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Covariance And Contravariance (computer Science)
Many programming language type systems support subtyping. For instance, if the type (computer science), type is a subtype of , then an expression (computer science), expression of type Liskov_substitution_principle, should be substitutable wherever an expression of type is used. Variance is the category of possible relationships between more composite type, complex types and their components' subtypes. A language's chosen variance determines the relationship between, for example, a list (programming), list of s and a list of s, or a Function (computer science), function return value, returning and a function returning . Depending on the variance of the type constructor, the subtyping relation of the simple types may be either preserved, reversed, or ignored for the respective complex types. In the OCaml programming language, for example, "list of Cat" is a subtype of "list of Animal" because the list type constructor is covariant. This means that the subtyping relation of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Programming Language
A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually defined by a formal language. Languages usually provide features such as a type system, Variable (computer science), variables, and mechanisms for Exception handling (programming), error handling. An Programming language implementation, implementation of a programming language is required in order to Execution (computing), execute programs, namely an Interpreter (computing), interpreter or a compiler. An interpreter directly executes the source code, while a compiler produces an executable program. Computer architecture has strongly influenced the design of programming languages, with the most common type (imperative languages—which implement operations in a specified order) developed to perform well on the popular von Neumann architecture. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Runtime Errors
Execution in computer and software engineering is the process by which a computer or virtual machine interprets and acts on the instructions of a computer program. Each instruction of a program is a description of a particular action which must be carried out, in order for a specific problem to be solved. Execution involves repeatedly following a " fetch–decode–execute" cycle for each instruction done by the control unit. As the executing machine follows the instructions, specific effects are produced in accordance with the semantics of those instructions. Programs for a computer may be executed in a batch process without human interaction or a user may type commands in an interactive session of an interpreter. In this case, the "commands" are simply program instructions, whose execution is chained together. The term run is used almost synonymously. A related meaning of both "to run" and "to execute" refers to the specific action of a user starting (or ''launching'' or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unified Modeling Language
The Unified Modeling Language (UML) is a general-purpose visual modeling language that is intended to provide a standard way to visualize the design of a system. UML provides a standard notation for many types of diagrams which can be roughly divided into three main groups: behavior diagrams, interaction diagrams, and structure diagrams. The creation of UML was originally motivated by the desire to standardize the disparate notational systems and approaches to software design. It was developed at Rational Software in 1994–1995, with further development led by them through 1996. In 1997, UML was adopted as a standard by the Object Management Group (OMG) and has been managed by this organization ever since. In 2005, UML was also published by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) as the ISO/IEC 19501 standard. Since then the standard has been periodically revised to cover the latest revision of UML. In ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Method Overriding
Method overriding, in object-oriented programming, is a language feature that allows a Subclass (computer science), subclass or child class to provide a specific implementation of a Method (computer science), method that is already provided by one of its superclass (computer science), superclasses or parent classes. In addition to providing data-driven algorithm-determined parameters across virtual network interfaces, it also allows for a specific type of Polymorphism_(computer_science), polymorphism (subtyping). The implementation in the subclass overrides (replaces) the implementation in the superclass by providing a method that has same name, same Parameter (computer science), parameters or signature, and same return type as the method in the parent class.Flanagan 2002, p. 107 The version of a method that is executed will be determined by the Object (computer science), object that is used to invoke it. If an object of a parent class is used to invoke the method, then the version ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Higher-order Function
In mathematics and computer science, a higher-order function (HOF) is a function that does at least one of the following: * takes one or more functions as arguments (i.e. a procedural parameter, which is a parameter of a procedure that is itself a procedure), * returns a function as its result. All other functions are ''first-order functions''. In mathematics higher-order functions are also termed '' operators'' or '' functionals''. The differential operator in calculus is a common example, since it maps a function to its derivative, also a function. Higher-order functions should not be confused with other uses of the word "functor" throughout mathematics, see Functor (other). In the untyped lambda calculus, all functions are higher-order; in a typed lambda calculus, from which most functional programming languages are derived, higher-order functions that take one function as argument are values with types of the form (\tau_1\to\tau_2)\to\tau_3. General examples * ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Luca Cardelli
