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\mychapter{chp:introduction}{Introduction}
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%	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.
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%	Wikipedia~\cite{wikipedia_contributors_rhapsody_2022}
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The sheer number of connected devices around us is increasing exponentially.
First and foremost, these devices are driven by software.
This thesis is about \ldots
\todo[inline]{introduction}

\section{Internet of Things}
\todo[inline]{add more citations and rewrite to make modern}
The \gls{IOT} is growing rapidly and it is changing the way people and machines interact with the world.
While the term \gls{IOT} briefly gained interest around 1999 to describe the communication of \gls{RFID} devices~\todo{cite}, it probably already popped up halfway the eigthies in a speech by Peter T. Lewis~\cite{peter_t_lewis_speech_1985}.

\begin{quote}
	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.
\end{quote}

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~\cite{evans_internet_2011}.
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.
These connected devices are already in everyone's household in the form of smart electricity meters, smart fridges, smartphones, smart watches, home automation, \etc.

When describing \gls{IOT} systems, a layered, or tiered architecture is often used to compartmentalize the technology.
The number of tiers heavily depends on the 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.

\begin{figure}[ht]
	\centering
	\includestandalone{iot-layers}
	\caption{The four layered \gls{IOT} architecture.}%
	\label{fig:iot-layers}
\end{figure}

\begin{description}
	\item[Presentation layer] This presentation layer provides the interface between the user and the \gls{IOT} application.
		For example, in home automation, this is often implemented as a web interface or a mobile app.
	\item[Application layer]
		Servers often power the application layer, by providing the data storage,
		One of its goals is to provide the \gls{API}, interfaces and data storage
	\item[Network layer] connects all layers together.
		In many applications this may be implemented using conventional networking techniques such as WiFi or wire networks.
		However, recently, networks tailored to the needs of \gls{IOT} applications have been increasingly popular such as \gls{BLE}, LoRa, ZigBee or LTE-M.
	\item[Perception layer], also called edge layer, collects the data, interacts with the environment and consists of (edge) devices equipped with various sensors and actuators.
		As a special type of device, it may also contain a \gls{SN}.
		A \gls{SN} is a collection of sensors connected by a mesh network or central hub.
\end{description}

While the number of devices seems to be growing exponentially fast, programming \gls{IOT} systems remains difficult as there is a lot of semantic friction~\cite{ireland_classification_2009}.

The devices are a large heterogeneous collection of different platforms, protocols and languages resulting in impedance problems or semantic friction between layers~\cite{ireland_classification_2009}.

Additionaly, the perception layer often is a heterogeneous collections of microcontrollers as well, each having their own peculiarities, language of choice and hardware interfaces.
The hardware needs to be cheap, small-scale and energy efficient.
As a result, the \glspl{MCU} used to power these devices do not have a lot of computational power, a soup\c{c}on of memory, and little communication bandwidth.
Typically the devices do not run a full fledged \gls{OS} but a compiled firmware.
This firmware is often written in an imperative language that needs to be flashed to the program memory.
It is possible to dynamically send the program to the program memory using \gls{OTA} programming~\cite{baccelli_scripting_2018,baccelli_reprogramming_2018}.
Program memory typically is flash based and only lasts a couple of thousand writes before it wears out.
While devices are getting a bit faster, smaller, and cheaper, they keep these properties to an extent.
The properties of the device greatly reduce the flexibility for dynamic systems where tasks are created on the fly, executed on demand and require parallel execution.
These problems can be mitigated by dynamically sending code to be interpreted to the \gls{MCU}.
With interpretation, a specialized interpreter is flashed in the program memory once that receives the program code to execute at runtime.

%weiser_computer_1991
\section{Domain-specific languages}
% General
Programming languages can be divided up into two categories: \glspl{DSL} and \glspl{GPL}~\cite{fowler_domain_2010}.
Where \glspl{GPL} are not made with a demarcated area in mind, \glspl{DSL} are tailor-made for a specific domain.
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.
\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).

\begin{figure}[ht]
	\centering
	\includestandalone{hyponymy_of_dsls}
	\caption{Hyponymy of \glspl{DSL} (adapted from~\cite[pg.\ 2]{mernik_extensible_2013})}%
	\label{fig:hyponymy_of_dsls}
\end{figure}

\glspl{DSL} where historically created as standalone languages which means all the machinery is developed solely for the language.
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.
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.
Examples of standalone \glspl{DSL} are regular expressions, make, yacc, XML, SQL, \etc.

