DOCSLIB.ORG

An Evaluation of Reactive Programming and Promises for Structuring Collaborative Web Applications

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
An Evaluation of Reactive Programming and Promises for Structuring Collaborative Web Applications An Evaluation of Reactive Programming and Promises for Structuring Collaborative Web Applications Kennedy Kambona Elisa Gonzalez Boix Wolfgang De Meuter Software Languages Lab Software Languages Lab Software Languages Lab Vrije Universiteit Brussel Vrije Universiteit Brussel Vrije Universiteit Brussel Brussels, Belgium Brussels, Belgium Brussels, Belgium [email protected] [email protected] [email protected] ABSTRACT gives birth to a variety of challenges. The most notable one JavaScript programs are highly event-driven, resulting in that has recently gained high recognition among JavaScript `asynchronous spaghetti' code that is difficult to maintain enthusiasts is the asynchronous spaghetti[16]: deeply-nested as the magnitude programs written in the language grows. callbacks that have dependencies on data that have been To reduce the effects of this callback hell, various concepts returned from previous asynchronous invocations. have been employed by a number of JavaScript libraries and Since callbacks are common in JavaScript, programmers frameworks. In this paper we investigate the expressive- end up losing the ability to think in the familiar sequential ness of two such techniques, namely reactive extensions and algorithms and end up dealing with an unfamiliar program promises. We have done this by means of a case study con- structure. A program might be forced to shelve program sisting of an online collaborative drawing editor. The editor execution aside and continue when a return value becomes supports advanced drawing features which we try to model available in the unforeseen future while in the meantime ex- using the aforementioned techniques. We then present a ecution continues performing some other computation. This discussion on our overall experience in implementing the ap- structure forces programmers to write their applications in plication using the two concepts. From this, we propose a a nested hierarchy of callbacks, inevitably leading to what roadmap of how to improve support of programming event- is termed as callback hell or the pyramid of doom [21]. driven web applications in JavaScript. In the next sections we present two increasingly popu- lar approaches that have been proposed as a solution to these problems in the JavaScript context: reactive program- Categories and Subject Descriptors ming [9] and the concept of promises [10]. We describe these D.1.5 [Software Programming Techniques]: Object ori- two approaches and apply them on a non-trivial online draw- ented programming; D.3.3 [Programming Languages]: ing application using the standard version of JavaScript, EC- Language Constructs and Features MAScript51. At the same time we also compare the imple- mentations when necessary and observe the lessons learnt Keywords from these experiences. Javascript, Callbacks, Reactive programming, Promises, Event Streams, Behaviours, Futures 2. THE PROBLEM WITH CALLBACKS Callbacks are used in event-driven programming to ob- 1. INTRODUCTION tain results of asynchronous computations. Rather than an JavaScript has been identified as the most dominant lan- application blocking on a potentially indeterministic event, guage in the web [5]. From its conception, the design of the execution semantics of the application shifts from the the JavaScript language was primarily targeted for the web programmer, relinquishing control of the event when the in- browser [17]. As such, the main focus at the time was to vocation happens and registering a method with the intent provide ways to improve user interaction. The language of reacting when the event is performed. therefore provides support for user interaction employing an Utilizing these callbacks in large-scale applications leads event-driven style of programming. to a mix of collocated code fragments that are not easily Though the asynchronous nature of the language lends composable and creates complex flows that force the pro- itself well to building responsive web applications, it also grammer to pass the callbacks around in order to utilize their delayed values as illustrated in Listing 1. In this sce- nario of a chat application, there are three asynchronous calls: the first one registers a user to a chat server (line 1), Permission to make digital or hard copies of all or part of this work for the second asks the server for an available room to join (line personal or classroom use is granted without fee provided that copies are 2) and the third broadcasts an initial chat message (line 3) not made or distributed for profit or commercial advantage and that copies to users in the room. bear this notice and the full citation on the first page. To copy otherwise, to As a result, callbacks become hard to understand, particu- republish, to post on servers or to redistribute to lists, requires prior specific larly when the control flow of an application require handling permission and/or a fee. Dyla ’13, Montpellier, France 1 Copyright 2013 ACM 978-1-4503-2041-2 ...