arch.example.tex

   1 \subsection{Framework}
   2 Systems built with support for \gls{mTask} are often following the same design
   3 pattern. First the devices are created --- with or without the interaction of
   4 the user --- and they are then connected. When all devices are registered, the
   5 \gls{mTask}-\glspl{Task} can be sent and \gls{iTasks}-\glspl{Task} can be
   6 started to monitor the output. When everything is finished, the devices are
   7 removed and the system is powered off.
   8
   9 \begin{lstlisting}[language=Clean,label={lst:framework},
  10         caption={\gls{mTask} framework for building applications}]
  11 w :: Task ()
  12 w =         makeDevice "dev1" (...) >>= connectDevice
  13         >>= \dev1->makeDevice "dev2" (...) >>= connectDevice
  14         >>= \dev2->...
  15         ...
  16         >>* [OnAction (Action "Shutdown") $ always
  17                 $   deleteDevice dev1
  18                 >>| deleteDevice dev2
  19                 >>| ...
  20                 >>| shutDown 0
  21         ]
  22 \end{lstlisting}
  23
  24 \subsection{Thermostat}
  25 The thermostat is a classic example program for showing interactions between
  26 peripherals. The following program shows a system containing two devices. One
  27 device is connected via \gls{TCP} and contains a temperature sensor. The second
  28
  29 \subsection[Lifting mTasks to iTasks-Tasks]%
  30         {Lifting \gls{mTask}-\glspl{Task} to \gls{iTasks}-\glspl{Task}}
  31 If the user does not want to know where and when a \gls{mTask} is actually
  32 executed and is just interested in the results it can lift the \gls{mTask} to
  33 an \gls{iTasks}-\gls{Task}. The function is called with a name, \gls{mTask},
  34 device and interval specification and it will return a \gls{Task} that finishes
  35 if and only if the \gls{mTask} has returned.
  36
  37 \begin{lstlisting}[caption={Starting up the devices}]
  38 liftmTask :: String (Main (ByteCode () Stmt)) (MTaskDevice, MTaskInterval) -> Task [MTaskShare]
  39 liftmTask wta mTask c=:(dev, _)= sendTaskToDevice wta mTask c
  40         >>= \(t, shs)->wait "Waiting for mTask to return" (taskRemoved t) (deviceShare dev)
  41         >>| viewInformation "Done!" [] ()
  42         >>| treturn shs
  43 where
  44         taskRemoved t d = isNothing $ find (\t1->t1.ident==t.ident) d.deviceTasks
  45 \end{lstlisting}
  46
  47 The factorial example can then be lifted to a real \gls{iTasks}-\gls{mTask}
  48 with the following code:
  49 \begin{lstlisting}[caption={Lifting the factorial \gls{Task} to \gls{iTasks}}]
  50 factorial :: MTaskDevice -> Task BCValue
  51 factorial dev = enterInformation "Factorial of ?" []
  52         >>= \fac->liftmTask "fact" (fact fac) (dev, OnInterval 100)
  53         @         fromJust o find (\x->x.humanName == "result")
  54         @         \s->s.MTaskShare.value
  55 where
  56         fact i = sds \y=i
  57                 In namedsds \x=(1 Named "result")
  58                 In {main = IF (y <=. lit 1)
  59                         ( pub x :. retrn                  )
  60                         ( x =. x *. y :.  y =. y -. lit 1 )}
  61 \end{lstlisting}