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   9 \chapter{Finale}%
  10 \label{chp:finale}
  11 \begin{chapterabstract}
  12         This chapter wraps up the monograph by means of:
  13         \begin{itemize}
  14                 \item a conclusion;
  15                 \item an outlook on future work;
  16                 \item an overview of the related work;
  17                 \item and a history of the \gls{MTASK} system.
  18         \end{itemize}
  19 \end{chapterabstract}
  20
  21 \section{Finale}
  22 Traditionally, the \gls{IOT} has been programmed using layered, or tiered, architectures.
  23 Every layer has its own software and hardware characteristics, resulting in semantic friction.
  24 It is hard to orchestrate the smooth cooperation of the individual components, especially during maintenance of the entire \gls{IOT} application.
  25 \Gls{TOP} is a declarative programming paradigm designed to describe multi-tiered interactive systems from a single source.
  26 Such a tierless system prevents the orchestration problems of the tiered approach.
  27 The type system of the host language checks the \gls{ITASK} and \gls{MTASK} components and their interaction.
  28 However, it is not straightforward to run \gls{TOP} systems on resource-constrained devices such as edge devices.
  29
  30 The \gls{MTASK} system bridges this gap by providing a \gls{TOP} programming language for edge devices.
  31 It is a full-fledged \gls{TOP} language hosted in a tiny \gls{FP} language.
  32 Besides the usual \gls{FP} constructs, it contains basic tasks, task combinators, support for sensors and actuators, and interrupts.
  33 It integrates seamlessly into \gls{ITASK}, a \gls{TOP} system for interactive web applications.
  34 In \gls{ITASK}, abstractions are available for the gritty details of interactive web applications such as program distribution, web applications, data storage, and user management.
  35 The \gls{MTASK} system abstracts away all technicalities specific to edge devices such as communication, abstractions for sensors and actuators, interrupts and (multi) task scheduling.
  36 When \gls{MTASK} is used together with \gls{ITASK}, all layers of the \gls{IOT} application are programmed from a single declarative specification (see e.g.\ \cref{sec:home_automation}).
  37
  38 Any device equipped with the \gls{MTASK} \gls{RTS} can be used in the system and dynamically receive tasks for execution.
  39 This domain-specific \gls{OS} only is uploaded once, hence saving precious write cycles on the program memory.
  40 The \gls{MTASK} devices are connected to the \gls{ITASK} system at run time using a single function that takes care of all the communication and error handling.
  41 Once connected to a device, tasks written in the \gls{MTASK} \gls{DSL} can be lifted to \gls{ITASK} tasks.
  42 The tasks are specified and compiled at run time, i.e.\ \gls{CLEAN} can be used as a macro language for constructing \gls{MTASK} tasks, tailor making them for the current work requirements.
  43 When lifted, other tasks in the system can interact with the task through the usual means.
  44 Furthermore, \gls{ITASK} \glspl{SDS} can be lowered to \gls{MTASK} tasks as well, allowing for automatic bidirectional data sharing between \gls{MTASK} tasks and the \gls{ITASK} system irrespective of task relations.
  45
  46 \section{Related work}
  47 The novelties of the \gls{MTASK} system can be compared to existing systems in several categories.
  48 It is an interpreted (\cref{sec:related_int}) \gls{TOP} (\cref{sec:related_top}) \gls{DSL} (\cref{sec:related_dsl}) that may seem similar at first glance to \gls{FRP} (\cref{sec:related_frp}), it is implemented in a functional language (\cref{sec:related_fp}) and due to the execution semantics, multitasking is automatically supported (\cref{sec:related_multi}).
  49 \Cref{sec_t4t:TiredvsTierless} contains an elaborate related work section regarding tierless systems.
  50
  51 \subsection{Interpretation}\label{sec:related_int}
  52 There are a myriad of interpreted programming languages available for more powerful edge devices.
  53 For example, for the popular ESP8266 chip there are ports of \gls{MICROPYTHON}, Lua, BASIC, JavaScript and Lisp.
  54 All of these languages, except the Lisp dialect uLisp (see \cref{sec:related_fp}), are imperative and do not support multitasking out of the box.
  55 They lay pretty hefty constraints on the memory and as a result do not work on smaller microcontrollers.
  56 Another interpretation solution for the tiniest devices is Firmata, a protocol for remotely controlling the microcontroller using a server as the interpreter host \citep{steiner_firmata:_2009}.