$15.00. As of this writing of multiple events together, or of events that depend on one group of independent asynchronous calls as shown in List- another. The programmer is forced to write boilerplate code ing 3 in the Q library using Q.all. This listing computes in order to orchestrate the asynchronous operations. the Fibonacci of two numbers through promises. Listing 1: Nested Callbacks Listing 3: Composing Promises 1 registerToChatOnServer(username,function(rooms)f 1 fibpromise = Q.all([ 2 joinAvailableRoom(rooms, function(roomname)f 2 computeFibonacci(n−1), 3 sendChatToAll(roomname, msg, function(reply)f 3 computeFibonacci(n−2) 4 showChatReply(reply); 4 ]); 5 g) 5 fibpromise.spread(function (result1, result2 ) f 6 g) 6 //resolver for both operations.. 7 g); 7 console.log( result1 + result2); 8 g),function(err)f 9 //error occurred 3. JAVASCRIPT PROMISES 10 g); One approach to deal with the problem imposed by call- To react to fibpromise we attach a resolver in line 5. The backs has been in the use of promises. In 1976, Daniel Fried- Q library provides Q.spread, which allows the arguments of man and D. Wise [10] originally proposed the term promise the individual elements in a composition to be sent to the as a proxy object that represents an unknown result that is resolver. In this case, fibpromise awaits for both fibonacci yet to be computed. sequences to be computed before it passes the results to the Most implementations regard promises as immutable once- resolving function (line 5) which then sums the results (line resolved promises as per the CommonJS Promises/A spec- 7). ification [12], which states that a promise can be rejected or resolved once and only once, to prevent unanticipated 3.2 Alternative Approaches changes in behaviour. They furthermore encapsulate asy- Within the domain of web development, there exist other nchronous actions, acting much like a value returned from frameworks which provide the abstractions for implemen- the result of a computation only that the value may not tation of promises apart from the Q library. These include be available at the time. Promises therefore represent the AngularJs3, a JavaScript MVC-based framework for web ap- eventual completion and result of a single asynchronous op- plications, and Dart4, a class-based web programming lan- eration. guage. The most common term used for JavaScript promises are The AngularJs promises were inspired by Q and are simi- the thenables, as a developer uses then to attach callbacks lar to Q's promises. However, the functionality provided by to a promise when it is either fulfilled or an exception is AngularJs' promises are a subset to those provided in Q in 2 realised . In line 1 of Listing 2 we use Q.fcall of the order to make them accustomed to the framework's execu- Q [21] library which creates a promise from the returned tion style. It therefore lacks useful features such as promise value of asynchronous invocations. It is important to note chaining. that then also returns a promise, implying that promises can Dart promises (recently re-implemented as Dart futures), be chained together. Listing 2 shows chaining of promises are also similar to Q's promises, with Completers used to (lines 1-4) using the Q library. The listing performs similar manage the futures. Dart also contains a Futures interface functionality as the previous scenario of Listing 1, where pre- for easily creating multiple future objects. We however did defined functions in lines 1-3 perform asynchronous requests not use Dart since the aim of this experiment was to focus to the server. on mainstream technologies, i.e. JavaScript. Dart is a sep- arate specialized language and currently lacks full support Listing 2: .then() in Q for integration with normal JavaScript applications. 1 Q. fcall (registerToChatOnServer) Outside the web, promises are widely employed as abstrac- 2 .then(joinAvailableRoom) tions in the domain of concurrent and distributed languages. 3 .then(sendChat) The distributed, actor-based language AmbientTalk [6] uses 4 .then(function (reply)f similar concepts known as futures for non-blocking remote 5 showChatReply(reply) invocations, which can composed by grouping. Argus [13] 6 g,function (error)f 7 // catch error from all async operations provides promise pipelining, similar to the aforementioned 8 g) promise chaining. Fignale [19] provides future combinators 9 .done(); to compose delayed actions in a scatter/gather pattern. 3.3 Summary 3.1 Composing Promises Promises provide an elegant fall-back from the nested call- In most libraries, promises are
Load more

Recommended publications
  • An Empirical Study on Program Comprehension with Reactive Programming
