\section{iTasks}
-\gls{TOP} is a modern recent programming paradigm implemented as
+\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 a
+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 \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}
- \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
+\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
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