  57 \citet{decker_tierless_2015} describes a FlowLog \citep{nelson_tierless_2014} extension to incorporate \gls{IOT} devices into their tierless sytem for software-defined network controllers in a similar way as firmata.
  58 \citet{grebe_haskino:_2016} wrapped Firmata in a remote monad for integration with \gls{HASKELL} that allowed imperative code to be interpreted on the microprocessors.
  59 Later this system was extended to support multithreading as well, stepping away from Firmata as the basis and using their own \gls{RTS} \citep{grebe_threading_2019}.
  60 Both differ from our approach because it is required to mark continuation points by hand and there is no automatic safe data communication.
  61
  62 \Citet{baccelli_reprogramming_2018} provide a single language \gls{IOT} system based on the RIOT \gls{OS} that allows runtime deployment of code snippets called containers.
  63 Both client and server are written in JavaScript.
  64 However, there is no integration between the client and the server other than that they are programmed from a single source.
  65 Mat\`e is an example of a tierless framework for sensor networks where devices run a virtual machine using TinyOS for dynamic provisioning \citep{levis_mate_2002}.
  66
  67 \subsection{DSLs}\label{sec:related_dsl}
  68 Many \glspl{DSL} provide higher-level programming abstractions for microcontrollers, for example providing strong typing or memory safety.
  69 Examples of this are Copilot \citep{hess_arduino-copilot_2020} and Ivory \citep{elliott_guilt_2015}.
  70 Both are imperative \glspl{DSL} embedded in a functional language that compiles to \ccpp{}.
  71
  72 \subsection{Functional programming}\label{sec:related_fp}
  73 \Citet{haenisch_case_2016} showed that there are major benefits to using functional languages on edge devices.
  74 They show that using function languages increased the security and maintainability of the applications.
  75 Traditional implementations of general purpose functional languages have high memory requirements rendering them unuseable for resource-constrained computers.
  76 There have been many efforts to create a general purpose functional language that does fit in small memory environments, albeit with some concessions.
  77 For example, there has been a history of creating tiny Scheme implementations for specific microcontrollers.
  78 It started with BIT \citep{dube_bit:_2000} that only required \qty{64}{\kibi\byte} of memory, followed by {PICBIT} \citep{feeley_picbit:_2003} and {PICOBIT} \citep{st-amour_picobit:_2009} that lowered the memory requirements even more.
  79 \Citet{suchocki_microscheme:_2015} created Microscheme, a functional language targeting \gls{ARDUINO} compatible microcontrollers.
  80 The {*BIT} languages all compile to assembly while Microscheme compiles to \gls{CPP}.
  81 Their implementation leans heavily on \gls{CPP} lambdas, that are available even on \gls{ARDUINO} AVR targets.
  82 An interpreted Lisp implementation called uLisp also exists that runs on microcontrollers as small as the \gls{ARDUINO} {UNO} \citep{johnson-davies_lisp_2020}.
  83
  84 \subsection{Multitasking}\label{sec:related_multi}
  85 Applications for tiny computers are often parallel in nature.
  86 Tasks like reading sensors, watching input devices, operating actuators and maintaining communication are often loosely dependent on each other and are preferably executed in parallel.
  87 Microcontrollers often do not benefit from an \gls{OS} due to memory and processing constraints.
  88 Therefore, writing multitasking applications in an imperative language is possible, but the tasks have to be interleaved by hand \citep{feijs_multi-tasking_2013}.
  89 This results in hard to maintain, error-prone and unscalable spaghetti code.
  90
  91 There are many solutions to overcome this problem in imperative languages.
  92 If the host language is a functional language (e.g.\ the aforementioned scheme variants) multitasking can be achieved without this burden relatively easy using continuation style multiprocessing \citep{wand_continuation-based_1980}.
  93 Writing in this style is complicated and converting an existing program in this continuation passing style results in relatively large programs.
  94 Moreover, there is no built-in thread-safe communication possible between the tasks.
  95 A \gls{TOP} or \gls{FRP} language is superior to manual threading because the programmer is not required to explicitly define continuation points.
  96
  97 Regular preemptive multithreading is too memory intensive for smaller microcontrollers and therefore not suitable.
  98 Manual interleaving of imperative code can be automated to certain extents.
  99 Solutions often require an \gls{RTOS}, have a high memory requirement, do not support local variables, no thread-safe shared memory, no composition, or no events as described in \cref{tbl:multithreadingcompare}.
