Microcontrollers are equipped with a lot of connectivity for integrating peripherals such as sensors and actuators.
The connectivity makes them very suitable to interact with their surroundings.
These miniature computers contain integrated circuits that accommodate a microprocessor designed for use in embedded applications.
-As a consequence, microcontrollers are cheap; tiny; have little memory; and contain a slow, but energy-efficient processor.
+As a consequence, microcontrollers are cheap, tiny, have little memory, and contain a slow, but energy-efficient processor.
When coordinating an orchestra of edge devices, there is room for little error.
Edge devices come and go, perform their own pieces, or are sometimes instructed to perform a certain piece, they might even operate without a central authority.
This results in semantic friction, which makes programming and maintaining \gls{IOT} systems a complex and error-prone process.
This dissertation describes the research carried out around orchestrating these complex \gls{IOT} systems using \gls{TOP}.
-\Gls{TOP} is an innovative tierless programming paradigm for interactive multi-layered systems.
+\Gls{TOP} is an innovative tierless programming paradigm for interactive multi-layered systems\todo{tierless introductie mist een beetje}.
By utilising advanced compiler technologies, much of the internals, communication, and interoperation between the tiers or layers of the applications are automatically generated.
-The compiler makes an application controlling all interconnected components from a single declarative specification of the required work.
+The compiler generates an application controlling all interconnected components from a single declarative specification of the required work.
For example, the \gls{TOP} system \gls{ITASK} is used to program all layers of multi-user distributed web applications from a single source specification.
It is implemented in the general-purpose lazy functional programming language \gls{CLEAN}, and therefore requires relatively powerful hardware.
The inflated hardware requirements are no problem for regular computers but impractical for the average edge device.
This is where an additional \glspl{DSL} must play its part.
\Glspl{DSL} are programming languages tailored to a specific domain.
-Consequently, jargon is not expressed in terms of the language itself, but are built-in language features.
+Consequently, jargon is not expressed in terms of the language itself, but is built into the language.
Furthermore, the \gls{DSL} can eschew language or system features that are irrelevant for the domain.
Using \glspl{DSL}, hardware requirements can be drastically lowered, even while maintaining a high abstraction level for the specified domain.
\section{Reading guide}%
\label{lst:reading_guide}
This work is structured as a purely functional rhapsody.
-The \citet{wikipedia_contributors_rhapsody_2022} define a musical rhapsody is defined as follows:
+The \citet{wikipedia_contributors_rhapsody_2022} define a musical rhapsody as follows:
\begin{quote}\emph{%
A \emph{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.}
\end{quote}
\emph{The \glsxtrlong{IOT}, or \glsxtrshort{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}
-Much later, CISCO states that the \gls{IOT} started when there were as many connected devices as there were people on the globe, i.e.\ around 2008 \citep{evans_internet_2011}.
+Much later, CISCO stated that the \gls{IOT} started when there were as many connected devices as there were people on the globe, i.e.\ around 2008 \citep{evans_internet_2011}.
Today, \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 they operate in.
These connected devices are already in households all around us in the form of smart electricity meters, fridges, phones, watches, home automation, \etc.
In some applications this is implemented using conventional networking techniques such as \gls{WIFI} or Ethernet.
However, network technology that is tailored to the needs of the specific interconnection between two layers is increasingly popular.
Examples of this are BLE, LoRa, ZigBee, and LTE-M as a communication protocol for connecting the perception layer to the application layer using \gls{IOT} transport protocols such as \gls{MQTT}.
-Protocols such as HTTP, AJAX, and WebSocket connecting the presentation layer to the application layer that are designed for the use in web applications.
+Furthermore, protocols such as HTTP, AJAX, and WebSocket are designed for the use in web applications and connect the presentation layer to the application layer.
Across the layers, the devices are a large heterogeneous collection of different platforms, protocols, paradigms, and programming languages.
As a result, impedance problems or semantic friction occurs between layers and the maintainability is severely hampered \citep{ireland_classification_2009}.
-Even more so, the perception layer itself is often a heterogeneous collection of microcontrollers in itself, each having their own peculiarities, programming language of choice, and hardware interfaces.
+Even more so, the perception layer often is a heterogeneous collection of microcontrollers in itself, each having their own peculiarities, programming language of choice, and hardware interfaces.
As edge hardware needs to be cheap, small scale, and energy efficient, the microcontrollers used to power them do not have a lot of computational power, only a smidge of memory, and little communication bandwidth.
Typically, these devices are unable to run a full-fledged general-purpose \gls{OS}.
Rather they employ compiled firmware written in imperative languages that combines all tasks on the device in a single program.
\section{Domain-specific languages}%
\label{sec:back_dsl}
% General
-Programming languages can be divided up into two categories: \glspl{DSL} and \glspl{GPL} \citep{fowler_domain_2010}.
+Programming languages can be divided into two categories: \glspl{DSL} and \glspl{GPL} \citep{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 a \gls{DSL} is easier and requires less \gls{GPL} knowledge for a domain expert.
This does come at the cost of the \gls{DSL} being sometimes less expressive to an extent that it may not even be Turing complete.
For example, \citet{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.
Both \gls{ITASK} and \gls{MTASK} are \glspl{EDSL}.
-Programs written in \gls{ITASK} run in the host language, and it is a homogeneous \gls{DSL}.