    Jens Knoop, Uwe Zdun (Hrsg.): Software Engineering 2016, Lecture Notes in Informatics (LNI), Gesellschaft fur¨ Informatik, Bonn 2016 69 An Emirical Study on Program Comrehension with Reactive Programming Guido Salvaneschi, Sven Amann, Sebastian Proksch, and Mira Mezini1 Abstract: Starting from the first investigations with strictly functional languages, reactive programming has been proposed as the programming paradigm for reactive applications. The advantages of designs based on this style overdesigns based on the Observer design pattern have been studied for along time. Over the years, researchers have enriched reactive languages with more powerful abstractions, embedded these abstractions into mainstream languages –including object-oriented languages –and applied reactive programming to several domains, likeGUIs, animations, Webapplications, robotics, and sensor networks. However, an important assumption behind this line of research –that, beside other advantages, reactive programming makes awide class of otherwise cumbersome applications more comprehensible –has neverbeen evaluated. In this paper,wepresent the design and the results of the first empirical study that evaluates the effect of reactive programming on comprehensibility compared to the traditional object-oriented style with the Observer design pattern. Results confirm the conjecture that comprehensibility is enhanced by reactive programming. In the experiment, the reactive programming group significantly outperforms the other group. Keywords: Reactive Programming, Controlled
    [Show full text]
  • The Implementation of Metagraph Agents Based on Functional Reactive Programming
    ______________________________________________________PROCEEDING OF THE 26TH CONFERENCE OF FRUCT ASSOCIATION The Implementation of Metagraph Agents Based on Functional Reactive Programming Valeriy Chernenkiy, Yuriy Gapanyuk, Anatoly Nardid, Nikita Todosiev Bauman Moscow State Technical University, Moscow, Russia [email protected], [email protected], [email protected], [email protected] Abstract—The main ideas of the metagraph data model and there is no doubt that it is the functional approach in the metagraph agent model are discussed. The metagraph programming that makes it possible to make such approach for semantic complex event processing is presented. implementation effectively. Therefore, the work is devoted to The metagraph agent implementation based on Functional the implementation of a multi-agent paradigm using functional Reactive Programming is proposed. reactive programming. The advantage of this implementation is that agents can work in parallel, supporting a functional I. INTRODUCTION reactive paradigm. Currently, models based on complex networks are The article is organized as follows. The section II discusses increasingly used in various fields of science, from the main ideas of the metagraph model. The section III mathematics and computer science to biology and sociology. discusses the metagraph agent model. The section IV discusses According to [1]: “a complex network is a graph (network) the Semantic Complex Event Processing approach and its’ with non-trivial topological features – features that do not occur correspondence to the metagraph model. The section V (which in simple networks such as lattices or random graphs but often is the novel result presented in the article) discusses the occur in graphs modeling of real systems.” The terms “complex metagraph agent implementation based on Functional Reactive network” and “complex graph” are often used synonymously.
    [Show full text]
  • Functional Reactive Programming, Refactored
    Functional Reactive Programming, Refactored Ivan Perez Manuel Barenz¨ Henrik Nilsson University of Nottingham University of Bamberg University of Nottingham [email protected] [email protected] [email protected] Abstract 18] and Reactive Values [21]. Through composition of standard Functional Reactive Programming (FRP) has come to mean many monads like reader, exception, and state, any desirable combination things. Yet, scratch the surface of the multitude of realisations, and of time domain, dynamic system structure,flexible handling of I/O there is great commonality between them. This paper investigates and more can be obtained in an open-ended manner. this commonality, turning it into a mathematically coherent and Specifically, the contributions of this paper are: practical FRP realisation that allows us to express the functionality We define a minimal Domain-Specific Language of causal • of many existing FRP systems and beyond by providing a minimal Monadic Stream Functions (MSFs), give them precise mean- FRP core parametrised on a monad. We give proofs for our theoreti- ing and analyse the properties they fulfill. cal claims and we have verified the practical side by benchmarking We explore the use of different monads in MSFs, how they nat- a set of existing, non-trivial Yampa applications running on top of • our new system with very good results. urally give rise to known reactive constructs, like termination, switching, higher-order, parallelism and sinks, and how to com- Categories and Subject Descriptors D.3.3 [Programming Lan- pose effects at a stream level using monad transformers [15]. guages]: Language Constructs and Features – Control Structures We implement three different FRP variants on top of our frame- • Keywords functional reactive programming, reactive program- work: 1) Arrowized FRP, 2) Classic FRP and 3) Signal/Sink- ming, stream programming, monadic streams, Haskell based reactivity.