 100 This table extends the comparison table with \gls{MTASK} in the relevant categories.
 101
 102 \begin{table}
 103         \begin{threeparttable}
 104                 \caption{%
 105                         An overview of imperative multithreading solutions for tiny computers with their relevant characteristics.
 106                         The characteristics are: sequential computing, local variable support, parallel composition, deterministic execution, bounded execution and safe shared memory (adapted from \citet[p.\ 12]{santanna_safe_2013}).
 107                 }\label{tbl:multithreadingcompare}
 108 %               \begin{tabular}{lc>{\columncolor[gray]{0.95}}cc>{\columncolor[gray]{0.95}}cc>{\columncolor[gray]{0.95}}cc}
 109                 \begingroup
 110                 % default is 6pt
 111                 \setlength\tabcolsep{4.5pt}
 112                 \begin{tabular}{lccccccc}
 113                         \toprule
 114                         \multicolumn{2}{c}{Language} & \multicolumn{3}{c}{Complexity} & \multicolumn{3}{c}{Safety}\\
 115                         \midrule
 116                         Name         & Year & SeqCmp    & LocVar    & ParCmp    & DetEx     & BndEx                  & SafeMem\\
 117                         \midrule
 118                         Preemptive   & many & \CIRCLE{} & \CIRCLE{} & \Circle{} & \Circle{} & rt                     & \Circle{}\\
 119                         nesC         & 2003 & \Circle{} & \Circle{} & \Circle{} & \CIRCLE{} & async                  & \Circle{}\\
 120                         OSM          & 2005 & \Circle{} & \CIRCLE{} & \CIRCLE{} & \Circle{} & \Circle{}              & \Circle{}\\
 121                         Protothreads & 2006 & \CIRCLE{} & \Circle{} & \Circle{} & \CIRCLE{} & \Circle{}              & \Circle{}\\
 122                         TinyThreads  & 2006 & \CIRCLE{} & \CIRCLE{} & \Circle{} & \CIRCLE{} & \Circle{}              & \Circle{}\\
 123                         Sol          & 2007 & \CIRCLE{} & \CIRCLE{} & \CIRCLE{} & \CIRCLE{} & \Circle{}              & \Circle{}\\
 124                         FlowTask     & 2011 & \CIRCLE{} & \CIRCLE{} & \Circle{} & \Circle{} & \Circle{}              & \Circle{}\\
 125                         Ocram        & 2013 & \CIRCLE{} & \CIRCLE{} & \Circle{} & \CIRCLE{} & \Circle{}              & \Circle{}\\
 126                         C\'eu        & 2013 & \CIRCLE{} & \CIRCLE{} & \CIRCLE{} & \CIRCLE{} & \CIRCLE{}              & \CIRCLE{}\\
 127                         \gls{MTASK}  & 2022 & \CIRCLE{} & \CIRCLE{} & \CIRCLE{} & \CIRCLE{} & \CIRCLE{}\tnote{1} & \CIRCLE{}\tnote{2}\\
 128                         \bottomrule
 129                 \end{tabular}
 130                 \endgroup
 131                 \begin{tablenotes}
 132                         \item [1] Only for tasks, not for expressions.
 133                         \item [2] Using \glspl{SDS}.
 134                 \end{tablenotes}
 135         \end{threeparttable}
 136 \end{table}
 137
 138 \subsection{Functional reactive programming}\label{sec:related_frp}
 139 The \gls{TOP} paradigm is often compared to \gls{FRP} because they appear similar.
 140 \Gls{FRP} was introduced by \citet{elliott_functional_1997}.
 141 The paradigm strives to make modelling systems safer, more efficient, and composable.
 142 The core concepts are behaviours and events.
 143 A behaviour is a value that varies over time.
 144 Events are happenings in the real world and can trigger behaviours.
 145 Events and behaviours may be combined using combinators.
 146 Tasks in \gls{TOP} are also event driven and can be combined with combinators.
 147 \Gls{TOP} allows for more complex collaboration patterns than \gls{FRP} \citep{wang_maintaining_2018}.
