\section{iTasks}
\gls{TOP} is a modern recent programming paradigm implemented as
-\gls{iTasks}\cite{achten_introduction_2015} in the pure lazy functional
-language \gls{Clean}\cite{brus_cleanlanguage_1987}. \gls{iTasks} is a
+\gls{iTasks}~\cite{achten_introduction_2015} in the pure lazy functional
+language \gls{Clean}~\cite{brus_cleanlanguage_1987}. \gls{iTasks} is a
\gls{EDSL} to model workflow tasks in the broadest sense. A \gls{Task} is just
a function that --- given some state --- returns the observable \CI{TaskValue}. The
\CI{TaskValue} of a \CI{Task} can have different states. Not all state
\caption{The states of a \CI{TaskValue}}\label{fig:taskvalue}
\end{figure}
-\begin{lstlisting}[language=Clean,label={lst:taskex},%
+\begin{lstlisting}[label={lst:taskex},%
caption={An example \gls{Task} for entering a name}]
:: Name = { firstname :: String
, lastname :: String
Combinators describe relations between \glspl{Task}. \Glspl{Task} can be
combined in parallel, sequenced and their result values can be converted to
\glspl{SDS}. Moreover, a very important combinator is the step combinator which
-starts a new task according to specified predicates on the \CI{TaskValue}.
-Type signatures of the basic combinators are shown in
+starts a new \gls{Task} according to specified predicates on the
+\CI{TaskValue}. Type signatures of the basic combinators are shown in
Listing~\ref{lst:combinators}.
\begin{itemize}
dictates.
\end{itemize}
-\begin{lstlisting}[language=Clean,%
+\begin{lstlisting}[%
caption={\Gls{Task}-combinators},label={lst:combinators}]
//Step combinator
(>>*) infixl 1 :: (Task a) [TaskCont a (Task b)] -> Task b | iTask a & iTask b
(-&&-) infixr 4 :: (Task a) (Task b) -> Task (a,b) | iTask a & iTask b
\end{lstlisting}
-\section{\acrlongpl{SDS}}
+\section{Shared Data Sources}
\Glspl{SDS} are an abstraction over resources that are available in the world
-or in the \gls{iTasks} system. The shared data can be a file on disk, it can be
-the time, a random integer or just some data stored in memory. The actual
+or in the \gls{iTasks} system. The shared data can be a file on disk, the
+system time, a random integer or just some data stored in memory. The actual
\gls{SDS} is just a record containing functions on how to read and write the
-source. In these functions the \CI{*World} is available and therefore it can
-interact with the outside world. The \CI{*IWorld} is also available and
-therefore the functions can also access other shares, possibly combining them.
+source. In these functions the \CI{*IWorld} --- which in turn contains the real
+program \CI{*World} --- is available. Accessing the outside world is required
+for interacting with it and thus the functions can access files on disk, raw
+memory, other \glspl{SDS} and hardware.
The basic operations for \glspl{SDS} are get, set and update. The signatures
-for these functions are shown in Listing~\ref{lst:shares}. All of the
-operations are atomic in the sense that during reading no other tasks are
-executed.
+for these functions are shown in Listing~\ref{lst:shares}. By default, all
+\glspl{SDS} are files containing a \gls{JSON} encoded version of the object and
+thus are persistent between restarts of the program. Library functions for
+shares residing in memory are available as well. The three main operations on
+shares are atomic in the sense that during reading no other \glspl{Task} are
+executed. The system provides useful functions to transform, map and combine
+\glspl{SDS} using combinators. The system also provides functionality to
+inspect the value of a \gls{SDS} and act upon a change. \Glspl{Task} waiting on
+a \gls{SDS} to change are notified when needed. This results in low resource
+usage because \glspl{Task} are never constantly inspecting \gls{SDS} values but
+are notified.
\begin{lstlisting}[%
- language=Clean,label={lst:shares},caption={\Gls{SDS} functions}]
+ label={lst:shares},caption={\Gls{SDS} functions}]
+:: RWShared p r w = ...
+:: ReadWriteShared r w :== RWShared () r w
+:: ROShared p r :== RWShared p () r
+:: ReadOnlyShared r :== ROShared () r
+
+:: Shared r :== ReadWriteShared r r
+
get :: (ReadWriteShared r w) -> Task r | iTask r
set :: w (ReadWriteShared r w) -> Task w | iTask w
upd :: (r -> w) (ReadWriteShared r w) -> Task w | iTask r & iTask w
+sharedStore :: String a -> Shared a | JSONEncode{|*|}, JSONDecode{|*|}
+\end{lstlisting}
+
+\section{Parametric Lenses}
+\Glspl{SDS} can contain complex data structures such as lists, trees and even
+resources in the outside world. Sometimes, an update action only updates a part
+of the resource. When this happens, all waiting \glspl{Task} looking at the
+resource are notified of the update. However, it may be the case that
+\glspl{Task} were only looking at parts of the structure that was not updated.
+To solve this problem, parametric lenses were
+introduced~\cite{domoszlai_parametric_2014}.
+
+Parametric lenses add a type variable to the \gls{SDS} that is in the current
+library functions fixed to the void type (i.e. \CI{()}). When a \gls{SDS}
+executes a write operation, it also provides the system with a notification
+predicate. This notification predicate is a function \CI{p -> Bool} where
+\CI{p} is the parametric lens type. This allows programmers to create a big
+\gls{SDS}, and have \glspl{Task} only look at parts of the big \gls{SDS}. This
+technique is used in the current system in memory shares. The \CI{IWorld}
+contains a map that is accessible through a \gls{SDS}. While all data is
+stored in the map, only \glspl{Task} looking at a specific entry are notified
+when the structure is updated. The type of the parametric lens is the key in
+the map.
+
+Functionality for setting parameters is added in the system. The most important
+functions are the \CI{sdsFocus} and the \CI{sdsLens} function. These functions
+are listed in Listing~\ref{lst:focus}. \CI{sdsFocus} allows the programmer to
+fix a parametric lens value. \CI{sdsLens} is a kind of \CI{mapReadWrite}
+including access to the parametric lens value. This allows the creation of
+for example \glspl{SDS} that only read and write to parts of the original
+\gls{SDS}.
+
+\begin{lstlisting}[label={lst:focus},
+ caption={Parametric lens functions}]
+sdsFocus :: p (RWShared p r w) -> RWShared p` r w | iTask p
+
+:: SDSNotifyPred p :== p -> Bool
+
+:: SDSLensRead p r rs = SDSRead (p -> rs -> MaybeError TaskException r)
+ | SDSReadConst (p -> r)
+:: SDSLensWrite p w rs ws = SDSWrite (p -> rs -> w -> MaybeError TaskException (Maybe ws))
+ | SDSWriteConst (p -> w -> MaybeError TaskException (Maybe ws))
+:: SDSLensNotify p w rs = SDSNotify (p -> rs -> w -> SDSNotifyPred p)
+ | SDSNotifyConst (p -> w -> SDSNotifyPred p)
+
+sdsLens :: String (p -> ps) (SDSLensRead p r rs) (SDSLensWrite p w rs ws) (SDSLensNotify p w rs)
+ (RWShared ps rs ws) -> RWShared p r w | iTask ps
\end{lstlisting}
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