\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{TOP} is a novel 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 an
\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
+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
transitions are possible as shown in Figure~\ref{fig:taskvalue}. Once a value
-is stable it can never become unstable again. Stability is often reached
-by pressing a confirmation button. \glspl{Task} yielding a constant value are
+is stable it can never become unstable again. Stability is often reached by
+pressing a confirmation button. \glspl{Task} yielding a constant value are
immediately stable.
A simple \gls{iTasks} example illustrating the route to stability of a
For a type to be suitable, it must have instances for a collection of generic
functions that is captured in the class \CI{iTask}. Basic types have
-specialization instances for these functions and show an according interface.
-Generated interfaces can be modified with decoration operators.
+specialization instances for these functions and show an interface accordingly.
+Derived interfaces can be modified with decoration operators or specializations
+can be created.
\section{Combinators}
\Glspl{Task} can be combined using so called \gls{Task}-combinators.
-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
-Listing~\ref{lst:combinators}.
-
-\begin{itemize}
- \item Step:
-
- The step combinator is used to start \glspl{Task} when a predicate on
- the \CI{TaskValue} holds or an action has taken place. The bind
- operator can be written as a step combinator.
- \begin{lstlisting}[language=Clean]
-(>>=) infixl 1 :: (Task a) (a -> (Task b)) -> (Task b) | iTask a & iTask b
-(>>=) ta f = ta >>* [OnAction "Continue" onValue, OnValue onStable]
- where
- onValue (Value a _) = Just (f a)
- onValue _ = Nothing
-
- onStable (Value a True) = Just (f a)
- onStable _ = Nothing
- \end{lstlisting}
- \item Parallel:
-
- The parallel combinator allows for concurrent \glspl{Task}. The
- \glspl{Task} combined with these operators will appear at the same time
- in the web browser of the user and the results are combined as the type
- dictates.
-\end{itemize}
+Combinators describe relations between \glspl{Task}. There are only two basic
+types of combinators; namely parallel and sequence. All other combinators are
+derived from the basic combinators. Type signatures of simplified versions of
+the basic combinators and their derivations are given in
+Listing~\ref{lst:combinators}
\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
(>>=) infixl 1 :: (Task a) (a -> Task b) -> Task b | iTask a & iTask b
+(>>*) infixl 1 :: (Task a) [TaskCont a (Task b)] -> Task b | iTask a & iTask b
:: TaskCont a b
= OnValue ((TaskValue a) -> Maybe b)
| OnAction Action ((TaskValue a) -> Maybe b)
(-&&-) infixr 4 :: (Task a) (Task b) -> Task (a,b) | iTask a & iTask b
\end{lstlisting}
+\paragraph{Sequence:}
+The implementation for the sequence combinator is called the
+\CI{step} (\CI{>>*}). This combinator runs the left-hand \gls{Task} and
+starts the right-hand side when a certain predicate holds. Predicates
+can be propositions about the \CI{TaskValue}, user actions from within
+the web browser or a thrown exception. The familiar
+bind-combinator is an example of a sequence combinator. This combinator
+runs the left-hand side and continues to the right-hand \gls{Task} if
+there is an \CI{UnStable} value and the user presses continue or when
+the value is \CI{Stable}. The combinator could have been implemented
+as follows:
+\begin{lstlisting}[language=Clean]
+(>>=) infixl 1 :: (Task a) (a -> (Task b)) -> (Task b) | iTask a & iTask b
+(>>=) ta f = ta >>* [OnAction "Continue" onValue, OnValue onStable]
+ where
+ onValue (Value a _) = Just (f a)
+ onValue _ = Nothing
+
+ onStable (Value a True) = Just (f a)
+ onStable _ = Nothing
+\end{lstlisting}
+
+\paragraph{Parallel:}
+The parallel combinator allows for concurrent \glspl{Task}. The
+\glspl{Task} combined with these operators will appear at the same time
+in the web browser of the user and the results are combined as the type
+dictates. All parallel combinators used are derived from the basic parallel
+combinator that is very complex and only used internally.
+
\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, 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{*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 shares and hardware.
+\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}. By default, all
-shares 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 tasks 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.
+\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}[%
label={lst:shares},caption={\Gls{SDS} functions}]
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
-share, and have \glspl{Task} only look at parts of the big share. This
+\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 an \gls{SDS}. While all data is
+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
-function is the \CI{sdsFocus} function. This function is listed in
-Listing~\ref{lst:focus} and allows the programmer to fix the parametric lens to
-a specific value.
+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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