 148 Consequently, \gls{TOP} is unable to provide strong guarantees on memory usage, something \gls{FRP} is capable of.
 149 For example, arrowised \gls{FRP} can give guarantees on upper memory bounds \citep{nilsson_functional_2002}.
 150 The way \gls{FRP}, and for that matter \gls{TOP}, systems are programmed stays close to the design when the domain matches the paradigm.
 151 The \gls{IOT} domain seems to suit this style of programming very well in just the device layer but also for entire \gls{IOT} systems.
 152
 153 For example, Potato is an \gls{FRP} language for building entire \gls{IOT} systems using powerful devices such as the Raspberry Pi leveraging the Erlang \gls{VM} \citep{troyer_building_2018}.
 154 It requires client devices to be able to run the Erlang \gls{VM} which makes it unsuitable for low memory environments.
 155 The emfrp language compiles a \gls{FRP} specification for a microcontroller to \gls{C} code \citep{sawada_emfrp:_2016}.
 156 The \gls{IO} part, the bodies of some functions, still need to be implemented.
 157 These \gls{IO} functions can then be used as signals and combined as in any \gls{FRP} language.
 158 Due to the compilation to \gls{C} it is possible to run emfrp programs on tiny computers.
 159 However, in contrast to in \gls{MTASK}, the tasks are not interpreted and there is no automated communication with a server.
 160 Other examples are CFRP \citep{suzuki_cfrp_2017}, XFRP \citep{shibanai_distributed_2018}, Juniper \citep{helbling_juniper:_2016}, Hailstorm \citep{sarkar_hailstorm_2020}, Haski \citep{valliappan_towards_2020}, arduino-copilot \citep{hess_arduino-copilot_2020}.
 161
 162 \subsection{Task-oriented programming}\label{sec:related_top}
 163 \Gls{TOP} as a paradigm has proven to be effective for implementing distributed, multi-user applications in many domains.
 164 Examples are conference management \citep{plasmeijer_conference_2006}, coastal protection \citep{lijnse_capturing_2011}, incident coordination \citep{lijnse_incidone:_2012}, crisis management \citep{jansen_towards_2010} and telemedicine \citep{van_der_heijden_managing_2011}.
 165 In general, \gls{TOP} results in a higher maintainability, a high separation of concerns, and more effective handling of interruptions of workflow.
 166 \Gls{IOT} applications contain a distributed and multi-user component, but the software on the device mostly follows multiple loosely dependent workflows.
 167 The only other \gls{TOP} language for embedded systems is $\mu$Tasks \citep{piers_task-oriented_2016}.
 168 It is a non-distributed \gls{TOP} \gls{EDSL} hosted in \gls{HASKELL} designed for embedded systems such as payment terminals.
 169 They show that applications tend to be able to cope well with interruptions and are more maintainable.
 170 However, the hardware requirements for running the standard \gls{HASKELL} system are high.
 171
 172 \section{Future work}
 173 There are many ways of extending the research on the \gls{MTASK} system that also concerns \gls{TOP} for resource-constrained devices in general.
 174
 175 \subsection{Security}
 176 The \gls{IOT} has reached the news concerningly many times regarding the lack of security \citep{alhirabi_security_2021}.
 177 The fact that the devices are embedded in the fabric, are hard to reach and thus to update, and can only run limited cryptographic algorithms due to their constrained resources makes security difficult.
 178 The security of \gls{MTASK} and the used protocols are deliberately overlooked at the moment.
 179 The \gls{MTASK} language and \gls{RTS} are modular.
 180 For example, the communication channels are communication method agnostic and operate through a simple duplex channel interface.
 181 It should therefore be fairly easy to apply standard security measures to them by replacing communication methods and applying off-the-shelve authentication and encryption to the protocol.
 182 \Citet{de_boer_secure_2020} did preliminary research on securing the communication channels, which proved to be possible without many changes in the protocol.
 183 Nonetheless, this deserves much more attention.
 184 The future and related work for the security of \gls{MTASK} and tierless systems is more thoroughly presented in \cref{ssec_t4t:security}.
 185
 186 \subsection{Advanced edge devices techniques}
 187 Edge devices produce a lot of data.
 188 It is not always effective to send this data to the server for processing.
 189 Leaving the produced data and computations on the edge device is called edge computing \citep{shi_edge_2016}.
 190 The \gls{MTASK} system exhibits many properties of edge computing because it is possible to run entire workflows on the device.
 191 However, it is interesting to see how far this can be extended.
 192 The \gls{MTASK} language is a high-level \gls{DSL}, so it is obvious to introduce abstractions for edge computations.