A radically different approach is embeddding the \gls{DSL} in a host language, i.e.\ \glspl{EDSL}~\cite{hudak_modular_1998}.
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.
There are however two sides to the this coin.
If the syntax of the host language is not very flexible, the syntax of the \gls{DSL} may become clumsy.
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}.

Tratt applied a notion from metaprogramming~\cite{sheard_accomplishments_2001} to \glspl{EDSL} to define homogeneity and heterogeneity of \glspl{EDSL} as follows~\cite{tratt_domain_2008}:
\begin{quote}
	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.
\end{quote}
Homogeneous \glspl{EDSL} are therefore languages that are solely defined as an extension to their host language.
They often restrict features of the host language to provide a safer interface or capture an idiomatic pattern in the host language for reuse.
The difference between a library and a homogeneous \glspl{EDSL} is not always clear.
Examples of homogeneous \glspl{EDSL} are libraries such as ones for \glspl{GUI} creation, LISP's macro system, \etc.

On the other hand, heterogeneous \glspl{EDSL} are languages that are not executed in the host language.
For example, Elliott et al.\ 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~\cite{elliott_compiling_2003}.
In fact, \gls{ITASK} and \gls{MTASK} are both heterogeneous \glspl{EDSL}.

\section{Task-oriented programming}
\Gls{TOP} is a declarative programming paradigm designed to model interactive systems~\cite{plasmeijer_task-oriented_2012}.
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.
From the data types, utilising various \emph{type-parametrised} concepts, all other aspects are handled (see \cref{fig:tosd}).
This approach to software development is also called \gls{TOSD}~\cite{wang_maintaining_2018}.

\begin{figure}[ht]
	\centering
	\begin{subfigure}[t]{.5\textwidth}
		\centering
		\includestandalone{traditional}
		\caption{Traditional layered approach.}
	\end{subfigure}%
	\begin{subfigure}[t]{.5\textwidth}
		\centering
		\includestandalone{tosd}
		\caption{\Gls{TOSD} approach.}
	\end{subfigure}
	\caption{Separation of concerns in a traditional setting and in \gls{TOSD} (adapted from~\cite[pg.\ 20]{wang_maintaining_2018}).}%
	\label{fig:tosd}
\end{figure}

\begin{description}
	\item[Presentation layer: UI]
		The \gls{UI} of the system is automatically generated from the representation of the type.
		For instance, \gls{TOP} languages implemented in an \gls{FP} language often use generic programming or template metaprogramming to automatically achieve this.
		\Gls{TOP} languages embedded in imperative programming languages may use introspection\todo{Do I want this sentence here?}.
		Even though the \gls{UI} is generated from the structure of the datatypes, in many practical \gls{TOP} systems it can be tweaked afterwards to suit the specific needs of the application.
	\item[Business layer: Tasks]
		A task is an abstract representation of a piece of work that needs to be done.
		It provides an intuitive abstraction over work in the real world.
		Just as with real-life tasks and workflow, tasks can be combined in various ways such as in parallel or in sequence.
		Furthermore, tasks are observable which means it is possible to observe a --- partial --- result during execution and act upon it by for example starting new tasks.
		Examples of tasks are filling in a form, sending an email, reading a sensor or even doing a physical task.
	\item[Resource access: \glspl{SDS}]
		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.
		Tasks can also share data using \glspl{SDS}.
		\Glspl{SDS} are an abstraction over any data.
		An \gls{SDS} can represent typed data stored in a file, a chunk of memory, a database \etc.
		\Glspl{SDS} can also represent external impure data such as the time, random numbers or sensory data.
		Similar to tasks, transformation and combination of \glspl{SDS} is possible.
	\item[\Gls{UOD}: PL]
		The \gls{UOD} from the business layer is explicitly and separately modelled by the relations that exist in the functions of the host language.
		\gls{TOP} languages are usually embedded in \gls{FP} languages but this not necessarily the case.
		Some host languages also provide the implementations for the tasks and \glspl{SDS}.
		\todo{dit moet beter}
\end{description}