Luca Andrea Cardelli is an Italian computer scientist who is a research professor at the University of Oxford, UK. Cardelli is well known for his research in type theory and operational semantics. Among other contributions, in programming languages, he helped design the language Modula-3, implemented the first compiler for the (non-pure) functional language ML, defined the concept of ''typeful programming'', and helped develop the experimental language Polyphonic C#. Education He was born in Montecatini Terme, Italy. He attended the University of Pisa before receiving his PhD from the University of Edinburgh in 1982 for research supervised by Gordon Plotkin. Career and research Before joining the University of Oxford in 2014, and Microsoft Research in Cambridge, UK in 1997, he worked for Bell Labs and Digital Equipment Corporation, and contributed to Unix software including vismon. Awards and honours In 2004 he was inducted as a Fellow of the Association for Computing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John C
John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Second Epistle of John, often shortened to 2 John * Third Epistle of John, often shortened to 3 John People * John the Baptist (died ), regarded as a prophet and the forerunner of Jesus Christ * John the Apostle (died ), one of the twelve apostles of Jesus Christ * John the Evangelist, assigned author of the Fourth Gospel, once identified with the Apostle * John of Patmos, also known as John the Divine or John the Revelator, the author of the Book of Revelation, once identified with the Apostle * John the Presbyter, a figure either identified with or distinguished from the Apostle, the Evangelist and John of Patmos Other people with the given name Religious figures * John, father of Andrew the Apostle and Saint Peter * Pope John ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rule Of Inference
Rules of inference are ways of deriving conclusions from premises. They are integral parts of formal logic, serving as norms of the Logical form, logical structure of Validity (logic), valid arguments. If an argument with true premises follows a rule of inference then the conclusion cannot be false. ''Modus ponens'', an influential rule of inference, connects two premises of the form "if P then Q" and "P" to the conclusion "Q", as in the argument "If it rains, then the ground is wet. It rains. Therefore, the ground is wet." There are many other rules of inference for different patterns of valid arguments, such as ''modus tollens'', disjunctive syllogism, constructive dilemma, and existential generalization. Rules of inference include rules of implication, which operate only in one direction from premises to conclusions, and rules of replacement, which state that two expressions are equivalent and can be freely swapped. Rules of inference contrast with formal fallaciesinvalid argu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Robustness Principle
In computing, the robustness principle is a design guideline for software that states: "be conservative in what you do, be liberal in what you accept from others". It is often reworded as: "be conservative in what you send, be liberal in what you accept". The principle is also known as Postel's law, after Jon Postel, who used the wording in an early specification of TCP. In other words, programs that send messages to other machines (or to other programs on the same machine) should conform completely to the specifications, but programs that receive messages should accept non-conformant input as long as the meaning is clear. Among programmers, to produce compatible functions, the principle is also known in the form: be contravariant in the input type and covariant in the output type. Interpretation The principle was first written down by Jon Postel in the 1979 IPv4 specification. RFC 1122 (1989) expanded on Postel's principle by recommending that programmers "assume that the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Function Type
In computer science and mathematical logic, a function type (or arrow type or exponential) is the type of a variable or parameter to which a function has or can be assigned, or an argument or result type of a higher-order function taking or returning a function. A function type depends on the type of the parameters and the result type of the function (it, or more accurately the unapplied type constructor , is a higher-kinded type). In theoretical settings and programming languages where functions are defined in curried form, such as the simply typed lambda calculus, a function type depends on exactly two types, the domain ''A'' and the range ''B''. Here a function type is often denoted , following mathematical convention, or , based on there existing exactly (exponentially many) set-theoretic functions mappings ''A'' to ''B'' in the category of sets. The class of such maps or functions is called the exponential object. The act of currying makes the function type adjoint to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
First-class Function
In computer science, a programming language is said to have first-class functions if it treats function (programming), functions as first-class citizens. This means the language supports passing functions as arguments to other functions, returning them as the values from other functions, and assigning them to variables or storing them in data structures. Some programming language theorists require support for anonymous functions (function literals) as well. b) -> [a] -> [b] map f [] = [] map f (x:xs) = f x : map f xs Languages where functions are not first-class often still allow one to write higher-order functions through the use of features such as function pointers or Delegate (CLI), delegates. In the language C (programming language), C: void map(int (*f)(int), int x[], size_t n) There are a number of differences between the two approaches that are ''not'' directly related to the support of first-class functions. The Haskell sample operates on List (computing), lists, w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parametric Polymorphism
In programming languages and type theory, parametric polymorphism allows a single piece of code to be given a "generic" type, using variables in place of actual types, and then instantiated with particular types as needed. Parametrically polymorphic functions and data types are sometimes called generic functions and generic datatypes, respectively, and they form the basis of generic programming. Parametric polymorphism may be contrasted with ad hoc polymorphism. Parametrically polymorphic definitions are ''uniform'': they behave identically regardless of the type they are instantiated at. In contrast, ad hoc polymorphic definitions are given a distinct definition for each type. Thus, ad hoc polymorphism can generally only support a limited number of such distinct types, since a separate implementation has to be provided for each type. Basic definition It is possible to write functions that do not depend on the types of their arguments. For example, the identity function \ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