    [Show full text]
  • Flapjax: Functional Reactive Web Programming
    Flapjax: Functional Reactive Web Programming Leo Meyerovich Department of Computer Science Brown University [email protected] 1 People whose names should be before mine. Thank you to Shriram Krishnamurthi and Gregory Cooper for ensuring this project’s success. I’m not sure what would have happened if not for the late nights with Michael Greenberg, Aleks Bromfield, and Arjun Guha. Peter Hopkins, Jay McCarthy, Josh Gan, An- drey Skylar, Jacob Baskin, Kimberly Burchett, Noel Welsh, and Lee Butterman provided invaluable input. While not directly involved with this particular project, Kathi Fisler and Michael Tschantz have pushed me along. 1 Contents 4.6. Objects and Collections . 32 4.6.1 Delta Propagation . 32 1. Introduction 3 4.6.2 Shallow vs Deep Binding . 33 1.1 Document Approach . 3 4.6.3 DOM Binding . 33 2. Background 4 4.6.4 Server Binding . 33 2.1. Web Programming . 4 4.6.5 Disconnected Nodes and 2.2. Functional Reactive Programming . 5 Garbage Collection . 33 2.2.1 Events . 6 2.2.2 Behaviours . 7 4.7. Evaluations . 34 2.2.3 Automatic Lifting: Transparent 4.7.1 Demos . 34 Reactivity . 8 4.7.2 Applications . 34 2.2.4 Records and Transparent Reac- 4.8 Errors . 34 tivity . 10 2.2.5 Behaviours and Events: Conver- 4.9 Library vs Language . 34 sions and Event-Based Derivation 10 4.9.1 Dynamic Typing . 34 4.9.2 Optimization . 35 3. Implementation 11 3.1. Topological Evaluation and Glitches . 13 4.9.3 Components . 35 3.1.1 Time Steps . 15 4.9.4 Compilation .
    [Show full text]
  • Computer Science 1
    Computer Science 1 Computer Science Department Website: https://www.cs.uchicago.edu Program of Study The computer science program offers BA and BS degrees, as well as combined BA/MS and BS/MS degrees. Students who earn the BA are prepared either for graduate study in computer science or a career in industry. Students who earn the BS degree build strength in an additional field by following an approved course of study in a related area. The department also offers a minor. Where to Start The Department of Computer Science offers several different introductory pathways into the program. In consultation with their College adviser and the Computer Science Department advisers, students should choose their introductory courses carefully. Some guidelines follow. For students intending to pursue further study in computer science, we recommend CMSC 15100 Introduction to Computer Science I or CMSC 16100 Honors Introduction to Computer Science I as the first course. CMSC 15100 does not assume prior experience or unusually strong preparation in mathematics. Students with programming experience and strong preparation in mathematics should consider CMSC 16100 Honors Introduction to Computer Science I. First-year students considering a computer science major are strongly advised to register for an introductory sequence in the Winter or Spring Quarter of their first year, and it is all but essential that they start the introductory sequence no later than the second quarter of their second year. Students who are not intending to major in computer science, but are interested in getting a rigorous introduction to computational thinking with a focus on applications are encouraged to start with CMSC 12100 Computer Science with Applications I.
    [Show full text]
  • Compiling Real Time Functional Reactive Programming
    Compiling Real Time Functional Reactive Programming Dana N. Xu and Siau-Cheng Khoo Department of Computer Science School of Computing National University of Singapore {xun,khoosc}@comp.nus.edu.sg ABSTRACT 1. INTRODUCTION Most of the past languages for reactive systems are based Reactive systems are required to react in a timely man- on synchronous dataflow. Recently, a new reactive lan- ner to external events. Their use can be found in a broad guage, called Real-Time Functional Reactive Programming range of applications, ranging from high-end consumer prod- (RT-FRP) [18] , has been proposed based on the functional ucts (digital radio, intelligent cookers) to systems used in paradigm. The unique feature of this language is the high- mission-critical applications (such as air-craft and nuclear- level abstraction provided in the form of behaviors for conti- power stations). nuous-time signals, and events for discrete-time signals. RT- Programming these systems poses a great challenge, and FRP also features some performance guarantees in the form a number of programming languages have been proposed of bounded runtime and space usage for each reactive com- over the last two decades. Two main concerns are typically putation step. addressed in these languages. Firstly, some features must In this paper, we propose a new compilation scheme for be available to express signals and events, and how they are RT-FRP. Our compilation scheme is based on two key stages. transformed by the intended reactive systems. Secondly, we In the first stage, we translate RT-FRP program to an in- must be able to show that each reaction could be carried termediate functional code.
