intro/introduction.tex

   1 \documentclass[../thesis.tex]{subfiles}
   2
   3 \input{subfilepreamble}
   4
   5 \begin{document}
   6 \chapter{Prelude}%
   7 \label{chp:introduction}
   8
   9 \begin{chapterabstract}
  10         The sheer number of connected devices around us is mind boggling and seems increases exponentially for many years.
  11         In 2022, there is an estimated number of 13.4 billion of devices connected that sense, act or otherwise interact with the world\footnote{\url{https://transformainsights.com/research/tam/market}, accessed on: \formatdate{2022}{10}{13}}.
  12         These devices, together with the networks that provide the communication, the servers realising the back end and the devices in our pockets are called the \gls{IOT}.
  13         \Gls{IOT} systems can be seen as layered systems, where each layer is powered by different types of computers; and programming languages and paradigms.
  14         Thes thesis shows a novel way of orchestrating these brobdingnagian systems using the \gls{TOP} paradigm.
  15         It does so by giving a proof-of-concept implementation for a \gls{TOP} system specifically designed for the \gls{IOT}: \gls{MTASK}.
  16         At the core of the \gls{MTASK} system is a \gls{DSL}, embedded in the general purpose \gls{TOP} system \gls{ITASK}.
  17         Using the \gls{MTASK} system, all layers of an \gls{IOT} system can be programmed from a single declarative specification.
  18
  19         This chapter provides the required background material, detail regarding the contributions and a reading guide.
  20 \end{chapterabstract}
  21 \todo{Introduction in the abstract doen zoals nu?}
  22
  23 \section{Internet of Things}
  24 The \gls{IOT} is growing rapidly and it is changing the way people and machines interact with the world.
  25 While the term \gls{IOT} briefly gained interest around 1999 to describe the communication of \gls{RFID} devices~\citep{ashton_internet_1999,ashton_that_2009}, it probably already popped up halfway the eigthies in a speech by \citet{peter_t_lewis_speech_1985}:
  26
  27 \begin{quote}
  28         \emph{The \acrlong{IOT}, or \acrshort{IOT}, is the integration of people, processes and technology with connectable devices and sensors to enable remote monitoring, status, manipulation and evaluation of trends of such devices.}
  29 \end{quote}
  30
  31 CISCO states that the \gls{IOT} only started when there where as many connected devices as there were people on the globe, i.e.\ around 2008~\citep{evans_internet_2011}.
  32 Today, the \gls{IOT} is the term for a system of devices that sense the environment, act upon it and communicate with each other and the world.
  33 These connected devices are already in everyone's household in the form of smart electricity meters, smart fridges, smartphones, smart watches, home automation, \etc.
  34
  35 When describing \gls{IOT} systems layered---or tiered---architecture is often used to compartmentalize the technology.
  36 The number of tiers heavily depends on the required complexity of the model but for the intents and purposes of the thesis, the four layer architecture shown in \cref{fig:iot-layers} is used.
  37
  38 \begin{figure}[ht]
  39         \centering
  40         \includestandalone{iot-layers}
  41         \caption{A four-layer \gls{IOT} architecture.}%
  42         \label{fig:iot-layers}
  43 \end{figure}
  44
  45 The presentation layer provides the interface between the user and the \gls{IOT} application.
  46 For example, in home automation, this is a web interface or a mobile app used on the phone or a mounted tablet to interact with the edge devices.
  47
  48 The application layer provides the \glspl{API}, interfaces and data storage.
  49 In home automation, this would be the cloud service or local server.
  50
  51 All layers are connected using the network layer.
  52 In many applications this is implemented using conventional networking techniques such as WiFi or wired networks.
  53 However, networks and layers on top of itt tailored to the needs of \gls{IOT} applications have been increasingly popular such as \gls{BLE}, LoRa, ZigBee, LTE-M, or \gls{MQTT}.
  54
  55 The perception layer---also called edge layer---collects the data, interacts with the environment, and consists of (edge) devices equipped with various sensors and actuators.
  56 %As a special type of device, it may also contain a \gls{SN}.
  57 %A \gls{SN} is a collection of sensors connected by a mesh network or central hub.
  58 In home automation this layer consists of all the microprocessors in the sensors, for example in the smart lightbulbs, actuators to open doors and sensors.
  59
  60 Spanning all layers, the devices are a large heterogeneous collection of different platforms, protocols, paradigms and programming languages resulting in impedance problems or semantic friction between layers~\citep{ireland_classification_2009}.