\section{Outline}
\todo[inline]{uitbreiden}
%\epigraph{%
%	\textbf{rhapsody} /\textipa{['r\ae{}ps@di]}/ \emph{noun} (pl.\ \textbf{-ies}) a piece of music that is full of feeling and is not regular in form: Liszt's Hungarian Rhapsodies.
%}{%
%	Oxford Advanced Learners Dictionary~\cite{margaret_deuter_rhapsody_2015}.
%}
This thesis is structured as a purely functional rhapsody.
On Wikipedia, a rhapsody is defined as follows~\cite{wikipedia_contributors_rhapsody_2022}:
\begin{quote}
	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.
\end{quote}

This thesis follows the tradition and consists of three movements that are episodic yet integrated.
\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}.
The movements are readable independently if the reader is familiarised with the background material provided in \cref{chp:introduction}.
The thesis wraps up with \cref{chp:conclusion} that provides a conclusion and an outlook on future work.

\subsection{\Cref{prt:dsl}: Domain-specific languages}
This movement is a cumulative---paper-based---movement that focusses on techniques for embedding \glspl{DSL} in functional programming lanugages.
After reading the first chapter, subsequent chapters in this movement are readable as independently.

\subsubsection{\Cref{chp:dsl_embedding_techniques}}
This chapter shows the basic \gls{DSL} embedding techniques and compares the properties of several embedding methods.
This chapter is not based on a paper and written as a background for the subsequent chapters in the movement.

\subsubsection{\Cref{chp:classy_deep_embedding}} 
This chapter is based on the paper: \emph{Deep Embedding with Class}~\todo{cite when published}.

During a Master's thesis supervision~\cite{amazonas_cabral_de_andrade_developing_2018}, 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.
Slowly the ideas organically grew to form the technique shown in the paper.

The research from this paper and writing the paper was solely performed by me.

\subsubsection{\Cref{chp:first-class_datatypes}} shows how to inherit data types in \glspl{EDSL} using metaprogramming.
This chapter is based on the paper: \emph{First-Class Data Types in Shallow Embedded Domain-Specific Languages using Metaprogramming}~\todo{cite when accepted}.

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.
%
%\subsubsection{\Cref{chp:strongly-typed_multi-view_stack-based_computations}} shows how to use advanced \gls{DSL} techniques to embed type safe stack-based computations in a host language.
%This chapter is based on the paper: \emph{Strongly-Typed Multi-View Stack-Based Computations}~\todo{cite when accepted}.
%\todo{Zal ik dit paper wel opnemen? Aangezien Pieter het grotendeels gedaan heeft?}
%
%I supported Pieter Koopman in performing the research in this paper by writing some of the software.
%The paper was mostly written by Pieter Koopman\todo{probably will be}.

\subsection{\Cref{prt:top}: Task-oriented \texorpdfstring{\acrlong{IOT}}{internet of things} programming }
This part is a monograph focussing on \glspl{TOP} for the \gls{IOT}.
Therefore, the chapters depend on eachother and are best read in order.
The monograph is compiled from the following papers and revised lecture notes.

\begin{itemize}
	\item \bibentry{koopman_task-based_2018}.

		This was the initial \gls{TOP}/\gls{MTASK} paper.
		Pieter Koopman wrote it but I helped with the software and research.
	\item \bibentry{lubbers_task_2018}.
		
		This paper was an extension of my Master's thesis~\cite{lubbers_task_2017}.
		It shows how a simple imperative variant of \gls{MTASK} was integrated with \gls{ITASK}.
		While the language was a lot different than later versions, the integration mechanism is still used in \gls{MTASK} today.

		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.
	\item \bibentry{lubbers_multitasking_2019}.