 193 For example, add \gls{TOP} support for machine learning on the edge device using TinyML \citep{sanchez-iborra_tinyml-enabled_2020}.
 194 \Citet{van_der_veen_mutable_2020} did preliminary work for embedding bounded datastructures such as arrays to the language.
 195 This could be continued and extended with support for sum types.
 196
 197 Another recent advance in \gls{IOT} edge device programming is battery-less or even battery-free computing.
 198 Instead of equipping the edge device with a battery, a capacitor is used in conjunction with energy harvesting systems such as a solar panel.
 199 After a reset, the program state is resumed from a checkpoint that was stored in some non-volatile memory.
 200 This technique is called intermittent computing \citep{hester_batteries_2019}.
 201 Many intermittent computing solutions rely on annotations from the programmer to divide the program into atomic blocks, sometimes called tasks as well.
 202 These blocks are marked as such, because in the case of a reset of the system, the work must be done again.
 203 Examples of such blocks are \gls{I2C} transmissions or calculations that rely on recent sensor data.
 204 In \gls{MTASK}, all work expressed by tasks is already split up in atomic pieces of work, i.e.\ the work is a side effect of rewriting.
 205 Furthermore, creating checkpoints is fairly straightforward as \gls{MTASK} tasks do not rely on any global state---all information required to execute a task is stored in the task tree.
 206 It is interesting to see what \gls{TOP} abstractions are useful to support intermittent computing properly and what solutions are required to make it work.
 207
 208 Mesh networks allow for communication not only to and fro the device and server but also between devices.
 209 The \gls{ITASK} system already contains primitives for distributed operation.
 210 For example, it is possible to run tasks or share data with \glspl{SDS} on different machines.
 211 It is interesting to investigate how this networking technique can be utilised in \gls{MTASK}.
 212
 213 \Glspl{FPGA} are highly customisable integrated chips consisting of programmable gates.
 214 Promising research has gone into translating purely functional code to \gls{FPGA} configurations \citep{baaij_digital_2015}.
 215 It would be interesting to see how and whether (parts of) \gls{TOP} programs or the functionality of the \gls{MTASK} \gls{OS} could be translated to \gls{FPGA} specifications.
 216
 217 \subsection{Formal semantics}
 218 Semantics allow reasoning about the language and programs in order to do (symbolic) simulation, termination checking, task equivalence, or otherwise.
 219 For \gls{ITASK} there have been two attempts to formally specify the language.
 220 First \citet{koopman_executable_2011} defined a semantics used for property based testing based on a minimal version of \gls{ITASK}.
 221 Then \citet{plasmeijer_task-oriented_2012} formalised \gls{ITASK} by providing an executable semantics for the language.
 222 Both semantics are not suitable for formal reasoning due to the complexity.
 223 Later, \citet{steenvoorden_tophat_2019} created \gls{TOPHAT}, a \gls{TOP} language with a complete formal specification with similar features to \gls{MTASK} \citep{steenvoorden_tophat_2019}.
 224 \Citet{antonova_mtask_2022} compared parts of \gls{MTASK} to the semantics of \gls{TOPHAT} semantics and created a preliminary semantics for a subset of \gls{MTASK}.
 225 Future research into extending the formal semantics of \gls{MTASK} is useful to give more guarantees on \gls{MTASK} programs.
 226
 227 \subsection{Task-oriented programming}
 228 In order to keep the resource constraints low, the \gls{MTASK} language contains only a minimal set of simple task combinators.
 229 From these simple combinators, complex collaboration patterns can be expressed.
 230 The \gls{ITASK} language is designed exactly the opposite.
 231 From just a few super combinators, all other combinators are derived.
 232 However, this approach requires a very powerful host language in which task combinators can be defined in terms of the host language.
 233 It would be fruitful to investigate which workflows cannot be specified with the limited set of combinators available in \gls{MTASK}.
 234 \Citet{van_der_aalst_workflow_2003} defines a benchmark set of workflow patterns.
 235 It is interesting to see which patterns can already be implemented with just \gls{MTASK}, which require a round-trip with the server, and what additional combinators would be needed.
 236
 237 Editors are a crucial part of \gls{TOP}.
 238 In \gls{MTASK}, sensors can be seen as read-only shared editors that are updated by the system.
 239 It is interesting to investigate how actual interactive editors would fit in \gls{MTASK}.
 240 For example, many smartwatches contain touch sensitive screens that could be used to interact with the user in this way.