  61 Furthermore, specifically the perception layer often is a heterogeneous collections of microprocessors in itself as well, each having their own peculiarities, language of choice and hardware interfaces.
  62 As the hardware needs to be cheap, small-scale, and energy efficient, the \glspl{MCU} used to power these devices do not have a lot of computational power, only a soup\c{c}on of memory, and little communication bandwidth.
  63 Typically the devices do not run a full fledged \gls{OS} but a compiled firmware.
  64 This firmware is often written in an imperative language that needs to be flashed to the program memory.
  65 Program memory typically is flash based and only lasts a couple of thousand writes before it wears out.
  66 While devices are getting a bit faster, smaller, and cheaper, they keep these properties to an extent, greatly reducing the flexibility for dynamic systems where tasks are created on the fly, executed on demand, or require parallel execution.
  67 These problems can be mitigated by dynamically sending code to be interpreted to the \gls{MCU}.
  68 With interpretation, a specialized interpreter is flashed in the program memory once that receives the program code to execute at runtime.
  69
  70 %weiser_computer_1991
  71 \section{\texorpdfstring{\Acrlongpl{DSL}}{Domain-specific languages}}
  72 % General
  73 Programming languages can be divided up into two categories: \glspl{DSL}\footnote{Historically this has been called DSEL as well.} and \glspl{GPL}~\citep{fowler_domain_2010}.
  74 Where \glspl{GPL} are not made with a demarcated area in mind, \glspl{DSL} are tailor-made for a specific domain.
  75 Writing idiomatic domain-specific code in an \gls{DSL} is easy but this may come at the cost of the \gls{DSL} being less expressive to an extent that it may not even be Turing complete.
  76 \Glspl{DSL} come in two main flavours: standalone and embedded\footnote{Also called external and internal respectively.} of which \glspl{EDSL} can again be classified into heterogeneous and homogeneous languages (see \cref{fig:hyponymy_of_dsls} for this hyponymy).
  77
  78 \begin{figure}[ht]
  79         \centering
  80         \includestandalone{hyponymy_of_dsls}
  81         \caption{Hyponymy of \glspl{DSL} (adapted from \citet[\citepage{2}]{mernik_extensible_2013})}%
  82         \label{fig:hyponymy_of_dsls}
  83 \end{figure}
  84
  85 \subsection{Standalone and embedded}
  86 \glspl{DSL} where historically created as standalone languages, meaning all the machinery is developed solely for the language.
  87 The advantage of this approach is that the language designer is free to define the syntax and type system of the language as they wish, not being restricted by any constraint.
  88 Unfortunately it also means that they need to develop a compiler or interpreter for the language to be usable making standalone \glspl{DSL} costly to create.
  89 Examples of standalone \glspl{DSL} are regular expressions, make, yacc, XML, SQL, \etc.
  90
  91 A dichotomous approach is embedding the \gls{DSL} in a host language, i.e.\ \glspl{EDSL}~\citep{hudak_modular_1998}.
  92 By defining the language as constructs in the host language, much of the machinery is inherited and the cost of creating embedded languages is very low.
  93 There is more linguistic reuse \citep{krishnamurthi_linguistic_2001}.
  94 There are however two sides to the this coin.
  95 If the syntax of the host language is not very flexible, the syntax of the \gls{DSL} may become clumsy.
  96 Furthermore, errors shown to the programmer may be larded with host language errors, making it difficult for a non-expert of the host language to work with the \gls{DSL}.
  97
  98 \subsection{Heterogeneity and homogeneity}
  99 \Citet{tratt_domain_2008} applied a notion from metaprogramming~\citep{sheard_accomplishments_2001} to \glspl{EDSL} to define homogeneity and heterogeneity of \glspl{EDSL} as follows:
 100
 101 \begin{quote}
 102         A homogeneous system is one where all the components are specifically designed to work with each other, whereas in heterogeneous systems at least one of the components is largely, or completely, ignorant of the existence of the other parts of the system.
 103 \end{quote}
 104
 105 Homogeneous \glspl{EDSL} are therefore languages that are solely defined as an extension to their host language.
 106 They often restrict features of the host language to provide a safer interface or capture an idiomatic pattern in the host language for reuse.
 107 The difference between a library and a homogeneous \glspl{EDSL} is not always clear.
 108 Examples of homogeneous \glspl{EDSL} are libraries such as ones for sets, \glspl{GUI} creation, LISP's macro system, \etc.
