In computing, reactive programming is a declarative programming paradigm concerned with data streams and the propagation of change. With this paradigm, it's possible to express static (e.g., arrays) or dynamic (e.g., event emitters) data streams with ease, and also communicate that an inferred dependency within the associated execution model exists, which facilitates the automatic propagation of the changed data flow. For example, in an imperative programming setting, a := b + c would mean that a is being assigned the result of b + c in the instant the expression is evaluated, and later, the values of b and c can be changed with no effect on the value of a. On the other hand, in reactive programming, the value of a is automatically updated whenever the values of b or c change, without the program having to explicitly re-execute the statement a := b + c to determine the presently assigned value of a. Another example is a hardware description language such as Verilog, where reactive programming enables changes to be modeled as they propagate through circuits. Reactive programming has been proposed as a way to simplify the creation of interactive user interfaces and near-real-time system animation. For example, in a model–view–controller (MVC) architecture, reactive programming can facilitate changes in an underlying model that are reflected automatically in an associated view. Approaches to creating reactive programming languages Several popular approaches are employed in the creation of reactive programming languages. Specification of dedicated languages that are specific to various domain constraints. Such constraints usually are characterized by real-time, embedded computing or hardware description. Another approach involves the specification of general-purpose languages that include support for reactivity. Other approaches are articulated in the definition, and use of programming libraries, or embedded domain-specific languages, that enable reactivity alongside or on top of the programming language. Specification and use of these different approaches results in language capability trade-offs. In general, the more restricted a language is, the more its associated compilers and analysis tools are able to inform developers (e.g., in performing analysis for whether programs are able to execute in actual real time). Functional trade-offs in specificity may result in deterioration of the general applicability of a language. Programming models and semantics A variety of models and semantics govern reactive programming. We can loosely split them along the following dimensions: Synchrony: synchronous versus asynchronous model of time Determinism: deterministic versus non-deterministic evaluation