		This paper was a short paper on the multitasking capabilities of \gls{MTASK} in contrast to traditional multitasking methods for \gls{ARDUINO}.
	\item \emph{Simulation of a Task-Based Embedded Domain Specific Language for the Internet of Things}~\todo{cite when published}

		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.

		Pieter Koopman wrote and taught it though I helped with the software and research.
	\item \emph{Writing Internet of Things applications with Task Oriented Programming}~\todo{cite when published}

		These revised lecture notes are from a course on programming in \gls{MTASK} provided at the 2019 CEFP/3COWS summer school in Budapest, Hungary.

		Pieter prepared half of the lecture. I wrote the lecture notes, prepared the other half of the lecture, the assignments and practical session.
	\item \bibentry{lubbers_interpreting_2019}.

		This paper showed an implementation for \gls{MTASK} for microcontrollers in the form of a compilation scheme and informal semantics description.

		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.
	\item \emph{Reducing the Power Consumption of IoT with Task-Oriented Programming}~\todo{cite when published}

		This paper shows how to create a scheduler so that devices running \gls{MTASK} tasks can go to sleep more automatically.
		Furthermore, it shows how to integrate hardware interrupts into \gls{MTASK}.
		The research was carried out by Sjoerd Crooijmans during his Master's thesis~\cite{crooijmans_reducing_2021}.
		I did the daily supervision and helped with the research, Pieter Koopman was the formal supervisor and wrote most of the paper.
	\item \emph{Asynchronous Shared Data Sources}~\todo{cite when accepted}

		\todo[inline]{This paper could in theory be dropped in favour of being done sooner with the thesis}

		Asynchronous \glspl{SDS} are used in the current \gls{ITASK} system and allow bigger \gls{IOT} devices such as raspberry pi's to be used in a tierless \gls{ITASK} system.
		The example application shown in \cref{prt:tvt} heavily uses asynchronous \glspl{SDS}.
		This paper shows how to lift \glspl{SDS} to operate asynchronously independent of \gls{ITASK} or another \gls{TOP} implementation.

		The initial research was carried out by Haye B\"ohm during his Master's thesis~\cite{bohm_asynchronous_2019}.
		I did the daily supervision and helped with the research, Pieter Koopman and Rinus Plasmeijer were the formal supervisors.
		I extended and generalised the research and wrote the paper.
	\item \emph{Green Computing for the Internet of Things}~\todo[inline]{cite when done}

		These revised lecture notes are from a course on sustainable programming using \gls{MTASK} provided at the 2022 Sustrainable summer school in Rijeka, Croatia.

		Pieter prepared half of the lecture and wrote the introduction.
		I wrote the middle part of the lecture notes, prepared the other half of the lecture, the assignments and the practical session.
\end{itemize}

The movement is made up out of the following chapters
\todo[inline]{preliminary}

\begin{itemize}
	\item The mTask language (includes informal semantics)
		\begin{itemize}
			\item Expressions
			\item Functions
			\item Tasks
			\item Shares
			\item Peripherals
		\end{itemize}
	\item Interpretations/views/backends\todo{decide on terminology}
	\item Green computing
	\item Integration with iTask
	\item Implementation (based on IFL19 paper)
	\item TOP for IoT beyond microprocessors
\end{itemize}

\subsection{\Cref{prt:tvt}: Tiered versus tierless programming}
These chapters focus on comparing traditional tiered architectures to tierless architectures and are based on a single journal paper that extended on a conference paper.
The conference paper was partly funded by the Radboud-Glasgow Collaboration Fund.
It does both a qualitative and a quantitative four-way comparison of a smart campus application.