 109
 110 On the other hand, heterogeneous \glspl{EDSL} are languages that are not executed in the host language.
 111 For example, \citep{elliott_compiling_2003} describe the language Pan, for which the final representation in the host language is a compiler that will, when executed, generate code for a completely different target platform.
 112 In fact, \gls{ITASK} and \gls{MTASK} are both heterogeneous \glspl{EDSL} and \gls{MTASK} specifically is a compiling \gls{DSL}.
 113
 114 \section{Task-oriented programming}
 115 \Gls{TOP} is a declarative programming paradigm designed to model interactive systems~\citep{plasmeijer_task-oriented_2012}.
 116 Instead of dividing problems into layers or tiers, as is done in \gls{IOT} architectures as well, it deals with separation of concerns in a novel way.
 117 From the data types, utilising various \emph{type-parametrised} concepts, all other aspects are handled (see \cref{fig:tosd}).
 118 This approach to software development is called \gls{TOSD}~\citep{wang_maintaining_2018}.
 119
 120 \begin{figure}[ht]
 121         \centering
 122         \begin{subfigure}[t]{.5\textwidth}
 123                 \centering
 124                 \includestandalone{traditional}
 125                 \caption{Traditional layered approach.}
 126         \end{subfigure}%
 127         \begin{subfigure}[t]{.5\textwidth}
 128                 \centering
 129                 \includestandalone{tosd}
 130                 \caption{\Gls{TOSD} approach.}
 131         \end{subfigure}
 132         \caption{Separation of concerns in a traditional setting and in \gls{TOSD} (adapted from \citet[\citesection{1}]{wang_maintaining_2018}).}%
 133         \label{fig:tosd}
 134 \end{figure}
 135
 136 \begin{description}
 137         \item[Presentation layer (\gls{UI})]
 138                 The \gls{UI} of the system is automatically generated from the representation of the type.
 139 %               For instance, \gls{TOP} languages implemented in an \gls{FP} language often use generic programming or template metaprogramming to automatically achieve this.
 140 %               \Gls{TOP} languages embedded in imperative programming languages may use introspection\todo{Do I want this sentence here?}.
 141                 Even though the \gls{UI} is generated from the structure of the datatypes, in practical \gls{TOP} systems it can be tweaked afterwards to suit the specific needs of the application.
 142         \item[Business layer (tasks):]
 143                 A task is an abstract representation of a piece of work that needs to be done.
 144                 It provides an intuitive abstraction over work in the real world.
 145                 Just as with real-life tasks and workflow, tasks can be combined in various ways such as in parallel or in sequence.
 146                 Furthermore, a task is observable which means it is possible to observe a---partial---result during execution and act upon it by for example starting new tasks.
 147                 Examples of tasks are filling in a form, sending an email, reading a sensor or even doing a physical task.
 148         \item[Resource access (\glspl{SDS}):]
 149                 Tasks can communicate using task values but this imposes a problem in many collaboration patterns where tasks that are not necessarily related need to share data.
 150                 Tasks can also share data using \glspl{SDS}, an abstraction over any data.
 151                 An \gls{SDS} can represent typed data stored in a file, a chunk of memory, a database \etc.
 152                 \Glspl{SDS} can also represent external impure data such as the time, random numbers or sensory data.
 153                 Similar to tasks, transformation and combination of \glspl{SDS} is possible.
 154         \item[\Gls{UOD} (programming language):]
 155                 The \gls{UOD} from the business layer is explicitly and separately modelled by the relations that exist in the functions of the host language.
 156 \end{description}
 157
 158 The concept of \gls{TOP} originated from the \gls{ITASK} framework, a declarative workflow language for defining multi-user distributed web applications implemented as an \gls{EDSL} in the lazy pure \gls{FP} language \gls{CLEAN}~\citep{plasmeijer_itasks:_2007,plasmeijer_task-oriented_2012}.
 159 While \gls{ITASK} conceived \gls{TOP}, it is not the only \gls{TOP} language.
 160 \Gls{TOPHAT} is a fully formally specified \gls{TOP} language designed to capture the essence of \gls{TOP} formally~\citep{steenvoorden_tophat_2019}.
 161 \citet{piers_task-oriented_2016} created \textmu{}Task, a \gls{TOP} language for specifying non-interruptible embedded systems implemented as an \gls{EDSL} in \gls{HASKELL}.
 162 \citet{van_gemert_task_2022} created LTasks, a \gls{TOP} language for interactive terminal applications implemented in LUA, a dynamically typed imperative language.
