+\section{Future work}
+There are many ways of extending the research on the \gls{MTASK} system that also concerns \gls{TOP} for resource constrained devices in general.
+Some obvious routes is to add features, support more platforms,
+
+\subsection{Security}
+\Gls{IOT} has reached the news many times regarding security and it is a big concern \citep{alhirabi_security_2021}.
+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.
+The security of \gls{MTASK} and the used protocols are deliberately overlooked at the moment
+The \gls{MTASK} language and \gls{RTS} are modular.
+For example, the communication channels are communication method agnostic and operate through a simple duplex channel interface.
+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.
+\Citet{de_boer_secure_2020} did preliminary research on securing the communication channels, which proved to be possible without many changes in the protocol.
+Nonetheless, this deserves much more attention.
+The future and related work for the security of \gls{MTASK} and tierless systems is more thoroughly presented in \cref{ssec_t4t:security}.
+
+\subsection{Advanced edge devices techniques}
+Edge devices may produce a lot of data and it is not always effective to send this data to the server for processing.
+Leaving the produced data and computations on the edge device is called \emph{edge computing} \citep{shi_edge_2016}.
+The \gls{MTASK} exhibits many properties of edge computing because it is possible to run entire workflows on the device.
+However, it is interesting to see how far this can be extended.
+The \gls{MTASK} language is a high-level \gls{DSL}, so it is obvious to introduce abstractions for edge computations.
+For example, add \gls{TOP} support for machine learning on the edge device using TinyML \citep{sanchez-iborra_tinyml-enabled_2020}.
+
+Another recent advance in \gls{IOT} programming is battery-less or even battery-free computing.
+Instead of equipping the edge device with a battery, a capacitor is used in conjunction with some energy harvesting systems such as a solar panel.
+With the use of intermittent computing, resuming the computation after a, possibly unexpected, power loss, operation can still be achieved \citep{hester_batteries_2019}.
+After a reset, the program state is resumed from a checkpoint that was stored in some non-volatile memory.
+Many intermittent computing solutions rely on annotations from the programmer to divide the program into atomic blocks, sometimes called \emph{tasks} as well.
+These blocks are marked as such because in the case of an reset of the system, the work must be done again.
+Examples of such blocks are \gls{I2C} transmissions or calculations that rely on recent sensor data.
+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.
+Furthermore, creating checkpoints should be 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.
+It is interesting to see what \gls{TOP} abstraction could be useful for intermittent computing and what solutions are required to make this work.
+
+Mesh networks allow for communication not only to-and-fro the device and server but also between devices.
+The \gls{ITASK} system already contains primitives for distributed operation.
+For example, it is possible to run tasks or share data with \glspl{SDS} on a different machine.
+It is interesting to investigate how this networking technique can be utilised in \gls{MTASK}.
+
+Finally, \glspl{FPGA} have been becoming cheaper and faster recently, allowing for purely functional code to be translated to \glspl{FPGA} code efficiently \citep{baaij_digital_2015}.
+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.
+
+\subsection{Formal semantics}
+Semantics allow reasoning about the language and programs in order do (symbolic) simulation, termination checking, task equivalence, or otherwise.
+For \gls{ITASK} there have been two attempts to formally specify the language.
+First \citet{koopman_executable_2011} defined a semantics used for property based testing based on a minimal version of \gls{ITASK}.
+Then \citet{plasmeijer_task-oriented_2012} formalised \gls{ITASK} by providing an executable semantics for the language.
+Both semantics are not suitable for formal reasoning due to the complexity.
+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}.
+\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}.
+Future research into extending the formal semantics of \gls{MTASK} is useful to give more guarantees on \gls{MTASK} programs.
+
+\subsection{\texorpdfstring{\Glsxtrlong{TOP}}{Task-oriented programming}}
+In order to keep the resource constraints low, the \gls{MTASK} language contains only a minimal set of simple task combinators.
+From these simple combinators, complex collaboration patterns can be described.
+The \gls{ITASK} language is designed exactly the opposite.
+From just a few super combinators, all other combinators are derived.
+However, this approach requires a very powerful host language in which task combinators can be defined in terms of the host language.
+It could be fruitful to investigate which workflows cannot be specified with the limited set of combinators available in \gls{MTASK}.
+Furthermore, it is unclear whether all derived combinators from \gls{ITASK} can be expressed in terms of \gls{MTASK} combinators.
+\Citet{van_der_aalst_workflow_2003} defines a benchmark set of workflow patterns.
+It is interesting to see which patterns can be implemented with \gls{MTASK}, and what additional combinators are needed.
+Moreover, editors are a crucial part of \gls{TOP}.
+In \gls{MTASK}, sensors can be seen as read-only shared editors that are updated by the system.
+It is interesting to investigate how actual interactive editors would fit in \gls{MTASK}.
+For example, many smartwatches contain touch sensitive screens that could be used to interact with the user in this way.
+Alternatively, sufficiently powerful edge devices can probably run simple web interfaces as well.
+
+\Glspl{SDS} in \gls{ITASK} have a rich set of combinators to transform and combine the \glspl{SDS} into new \gls{SDS}.
+In \gls{MTASK}, \glspl{SDS} are typed global variables that may or may not proxy an \gls{ITASK} \gls{SDS}.
+It could be interesting to port the \gls{SDS} combinators to \gls{MTASK} as well, allowing them to be transformed and combined also.
+
+\subsection{Usability}
+The promise of \glspl{DSL} has often been that a domain expert could program with little technical knowledge of the host programming language.
+Some even propose that a \gls{DSL} is a \gls{UI} for domain experts to computation platforms \citep{management_association_evaluating_2014}.
+In practise this is not always the case due to crippling syntax and convoluted error messages.
+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}.
+If the editor produces correct \gls{MTASK} code by construction, much of the problems could be avoided.
+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.
+Much research has gone into simplifying these error messages by translating them to the \gls{DSL} domain, see for example \citep{serrano_type_2018}.
+De Roos briefly investigated these methods in their research internship.
+A future directions could be to extend these findings and apply more \gls{EDSL} error message techniques on \gls{MTASK} as well.
+
+The serialisation and deserialisation of data types is automated both on the server and the \gls{MTASK} device using generic programming.
+Using the structural information of the data type, the code responsible for the functionality is automatically generated.
+Peripherals are not yet fully integrated in such a way.
+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.
+It would be interesting to investigate whether this can be automated or centralised in a way.
+
+More elaborate features in the type systems of modern functional programming languages allow for more type safety.
+The \gls{MTASK} language relies a lot on these features such as (multi-parameter) type classes and existential data types with class constraints.
+However, it should be possible to make abstractions over more stuff to make it safer.
+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.
+
+\subsection{Scheduling}
+The scheduling in \gls{MTASK} works quite well but it is not real time.
+There is a variant of \gls{FRP} called \gls{PFRP} that allows for real-time operation \citep{belwal_variable_2013}.
+Furthermore, an alternative to reducing the energy consumption by going to sleep is stepping down the processor frequency.
+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.
+\Citet{belwal_variable_2013} use \gls{PFRP} with \gls{DVFS} to reduce the energy consumption.
+It is interesting to investigate the possibilities for \gls{DVFS} in \gls{MTASK} and \gls{TOP} in general.
+