The research in these papers and writing them was performed by all authors.
I created the server application, the \gls{CLEAN}/\gls{ITASK}/\gls{MTASK} implementation (\acrshort{CWS}) and the \gls{CLEAN}/\gls{ITASK} implementation (\acrshort{CRS})
Adrian Ramsingh created the micropython implementation (\acrshort{PWS}), the original python implementation (\acrshort{PRS}) and the server application were created by Jeremy Singer, Dejice Jacob and Kristian Hentschel~\cite{hentschel_supersensors:_2016}.

\begin{itemize}
	\item \bibentry{lubbers_tiered_2020}.
	\item \emph{Could Tierless Languages Reduce IoT Development Grief?}~\todo[inline]{cite when accepted}
\end{itemize}

\newcounter{secondauthorcnt}
\newcounter{underreviewcnt}
\newcounter{plannedcnt}
\newcounter{publicationscnt}
\newcommand{\secondauthor}{\textsuperscript{$\ast$}\stepcounter{secondauthorcnt}}
\newcommand{\underreview}{\textsuperscript{$\dagger$}\stepcounter{underreviewcnt}}
\newcommand{\planned}{\textsuperscript{$\ddagger$}\stepcounter{plannedcnt}}

\subsection{List of publications}
\begin{enumerate}
	\item \secondauthor{}
		A Task-Based DSL for Microcomputers

		P. Koopman\footnote{\orcid{0000-0002-3688-0957}}, M. Lubbers\footnote{\orcid{0000-0002-4015-4878}}, and R. Plasmeijer (RWDSL 2018)~\cite{koopman_task-based_2018}.
	\item Task Oriented Programming and the Internet of Things

		M. Lubbers, P. Koopman, and R. Plasmeijer (IFL 2018)~\cite{lubbers_task_2017} (extension of Master's thesis~\cite{lubbers_task_2018}).
	\item Multitasking on Microcontrollers using Task Oriented Programming

		M. Lubbers, P. Koopman, and R. Plasmeijer (MIPRO/4COWS 2019)~\cite{lubbers_multitasking_2019}.
	\item \secondauthor{}
		Simulation of a Task-Based Embedded Domain Specific Language for the Internet of Things

		P. Koopman, M. Lubbers, and R. Plasmeijer (CEFP/3COWS 2018).
	\item Writing Internet of Things applications with Task Oriented Programming

		M. Lubbers, P. Koopman, and R. Plasmeijer (CEFP/3COWS 2019).
	\item Interpreting Task Oriented Programs on Tiny Computers

		M. Lubbers, P. Koopman, and R. Plasmeijer (IFL 2019)~\cite{lubbers_interpreting_2019}.
	\item Tiered versus Tierless IoT Stacks: Comparing Smart Campus Software Architectures

		M. Lubbers, P. Koopman, A. Ramsingh\footnote{\orcid{0000-0003-3501-902X}}, J. Singer\footnote{\orcid{0000-0001-9462-6802}}, and P. Trinder\footnote{\orcid{0000-0003-0190-7010}} (IoT 2020)~\cite{lubbers_tiered_2020}.

	% in press
	\item Deep Embedding with Class

		M. Lubbers (TFP 2022).
	\item \secondauthor{}
		Reducing the Power Consumption of IoT with Task-Oriented Programming

		S. Crooijmans, M. Lubbers, and P. Koopman (TFP 2022).

	%Under review
	\item \underreview{} Could Tierless Languages Reduce IoT Development Grief?

		M. Lubbers, P. Koopman, A. Ramsingh, J. Singer, and P. Trinder (ACM TIOT) (extension of~\cite{lubbers_tiered_2020}).
	\item \secondauthor\underreview{}
		Strongly-Typed Multi-View Stack-Based Computations

		M. Lubbers and P. Koopman (IFL 2022 under review).
	\item \underreview{} First-Class Data Types in Shallow Embedded Domain-Specific Languages using Metaprogramming

		M. Lubbers, P. Koopman, and R. Plasmeijer (IFL 2022 under review).
	\item \underreview{} Asynchronous Shared Data Sources

		M. Lubbers, H. Böhm, P. Koopman, and R. Plasmeijer (IFL 2022 under review).

	%Planned
	\item \planned{} Green Computing for the Internet of Things

		M. Lubbers, P. Koopman (Sustrainable 2022 planned).

		\setcounter{publicationscnt}{\value{enumi}}
\end{enumerate}

There are \thepublicationscnt{} publications of which \thesecondauthorcnt{} I'm second author, \theunderreviewcnt{} are under review and \theplannedcnt{} are planned.

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