Reactive Programming .

• Reactive Programming

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Reactive programming

1 In computing, 'reactive programming' is a programming paradigm oriented

around Dataflow programming|data flows and the propagation of change. This means that it should be possible to

express static or dynamic data flows with ease in the programming languages

used, and that the underlying execution model will automatically propagate

changes through the data flow.



1 In reactive programming, the value of a would be automatically updated based on the new

values.



1 A modern spreadsheet program is an example of reactive programming.

Spreadsheet cells can contain literal values, or formulas such as =B1+C1 that are evaluated based on other cells. Whenever the value of the

other cells change, the value of the formula is automatically updated.



1 Another example is a hardware description language such as Verilog.

In this case reactive programming allows us to model changes as they

propagate through a circuit.



1 Reactive programming has foremost been proposed as a way to simplify

the creation of interactive user interfaces, animations in real time

systems, but is essentially a general programming paradigm.



1 For example, in a Model-view-controller architecture, reactive

programming can allow changes in the underlying model to

automatically be reflected in the view, and vice versa..


Reactive programming - Degrees of explicitness

1 Reactive programming libraries for dynamic languages (such as the Lisp Cells and Python Trellis libraries) can construct a dependency graph from runtime analysis of the values read

during a function's execution, allowing data flow specifications to

be both implicit and dynamic.


Reactive programming - Degrees of explicitness

1 Sometimes the term reactive programming refers to the

architectural level of software engineering, where individual nodes in the data flow graph are ordinary programs that communicate with

each other.


Reactive programming - Static or Dynamic

1 Reactive programming can be purely static where the data flows are set up statically, or be dynamic where the data flows can change during the

execution of a program.


Reactive programming - Static or Dynamic

1 The use of data switches in the data flow graph could to some extent

make a static data flow graph appear as dynamic, and blur the distinction

slightly. True dynamic reactive programming however could use

imperative programming to reconstruct the data flow graph.


Reactive programming - Higher-order reactive programming

1 Reactive programming could be said to be of 'higher order' if it supports the idea that data flows could be

used to construct other data flows. That is, the resulting value out of a data flow is another data flow graph

that is executed using the same evaluation model as the first.


Reactive programming - Data flow differentiation

1 Ideally all data changes are propagated instantly, but this cannot

be assured in practice. Instead it might be necessary to give different parts of the data flow graph different

evaluation priorities. This can be called 'differentiated reactive

programming'.


Reactive programming - Data flow differentiation

1 For example, in a word processor the marking of spelling errors need not be totally in sync with the inserting of characters. Here differentiated

reactive programming could potentially be used to give the spell checker lower priority, allowing it to

be delayed while keeping other data-flows instantaneous.


Reactive programming - Evaluation models of reactive programming

1 One inherent problem for reactive programming is that most

computations that would be evaluated and forgotten in a normal programming language, needs to be represented in the memory as data-

structures. This could potentially make RP highly memory consuming. However, research on what is called lowering could potentially overcome

this problem..https://store.theartofservice.com/the-reactive-programming-toolkit.html

Reactive programming - Evaluation models of reactive programming

1 On the other side, reactive programming is a form of what could be described as explicit parallelism, and could therefore be beneficial for

utilizing the power of parallel hardware.


Reactive programming - Similarities with observer pattern

1 Reactive programming has principal similarities with the observer pattern commonly used in

object-oriented programming. However, integrating the data flow concepts into the

programming language would make it easier to express them, and could therefore increase the granularity of the data flow graph. For example, the observer pattern commonly describes data-flows between whole objects/classes, whereas object-oriented reactive programming could

target the members of objects/classes.


Reactive programming - Imperative

1 It is possible to fuse reactive programming with ordinary imperative programming. In

such a paradigm, imperative programs operate upon reactive data structures.. Such a set-up is analogous to constraint imperative programming; however, while

constraint imperative programming manages bidirectional constraints, reactive imperative programming

manages one-way dataflow constraints.


Reactive programming - Object-oriented

1 Object-oriented reactive programming (OORP) is a combination of object oriented programming and reactive programming.

Perhaps the most natural way to make such a combination is as follows: Instead

of methods and fields, objects have reactions that automatically re-evaluate when the other reactions they depend on have been modified. Below an illustration

of the A=X+Y introductory example:.


Reactive programming - Object-oriented

1 If an OORP programming language maintains its imperative methods, it would also fall under the category of imperative reactive programming.


Reactive programming - Functional

1 Functional reactive programming| Functional reactive programming

(FRP) is a programming paradigm for reactive programming on functional

programming.


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