 163 \citet{lijnse_toppyt_2022} created Toppyt, a \gls{TOP} language based on \gls{ITASK}, implemented in \gls{PYTHON}, but designed to be simpler and smaller.
 164 Finally there is \gls{MTASK}, \gls{TOP} language designed for defining workflow for \gls{IOT} devices \citep{koopman_task-based_2018}.
 165 It is written in \gls{CLEAN} as an \gls{EDSL} fully integrated with \gls{ITASK} and allows the programmer to define all layers of an \gls{IOT} system from a single source.
 166
 167 \section{Outline}
 168 Wikipedia defines a rhapsody as follows \citep{wikipedia_contributors_rhapsody_2022}:
 169 \begin{quote}
 170         A \textbf{rhapsody} in music is a one-movement work that is episodic yet integrated, free-flowing in structure, featuring a range of highly contrasted moods, colour, and tonality. An air of spontaneous inspiration and a sense of improvisation make it freer in form than a set of variations.
 171 \end{quote}
 172 This thesis follows the tradition and consists of three movements that are episodic yet integrated, a purely functional rhapsody.
 173 \Cref{prt:dsl} is about \gls{EDSL} techniques, \cref{prt:top} elaborates on \gls{TOP} for the \gls{IOT} and \cref{prt:tvt} compares traditional tiered \gls{IOT} architectures to a tierless architectures such as \gls{TOP}.
 174 The movements are readable independently if the reader is familiarised with the background material provided in \cref{chp:introduction}.
 175 The thesis wraps up with \cref{chp:conclusion} that provides a conclusion and an outlook on future work.
 176
 177 \subsection*{\nameref{prt:dsl}}
 178 This movement is a cumulative---paper-based---movement that focusses on techniques for embedding \glspl{DSL} in \gls{FP} languages.
 179 After reading the first chapter, subsequent chapters in this movement are readable independently.
 180
 181 \subsubsection*{\fullref{chp:dsl_embedding_techniques}}
 182 This chapter outlines the basic \gls{DSL} embedding techniques and compares the properties of several embedding methods.
 183 By example, it provides intuition on shallow embedding, including tagless-final embedding and deep embedding, including deep embedding with \acrshortpl{GADT}.
 184 It is not based on a paper but written as gentle background material for the subsequent chapters in the movement.
 185
 186 \subsubsection*{\fullref{chp:classy_deep_embedding}}
 187 This chapter is based on the paper: \citeentry{lubbers_deep_2022}\todo{change in-press when published}
 188
 189 While supervising \citeauthor{amazonas_cabral_de_andrade_developing_2018}'s \citeyear{amazonas_cabral_de_andrade_developing_2018} Master's thesis, focussing on an early version of \gls{MTASK}, a seed was planted for a novel deep embedding technique for \glspl{DSL} where the resulting language is extendible both in constructs and in interpretation using type classes and existential data types.
 190 Slowly the ideas organically grew to form the technique shown in the paper.
 191
 192 The research from this paper and writing the paper was solely performed by me.
 193 \Cref{sec:classy_reprise} was added after publication and contains a (yet) unpublished extension of the embedding technique.
 194 The related work section (\cref{sec:cde:related}) is also brought up to date.\todo{weghalen als dit niet het geval is}
 195
 196 \subsubsection*{\fullref{chp:first-class_datatypes}}
 197 This chapter is based on the paper: \citeentry{lubbers_first-class_2022}\todo{change when accepted}
 198
 199 When embedding \glspl{DSL} many features of the host language can be inherited.
 200 However, data types from the host are not first-class citizens, in order to use the datatypes, access functions need to be created in the \gls{DSL} resulting in boilerplate.
 201 This paper shows how to inherit data types from the host language in \glspl{EDSL} using metaprogramming by generating the boilerplate required.
 202
 203 The research in this paper and writing the paper was performed by me, though there were weekly meetings with Pieter Koopman and Rinus Plasmeijer in which we discussed and refined the ideas.
 204
 205 \subsection*{\nameref{prt:top}}
 206 This part is a monograph focussing on \glspl{TOP} for the \gls{IOT} and hence are the chapters best read in order.
 207 The monograph is compiled from the following papers and revised lecture notes.
 208
 209 \begin{itemize}
 210         \item \citeentry{koopman_task-based_2018}
 211
 212                 While an imperative predecessor of \gls{MTASK} was conceived in 2017 \citep{plasmeijer_shallow_2016}, this paper showed the first \gls{TOP} version of \gls{MTASK}.