    [Show full text]
  • Characterizing Callbacks in Javascript
    Don’t Call Us, We’ll Call You: Characterizing Callbacks in JavaScript Keheliya Gallaba Ali Mesbah Ivan Beschastnikh University of British Columbia University of British Columbia University of British Columbia Vancouver, BC, Canada Vancouver, BC, Canada Vancouver, BC, Canada [email protected] [email protected] [email protected] Abstract—JavaScript is a popular language for developing 1 var db = require(’somedatabaseprovider’); web applications and is increasingly used for both client-side 2 http.get(’/recentposts’, function(req, res){ and server-side application logic. The JavaScript runtime is 3 db.openConnection(’host’, creds, function(err, conn){ inherently event-driven and callbacks are a key language feature. 4 res.param[’posts’]. forEach(function(post) { 5 conn.query(’select * from users where id=’ + post Unfortunately, callbacks induce a non-linear control flow and can [’user’], function(err, results){ be deferred to execute asynchronously, declared anonymously, 6 conn.close(); and may be nested to arbitrary levels. All of these features make 7 res.send(results[0]); callbacks difficult to understand and maintain. 8 }); 9 }); We perform an empirical study to characterize JavaScript 10 }); callback usage across a representative corpus of 138 JavaScript 11 }); programs, with over 5 million lines of JavaScript code. We Listing 1. A representative JavaScript snippet illustrating the comprehension find that on average, every 10th function definition takes a and maintainability challenges associated with nested, anonymous callbacks callback argument, and that over 43% of all callback-accepting and asynchronous callback scheduling. function callsites are anonymous. Furthermore, the majority of callbacks are nested, more than half of all callbacks are asynchronous, and asynchronous callbacks, on average, appear more frequently in client-side code (72%) than server-side (55%).
    [Show full text]
  • Haskell-Like S-Expression-Based Language Designed for an IDE
    Department of Computing Imperial College London MEng Individual Project Haskell-Like S-Expression-Based Language Designed for an IDE Author: Supervisor: Michal Srb Prof. Susan Eisenbach June 2015 Abstract The state of the programmers’ toolbox is abysmal. Although substantial effort is put into the development of powerful integrated development environments (IDEs), their features often lack capabilities desired by programmers and target primarily classical object oriented languages. This report documents the results of designing a modern programming language with its IDE in mind. We introduce a new statically typed functional language with strong metaprogramming capabilities, targeting JavaScript, the most popular runtime of today; and its accompanying browser-based IDE. We demonstrate the advantages resulting from designing both the language and its IDE at the same time and evaluate the resulting environment by employing it to solve a variety of nontrivial programming tasks. Our results demonstrate that programmers can greatly benefit from the combined application of modern approaches to programming tools. I would like to express my sincere gratitude to Susan, Sophia and Tristan for their invaluable feedback on this project, my family, my parents Michal and Jana and my grandmothers Hana and Jaroslava for supporting me throughout my studies, and to all my friends, especially to Harry whom I met at the interview day and seem to not be able to get rid of ever since. ii Contents Abstract i Contents iii 1 Introduction 1 1.1 Objectives ........................................ 2 1.2 Challenges ........................................ 3 1.3 Contributions ...................................... 4 2 State of the Art 6 2.1 Languages ........................................ 6 2.1.1 Haskell ....................................
    [Show full text]
  • Elmulating Javascript
    Linköping University | Department of Computer science Master thesis | Computer science Spring term 2016-07-01 | LIU-IDA/LITH-EX-A—16/042--SE Elmulating JavaScript Nils Eriksson & Christofer Ärleryd Tutor, Anders Fröberg Examinator, Erik Berglund Linköpings universitet SE–581 83 Linköping +46 13 28 10 00 , www.liu.se Abstract Functional programming has long been used in academia, but has historically seen little light in industry, where imperative programming languages have been dominating. This is quickly changing in web development, where the functional paradigm is increas- ingly being adopted. While programming languages on other platforms than the web are constantly compet- ing, in a sort of survival of the fittest environment, on the web the platform is determined by the browsers which today only support JavaScript. JavaScript which was made in 10 days is not well suited for building large applications. A popular approach to cope with this is to write the application in another language and then compile the code to JavaScript. Today this is possible to do in a number of established languages such as Java, Clojure, Ruby etc. but also a number of special purpose language has been created. These are lan- guages that are made for building front-end web applications. One such language is Elm which embraces the principles of functional programming. In many real life situation Elm might not be possible to use, so in this report we are going to look at how to bring the benefits seen in Elm to JavaScript. Acknowledgments We would like to thank Jörgen Svensson for the amazing support thru this journey.
