top.itasks.tex

   1 \gls{TOP} is a novel programming paradigm implemented as
   2 \gls{iTasks}~\cite{achten_introduction_2015} in the pure lazy functional
   3 language \gls{Clean}~\cite{brus_cleanlanguage_1987}. \gls{iTasks} is an
   4 \gls{EDSL} to model workflow tasks in the broadest sense. A \gls{Task} is just
   5 a function that --- given some state --- returns the observable \CI{TaskValue}.
   6 The \CI{TaskValue} of a \CI{Task} can have different states. Not all state
   7 transitions are possible as shown in Figure~\ref{fig:taskvalue}. Once a value
   8 is stable it can never become unstable again. Stability is often reached by
   9 pressing a confirmation button. \glspl{Task} yielding a constant value are
  10 immediately stable.
  11
  12 A simple \gls{iTasks} example illustrating the route to stability of a
  13 \gls{Task} in which the user has to enter a full name is shown in
  14 Listing~\ref{lst:taskex}. The code is accompanied by screenshots showing the
  15 user interface in Figure~\ref{fig:taskex1},~\ref{fig:taskex2}
  16 and~\ref{fig:taskex3}. The \CI{TaskValue} of the \gls{Task} is in the first
  17 image in the \CI{NoValue} state, the second image does not have all the fields
  18 filled in and therefore the \CI{TaskValue} remains \CI{NoValue}. In the third
  19 image all fields are entered and the \CI{TaskValue} transitions to the
  20 \CI{Unstable} state. When the user presses \emph{Continue} the value becomes
  21 \CI{Stable} and cannot be changed any further.
  22
  23 \begin{figure}[H]
  24         \centering
  25         \includegraphics[width=.5\linewidth]{fig-taskvalue}
  26         \caption{The states of a \CI{TaskValue}}\label{fig:taskvalue}
  27 \end{figure}
  28
  29 \begin{lstlisting}[language=Clean,label={lst:taskex},%
  30         caption={An example \gls{Task} for entering a name}]
  31 :: Name = { firstname :: String
  32           , lastname  :: String
  33           }
  34
  35 derive class iTask Name
  36
  37 enterInformation :: String [EnterOption m] -> (Task m) | iTask m
  38
  39 enterName :: Task Name
  40 enterName = enterInformation "Enter your name" []
  41 \end{lstlisting}
  42
  43 \begin{figure}[H]
  44         \centering
  45         \begin{subfigure}{.25\textwidth}
  46                 \centering
  47                 \includegraphics[width=.9\linewidth]{taskex1}
  48                 \caption{Initial interface}\label{fig:taskex1}
  49         \end{subfigure}
  50         \begin{subfigure}{.25\textwidth}
  51                 \centering
  52                 \includegraphics[width=.9\linewidth]{taskex2}
  53                 \caption{Incomplete entrance}\label{fig:taskex2}
  54         \end{subfigure}
  55         \begin{subfigure}{.25\textwidth}
  56                 \centering
  57                 \includegraphics[width=.9\linewidth]{taskex3}
  58                 \caption{Complete entry}\label{fig:taskex3}
  59         \end{subfigure}
  60         \caption{Example of a generated user interface}
  61 \end{figure}
  62
  63 For a type to be suitable, it must have instances for a collection of generic
  64 functions that is captured in the class \CI{iTask}. Basic types have
  65 specialization instances for these functions and show an interface accordingly.
  66 Derived interfaces can be modified with decoration operators or specializations
  67 can be created.
  68