 213                 It shows the design of the language and three intepretations: pretty printing, simulation using \gls{ITASK} and \gls{C} code generation.
 214                 Pieter Koopman wrote the paper, I helped with the software and research.
 215         \item \citeentry{lubbers_task_2018}
 216
 217                 This paper was an extension of my Master's thesis~\citep{lubbers_task_2017}.
 218                 It shows how a simple imperative variant of \gls{MTASK} was integrated with \gls{ITASK}.
 219                 While the language was a lot different than later versions, the integration mechanism is still used in \gls{MTASK} today.
 220                 The research in this paper and writing the paper was performed by me, though there were weekly meetings with Pieter Koopman and Rinus Plasmeijer in which we discussed and refined the ideas.
 221         \item \citeentry{lubbers_multitasking_2019}
 222
 223                 This paper was a short paper on the multitasking capabilities of \gls{MTASK} in contrast to traditional multitasking methods for \gls{ARDUINO}.
 224                 The research in this paper and writing the paper was performed by me, though there were weekly meetings with Pieter Koopman and Rinus Plasmeijer.
 225         \item \citeentry{koopman_simulation_2018}\todo{change when published}
 226
 227                 These revised lecture notes are from a course on the \gls{MTASK} simulator was provided at the 2018 CEFP/3COWS winter school in Ko\v{s}ice, Slovakia.
 228
 229                 Pieter Koopman wrote and taught it, I helped with the software and research.
 230         \item \citeentry{lubbers_writing_2019}\todo{change when published}
 231
 232                 These revised lecture notes are from a course on programming in \gls{MTASK} provided at the 2019 CEFP/3COWS summer school in Budapest, Hungary.
 233
 234                 Pieter Koopman prepared and taught half of the lecture and supervised the practical session.
 235                 I taught the other half of the lecture, wrote the lecture notes, made the assignments and supervised the practical session.
 236         \item \citeentry{lubbers_interpreting_2019}
 237
 238                 This paper shows an implementation for \gls{MTASK} for microcontrollers in the form of a compilation scheme and informal semantics description.
 239
 240                 The research in this paper and writing the paper was performed by me, though there were weekly meetings with Pieter Koopman and Rinus Plasmeijer.
 241         \item \citeentry{crooijmans_reducing_2022}\todo{change when published}
 242
 243                 This paper shows how to create a scheduler so that devices running \gls{MTASK} tasks can go to sleep more automatically.
 244                 Furthermore, it shows how to integrate hardware interrupts into \gls{MTASK}.
 245                 The research was carried out by \citet{crooijmans_reducing_2021} during his Master's thesis.
 246                 I did the daily supervision and helped with the research, Pieter Koopman was the formal supervisor and wrote most of the paper.
 247         \item \emph{Green Computing for the Internet of Things}\todo{change when published}
 248
 249                 These revised lecture notes are from a course on sustainable programming using \gls{MTASK} provided at the 2022 SusTrainable summer school in Rijeka, Croatia.
 250
 251                 Pieter prepared and taught a quarter of the lecture and supervised the practical session.
 252                 I prepared and taught the other three quarters of the lecture, made the assignments and supervised the practical session\todo{writing contribution}.
 253 \end{itemize}
 254
 255 \subsection*{\nameref{prt:tvt}}
 256 This chapter is based on the journal paper: \citeentry{lubbers_could_2022}\footnote{The journal paper is an extension of the conference article: \citeentry{lubbers_tiered_2020}\footnotemark{}}.
 257 \footnotetext{This paper was partly funded by the Radboud-Glasgow Collaboration Fund.}
 258
 259 It compares programming traditional tiered architectures to tierless architectures by showing a qualitative and a quantitative four-way comparison of a smart campus application.
 260
 261 Writing the paper was performed by all authors.
 262 I created the server application, the \gls{CLEAN}/\gls{ITASK}/\gls{MTASK} implementation (\acrshort{CWS}) and the \gls{CLEAN}/\gls{ITASK} implementation (\acrshort{CRS})
 263 Adrian Ramsingh created the \gls{MICROPYTHON} implementation (\acrshort{PWS}), the original \gls{PYTHON} implementation (\acrshort{PRS}) and the server application were created by Jeremy Singer, Dejice Jacob and Kristian Hentschel~\citep{hentschel_supersensors:_2016}.
 264
 265 \input{subfilepostamble}
 266 \end{document}