 241 Alternatively, sufficiently powerful edge devices can probably run simple web interfaces as well.
 242
 243 \Glspl{SDS} in \gls{ITASK} have a rich set of combinators to transform and combine the \glspl{SDS} into new \gls{SDS}.
 244 In \gls{MTASK}, \glspl{SDS} are typed global variables that may or may not proxy an \gls{ITASK} \gls{SDS}.
 245 It could be interesting to port the \gls{SDS} combinators to \gls{MTASK} as well, allowing them to be transformed and combined also.
 246
 247 \subsection{Usability}
 248 The promise of \glspl{DSL} has often been that a domain expert could program with little technical knowledge of the host programming language.
 249 Some even propose that a \gls{DSL} is a \gls{UI} for domain experts to computation platforms \citep{management_association_evaluating_2014}.
 250 In practise this is not always the case due to crippling syntax and convoluted error messages.
 251 Recent approaches in interactive editors for programming language source code such as dynamic editors \citep{koopman_dynamic_2021} or typed tree editors such as Hazelnut \citep{omar_hazelnut_2017} could prove useful for supporting the \gls{DSL} programmer in using \gls{MTASK}.
 252 If the editor produces correct \gls{MTASK} code by construction, much of the problems could be avoided.
 253 In the same respect, as \gls{MTASK} is a tagless-final \gls{EDSL} and uses \gls{HOAS}, the error messages are complex and larded with host language features.
 254 Much research has gone into simplifying these error messages by translating them to the \gls{DSL} domain, see for example the work by \citep{serrano_type_2018}.
 255 \Citet{de_roos_2020} briefly investigated these methods in their research internship.
 256 A future directions could be to extend these findings and apply more \gls{EDSL} error message techniques on \gls{MTASK} as well.
 257
 258 \subsection{Language features}
 259 The serialisation and deserialisation of data types is automated both on the server and the \gls{MTASK} device using generic programming.
 260 Using the structural information of the data type, the code responsible for the functionality is automatically generated.
 261 Peripherals are not yet fully integrated in such a way.
 262 When a peripheral is added, the programmer has to define the correct byte code, implement the instructions in the interpreter, add task tree nodes, and implement them in the rewrite system.
 263 It would be interesting to investigate whether this can be automated or centralised in a way.
 264
 265 More elaborate features in the type systems of modern functional programming languages allow for more type safety.
 266 The \gls{MTASK} language relies a lot on these features such as (multi-parameter) type classes and existential data types with class constraints.
 267 However, it should be possible to make abstractions over an increasing number of features to make it safer still.
 268 For example, the pin mode could be made a type parameter of the \gls{GPIO} pins, or interrupt handling could be made safer by incorporating the capabilities of the devices in order to reduce run-time errors.
 269
 270 \subsection{Scheduling}
 271 The scheduling in \gls{MTASK} works quite well, but it is not real time.
 272 There is a variant of \gls{FRP} called \gls{PFRP} that allows for real-time operation \citep{belwal_variable_2013}.
 273 Furthermore, an alternative to reducing the energy consumption by going to sleep is stepping down the processor frequency.
 274 So called \gls{DVFS} is a scheduling technique that slows down the processor in order to reach the goals as late as possible, reducing the power consumption.
 275 \Citet{belwal_variable_2013} use \gls{PFRP} with \gls{DVFS} to reduce the energy consumption.
 276 It is interesting to investigate the possibilities for \gls{DVFS} in \gls{MTASK} and \gls{TOP} in general.
 277
 278 \section{History of mTask}
 279 The development of \gls{MTASK} or its predecessors has been going on for almost seven years now though it really set off during my master's thesis.
 280 Many colleagues and students have worked on aspects of the \gls{MTASK} system in collaborations, internships and Bachelor and Master's theses.
 281 This section provides an exhaustive overview of the work on \gls{MTASK} and its predecessors.
 282
 283 \subsection{Generating \ccpp{} code}
 284 A first throw at a class-based shallow \gls{EDSL} for microcontrollers was made by \citet{plasmeijer_shallow_2016}.
 285 The language was called \gls{ARDSL} and offered a type safe interface to \gls{ARDUINO} \gls{CPP} dialect.
 286 A \gls{CPP} code generation interpretation was available together with an \gls{ITASK} simulation interpretation.
 287 There was no support for tasks nor functions.
 288 Some time later in the 2015 CEFP summer school, an extended version was created that allowed the creation of imperative tasks, local \glspl{SDS} and the usage of functions \citep{koopman_type-safe_2019}.