+Programs written in \gls{ITASK} run in the host language, and hence \gls{ITASK} is a homogeneous \gls{DSL}.
Tasks written using \gls{MTASK} are dynamically compiled to byte code for an edge device, making it a heterogeneous \gls{DSL}.
The interpreter running on the edge device has no knowledge of the higher level task specification.
It just interprets the byte code it was sent and takes care of the communication.
\subsection{The iTask system}
The concept of \gls{TOP} originated from the \gls{ITASK} framework, a declarative \gls{TOP} language for defining interactive distributed web applications.
The \gls{ITASK} system is implemented as an \gls{EDSL} in the programming language \gls{CLEAN} \citep{plasmeijer_itasks:_2007,plasmeijer_task-oriented_2012}\footnote{\Cref{chp:clean_for_haskell_programmers} contains a guide for \gls{CLEAN} tailored to \gls{HASKELL} programmers.}.
-It is under development for over fifteen years and has proven itself through use in industry as well.
+It has been under development for over fifteen years and has proven itself through use in industry.
For example, it is the main language of VIIA, an advanced application for monitoring coasts \citep{top_software_viia_2023}.
Browsers are powering \gls{ITASK}'s presentation layer.
The browser runs the actual \gls{ITASK} code using an interpreter that operates on \gls{CLEAN}'s intermediate language \gls{ABC} \citep{staps_lazy_2019}.
\subsection{The mTask system}
The work for \gls{IOT} edge devices can often be succinctly described by \gls{TOP} programs.
-Software on microcontrollers is usually composed of smaller basic tasks, are interactive, and share data with other components or the server.
+Software on microcontrollers is usually composed of smaller basic tasks, are interactive, and shares data with other components or the server.
The \gls{ITASK} system seems an obvious candidate for bringing \gls{TOP} to \gls{IOT} edge devices.
However, an \gls{ITASK} application contains many features that are not needed on \emph{edge devices} such as higher-order tasks, support for a distributed architecture, a multi-user web server, and facilities to generate \glspl{GUI} for any user-defined type.
Furthermore, \gls{IOT} edge devices are in general not powerful enough to run or interpret \gls{CLEAN}\slash\gls{ABC} code, they just lack the processor speed and memory.
The \gls{MTASK} language is written in \gls{CLEAN} as a multi-view \gls{EDSL} and hence there are multiple interpretations possible.
This thesis mostly discusses the byte code compiler.
From an \gls{MTASK} task constructed at run time, a compact binary representation of the work that needs to be done is compiled.
-And while the byte code for \gls{MTASK} is generated at run time, the type system of the host language \gls{CLEAN} prevents type errors in the generated code.
+While the byte code for \gls{MTASK} is generated at run time, the type system of the host language \gls{CLEAN} prevents type errors in the generated code.
This byte code is then sent to a device that running the \gls{MTASK} \gls{RTS}.
This feather-light domain-specific \gls{OS} is written in portable \gls{C} with a minimal device specific interface and it executes the tasks using interpretation and rewriting.
To illustrate \imtask{}, an example application is shown.
-The application is an interactive application for blinking \pgls{LED} on the microcontroller at a certain frequency that can be set and updated at run time.
+It is an interactive program for blinking \pgls{LED} on the microcontroller at a certain frequency that can be set and updated at run time.
\Cref{lst:intro_blink,fig:intro_blink} show the \gls{ITASK} part of the code and a screenshot.
Using \cleaninline{enterInformation}, the connection specification of the \gls{TCP} device is queried through a web editor (\cref{lst:intro_enterDevice,fig:intro_blink_dev}).
\Cref{lst:intro_withshared} defines \pgls{SDS} to communicate the blinking interval between the server and the edge device.
\subsection{Other TOP languages}
While \gls{ITASK} conceived \gls{TOP}, it is no longer the only \gls{TOP} system.
-Some \gls{TOP} languages were created to fill a gap encountered in practise.
+Some \gls{TOP} languages were created to fill a gap encountered in practice.
Toppyt \citep{lijnse_toppyt_2022} is a general purpose \gls{TOP} language written in \gls{PYTHON} used to host frameworks for modelling command \& control systems.
The hTask system is a \gls{TOP} system written in \gls{HASKELL} used as a vessel for experimenting with asynchronous \glspl{SDS} \citep{lubbers_htask_2022}.
Furthermore, some \gls{TOP} systems arose from Master's and Bachelor's thesis projects.
This section provides a thorough overview of the relation between the scientific publications and the contents of this thesis.
\subsection{\Fullref{prt:dsl}}
-The \gls{MTASK} system is an \gls{EDSL} and during the development of it, several novel basal techniques for embedding \glspl{DSL} in \gls{FP} languages have been found.
-This paper-based episode contains the following papers:
+The \gls{MTASK} system is an \gls{EDSL} and during the development of it, several novel basal techniques for embedding \glspl{DSL} in \gls{FP} languages were found.
+This paper-based episode is based on the following papers:
\begin{enumerate}
\item \emph{Deep Embedding with Class} \citep*{lubbers_deep_2022} is the basis for \cref{chp:classy_deep_embedding}.
It shows a novel deep embedding technique for \glspl{DSL} where the resulting language is extendible both in constructs and in interpretation just using type classes and existential data types.
repositories / phd-thesis.git / blobdiff