    [Show full text]
  • A Deterministic Model of Concurrent Computation for Reactive Systems by Hendrik Marten Frank Lohstroh a Dissertation S
    Reactors: A Deterministic Model of Concurrent Computation for Reactive Systems by Hendrik Marten Frank Lohstroh A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Computer Science in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Edward A. Lee, Chair Professor Gul A. Agha Professor Alberto L. Sangiovanni-Vincentelli Professor Sanjit A. Seshia Fall 2020 Reactors: A Deterministic Model of Concurrent Computation for Reactive Systems Copyright 2020 by Hendrik Marten Frank Lohstroh i Abstract Reactors: A Deterministic Model of Concurrent Computation for Reactive Systems by Hendrik Marten Frank Lohstroh Doctor of Philosophy in Computer Science University of California, Berkeley Professor Edward A. Lee, Chair Actors have become widespread in programming languages and programming frameworks focused on parallel and distributed computing. While actors provide a more disciplined model for concurrency than threads, their interactions, if not constrained, admit nondeter- minism. As a consequence, actor programs may exhibit unintended behaviors and are less amenable to rigorous testing. The same problem exists in other dominant concurrency mod- els, such as threads, shared-memory models, publish-subscribe systems, and service-oriented architectures. We propose \reactors," a new model of concurrent computation that combines synchronous- reactive principles with a sophisticated model of time to enable determinism while preserving much of the style and performance of actors. Reactors promote modularity and allow for dis- tributed execution. The relationship that reactors establish between events across timelines allows for: 1. the construction of programs that react predictably to unpredictable external events; 2. the formulation of deadlines that grant control over timing; and 3.
    [Show full text]
  • How I Teach Functional Programming
    How I Teach Functional Programming Johannes Waldmann Fakult¨atIMN, HTWK Leipzig, D-04275 Leipzig Abstract. I teach a course Advanced Programming for 4th semester bachelor students of computer science. In this note, I will explain my reasons for choosing the topics to teach, as well as their order, and pre- sentation. In particular, I will show how I include automated exercises, using the Leipzig autotool system. 1 Motivation In my course Advanced Programming, I aim to show mathematical models (say, the lambda calculus) as well as their concrete realization first in its \pure" form in a functional programming language (Haskell [Mar10]), then also in some of today's multi-paradigm languages (imperative and object-oriented, actually mostly class-based) that students already known from their programming courses in their first and second semester. My course is named \advanced" because it introduces functional programming (but it's not advanced functional program- ming). I will explain this in some detail now. Motivation (this section) and discussion will be somewhat opinionated, starting with the following paragraph. I still think it will be clear on what facts my opinion is based, and I hope that at least the facts (examples and exercises) are re-usable by other academic teachers of func- tional programming. The slides for the most recent instance of this lecture are at https://www.imn.htwk-leipzig.de/~waldmann/edu/ss17/fop/folien/, and online exercises can be tried here: https://autotool.imn.htwk-leipzig.de/ cgi-bin/Trial.cgi?lecture=238 When teaching programming, the focus should really be on how to solve the task at hand (given an algorithm, produce executable code) using available tools (programming languages, libraries), and to understand the fundamentals that these tools are based on.
    [Show full text]
  • Reactive Probabilistic Programming
    Reactive Probabilistic Programming Pedro Zuidberg Dos Martires Sebastijan Dumančić KU Leuven KU Leuven [email protected] [email protected] Abstract event might be the delay, and the actor has to reason about Reactive programming allows a user to model the flow of a the possibility of conflicting train routes. program for event-driven streams of data without explicitly stating its control flow. However, many domains are inher- 2 Reactive Probabilistic Programming ently uncertain and observations (the data) might ooze with Reactive programming [1], which falls itself under the declar- noise. Probabilistic programming has emerged as the go-to ative programming paradigm, has recently gained traction as technique to handle such uncertain domains. Therefore, we a paradigm for event-driven applications. A common trait of introduce the concept of reactive probabilistic programming, event driven-applications is that external events at discrete which allows to unify the methods of reactive programming points in time, such as a mouse click from a user on a web and probabilistic programming. Herewith, we broaden the page, drive the execution of a program. The increased inter- scope of probabilistic programming to event-driven data. est has resulted in various implementations, for instance, in Haskell [3] and Scala [5]. Recently also the ReactiveX 2 library Keywords probabilistic programming, reactive program- emerged, with bindings to various different languages. The ming, declarative programming, event-driven data two distinguishing features of reactive programming are: 1 Introduction & Motivation • Behaviors change continuously over time and are com- posable first-class citizens in the reactive programming The declarative programming paradigm allows the user to paradigm.
    [Show full text]