 289 The name then changed from \gls{ARDSL} to \gls{MTASK}.
 290
 291 \subsection{Integration with iTask}
 292 \Citet{lubbers_task_2017} extended this in his Master's Thesis by adding integration with \gls{ITASK} and a bytecode compiler to the language.
 293 \Gls{SDS} in \gls{MTASK} could be accessed on the \gls{ITASK} server.
 294 In this way, entire \gls{IOT} systems could be programmed from a single source.
 295 However, this version used a simplified version of \gls{MTASK} without functions.
 296 This was later improved upon by creating a simplified interface where \glspl{SDS} from \gls{ITASK} could be used in \gls{MTASK} and the other way around \citep{lubbers_task_2018}.
 297 It was shown by \citet{amazonas_cabral_de_andrade_developing_2018} that it was possible to build real-life \gls{IOT} systems with this integration.
 298 They did so by creating a functioning prototype of a smart home application.
 299 Moreover, a course on the \gls{MTASK} simulator was provided at the 2018 \gls{3COWS} winter school in Ko\v{s}ice, Slovakia \citep{koopman_simulation_2023}.
 300
 301 \subsection{Transition to Task-oriented programming}
 302 The \gls{MTASK} language as it is now was introduced in 2018 \citep{koopman_task-based_2018}.
 303 This paper updated the language to support functions, simple tasks, and \glspl{SDS} but still compiled to \gls{ARDUINO} \gls{CPP} code.
 304 Later the byte code compiler and \gls{ITASK} integration was added to the language \citep{lubbers_interpreting_2019}.
 305 Moreover, it was shown that it is very intuitive to write microcontroller applications in a \gls{TOP} language \citep{lubbers_multitasking_2019}.
 306 One reason for this is that a lot of design patterns that are difficult using standard means are for free in \gls{TOP} (e.g.\ multithreading).
 307 In 2019, the \gls{3COWS} summer school in Budapest, Hungary hosted a course on developing \gls{IOT} applications with \gls{MTASK} as well \citep{lubbers_writing_2023}.
 308
 309 \subsection{Task-oriented programming}
 310 In 2022, the SusTrainable summer school in Rijeka, Croatia hosted a course on developing greener \gls{IOT} applications using \gls{MTASK} \citep{lubbers_green_2022}.
 311 Several students worked on extending \gls{MTASK} with many useful features:
 312 \citet{van_der_veen_mutable_2020} did preliminary work on a green computing analysis, built a simulator, and explored the possibilities for adding bounded datatypes; de Roos explored beautifying error messages; \citet{de_boer_secure_2020} investigated the possibilities for secure communication channels; \citeauthor{crooijmans_reducing_2021} \citeyearpar{crooijmans_reducing_2021,crooijmans_reducing_2022} added abstractions for low-power operation to \gls{MTASK} such as hardware interrupts and power efficient scheduling; and \citet{antonova_mtask_2022} defined a preliminary formal semantics for a subset of \gls{MTASK}.
 313 In 2023, the SusTrainable summer school in Coimbra, Portugal will host a course on \gls{MTASK}.
 314
 315 \subsection{Using mTask in practice}
 316 Funded by the Radboud-Glasgow Collaboration Fund, collaborative work was executed with Phil Trinder, Jeremy Singer, and Adrian Ravi Kishore Ramsingh.
 317 An existing smart campus application was developed using \gls{MTASK} and quantitatively and qualitatively compared to the original application that was developed using a traditional \gls{IOT} stack \citep{lubbers_tiered_2020}.
 318 This research was later extended to include a four-way comparison: \gls{PYTHON}, \gls{MICROPYTHON}, \gls{ITASK}, and \gls{MTASK} \citep{lubbers_could_2023} (see \cref{chp:smart_campus}).
 319 Currently, power efficiency behaviour of traditional versus \gls{TOP} \gls{IOT} stacks is being compared as well adding a FreeRTOS, and an Elixir implementation to the mix as well.
 320
 321 \input{subfilepostamble}
 322 \end{document}