Record (computer science)

In computer science, a record (also called a structure, struct, or compound data) is a basic data structure.

## Recursive set

In computability theory, a set of natural numbers is called recursive, computable or decidable if there is an algorithm which takes a number as input, terminates after a finite amount of time (possibly depending on the given number) and correctly decides whether the number belongs to the set.

## Referential transparency

Referential transparency and referential opacity are properties of parts of computer programs.

## Refinement (computing)

Refinement is a generic term of computer science that encompasses various approaches for producing correct computer programs and simplifying existing programs to enable their formal verification.

## Reflection (computer programming)

In computer science, reflection is the ability of a computer program to examine, introspect, and modify its own structure and behavior at runtime.

## Ruby (programming language)

Ruby is a dynamic, interpreted, reflective, object-oriented, general-purpose programming language.

## Run time (program lifecycle phase)

In computer science, run time, runtime or execution time is the time during which a program is running (executing), in contrast to other program lifecycle phases such as compile time, link time and load time.

## Scala (programming language)

Scala is a general-purpose programming language providing support for functional programming and a strong static type system.

## Singularity (operating system)

Singularity is an experimental operating system (OS) which was built by Microsoft Research between 2003 and 2010.

## Software bug

A software bug is an error, flaw, failure or fault in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways.

## Software testing

Software testing is an investigation conducted to provide stakeholders with information about the quality of the software product or service under test.

## Static program analysis

Static program analysis is the analysis of computer software that is performed without actually executing programs.

## String (computer science)

In computer programming, a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable.

## Structural type system

A structural type system (or property-based type system) is a major class of type system, in which type compatibility and equivalence are determined by the type's actual structure or definition, and not by other characteristics such as its name or place of declaration.

## Subroutine

In computer programming, a subroutine is a sequence of program instructions that performs a specific task, packaged as a unit.

## Substructural type system

Substructural type systems are a family of type systems analogous to substructural logics where one or more of the structural rules are absent or only allowed under controlled circumstances.

## Subtyping

In programming language theory, subtyping (also subtype polymorphism or inclusion polymorphism) is a form of type polymorphism in which a subtype is a datatype that is related to another datatype (the supertype) by some notion of substitutability, meaning that program elements, typically subroutines or functions, written to operate on elements of the supertype can also operate on elements of the subtype.

## System F

System F, also known as the (Girard–Reynolds) polymorphic lambda calculus or the second-order lambda calculus, is a typed lambda calculus that differs from the simply typed lambda calculus by the introduction of a mechanism of universal quantification over types.

## Template (C++)

Templates are a feature of the C++ programming language that allows functions and classes to operate with generic types.

A trade-off (or tradeoff) is a situational decision that involves diminishing or losing one quality, quantity or property of a set or design in return for gains in other aspects.

## Type inference

Type inference refers to the automatic detection of the data type of an expression in a programming language.

## Type introspection

In computing, type introspection is the ability of a program to examine the type or properties of an object at runtime.

## Type rule

In type theory, a type rule is an inference rule that describes how a type system assigns a type to a syntactic construction.

## Type safety

In computer science, type safety is the extent to which a programming language discourages or prevents type errors.

## Type signature

In computer science, a type signature or type annotation defines the inputs and outputs for a function, subroutine or method.

## Type system

In programming languages, a type system is a set of rules that assigns a property called type to the various constructs of a computer program, such as variables, expressions, functions or modules.

## Type theory

In mathematics, logic, and computer science, a type theory is any of a class of formal systems, some of which can serve as alternatives to set theory as a foundation for all mathematics.

## Typed lambda calculus

A typed lambda calculus is a typed formalism that uses the lambda-symbol (\lambda) to denote anonymous function abstraction.

## Undecidable problem

In computability theory and computational complexity theory, an undecidable problem is a decision problem for which it is known to be impossible to construct a single algorithm that always leads to a correct yes-or-no answer.

## Union type

In computer science, a union is a value that may have any of several representations or formats within the same position in memory; or it is a data structure that consists of a variable that may hold such a value.

## Uniqueness type

In computing, a unique type guarantees that an object is used in a single-threaded way, with at most a single reference to it.

## University of Chicago

The University of Chicago (UChicago, U of C, or Chicago) is a private, non-profit research university in Chicago, Illinois.

## Usenet newsgroup

A Usenet newsgroup is a repository usually within the Usenet system, for messages posted from many users in different locations using Internet.

## Variable (computer science)

In computer programming, a variable or scalar is a storage location (identified by a memory address) paired with an associated symbolic name (an identifier), which contains some known or unknown quantity of information referred to as a value.

## Variant type

Variant is a data type in certain programming languages, particularly Visual Basic, OCaml, Delphi and C++ when using the Component Object Model.

## Visual Basic

Visual Basic is a third-generation event-driven programming language and integrated development environment (IDE) from Microsoft for its Component Object Model (COM) programming model first released in 1991 and declared legacy during 2008.

## Visual Basic .NET

Visual Basic.NET (VB.NET) is a multi-paradigm, object-oriented programming language, implemented on the.NET Framework.

## References

Hey! We are on Facebook now! »