methods.mtask.tex

   1 \section{mTask}
   2 The \gls{mTask}-\gls{EDSL} is the basis on which the system is built. The
   3 \gls{mTask} was created by Koopman et al.\ to support several views such as an
   4 \gls{iTasks} simulation and a \gls{C}-code generator. The \gls{EDSL} was
   5 designed to generate a ready to compile \gls{TOP}-like system for
   6 microcontrollers such as the Arduino\cite{koopman_type-safe_nodate}%
   7 \cite{plasmeijer_shallow_2016}.
   8
   9 The \gls{mTask}-\gls{EDSL} is a shallowly embedded class based \gls{EDSL} and
  10 therefore it is very suitable to have a new backend that partly implements the
  11 given classes. The following subsections show the details of the \gls{EDSL}
  12 that are used in the extension. The parts of the \gls{EDSL} that are not used
  13 will not be discussed and the details of those parts can be found in the cited
  14 literature.
  15
  16 A view for the \gls{mTask}-\gls{EDSL} is a type of kind \CI{*->*->*} that
  17 implements some of the classes given. The types do not have to be present as
  18 fields in the higher kinded view and can, and will most often, solely be
  19 phantom types. A view is of the form \CI{v t r}. The first variable will be the
  20 type of the view, the second type variable will be the type of the
  21 \gls{EDSL}-expression and the third type variable represents the role of the
  22 expression. Currently the role of the expressions form a hierarchy. The three
  23 roles and their hierarchy are shown in Listing~\ref{lst:exprhier}. This implies
  24 that everything is a statement, only a \CI{Upd} and a \CI{Expr} are
  25 expressions. The \CI{Upd} restriction describes updatable expressions such as
  26 \gls{GPIO} pins and \gls{SDS}.
  27
  28 \begin{lstlisting}[%
  29         language=Clean,label={lst:exprhier},caption={Expression role hierarchy}]
  30 :: Upd   = Upd
  31 :: Expr  = Expr
  32 :: Stmt  = Stmt
  33
  34 class isExpr a :: a -> Int
  35 instance isExpr Upd
  36 instance isExpr Expr
  37 \end{lstlisting}
  38
  39 \subsection{Expressions}
  40 Expressions in the \gls{mTask}-\gls{EDSL} are divided into two types, namely
  41 boolean expressions and arithmetic expressions. The class of arithmetic
  42 language constructs also contains the function \CI{lit} that lifts a
  43 host-language value in to the \gls{EDSL} domain. All standard arithmetic
  44 functions are included but are omitted for brevity. Moreover the class
  45 restrictions are only shown in the first functions and are later omitted. Both
  46 the boolean expression and arithmetic expression classes are shown in
  47 Listing~\ref{lst:arithbool}.
  48
  49 \begin{lstlisting}[language=Clean,label={lst:arithbool},
  50         caption={Basic classes for expressions}]
  51 class arith v where
  52   lit           :: t -> v t Expr
  53   (+.) infixl 6 :: (v t p) (v t q) -> v t Expr          | +, zero t    & isExpr p & isExpr q
  54   (-.) infixl 6 :: (v t p) (v t q) -> v t Expr          | -, zero t    & ...
  55   ...
  56 class boolExpr v where
  57   Not           :: (v Bool p) -> v Bool Expr            | ...
  58   (&.) infixr 3 :: (v Bool p) (v Bool q) -> v Bool Expr | ...
  59   ...
  60   (==.) infix 4 :: (v a p) (v a q) -> v Bool Expr       | ==, toCode a & ...
  61 \end{lstlisting}
  62
  63 \subsection{Control flow}
  64 \todo{Write this}
  65
  66 \subsection{Input/Output and class extensions}
  67 All expressions that have an \CI{Upd} role can be assigned to. Examples of such
  68 expressions are \glspl{SDS} and \gls{GPIO}. Moreover, class extensions can be
  69 created for specific peripherals such as user LEDs. The classes facilitating
  70 this are shown in Listing~\ref{lst:sdsio}. In this way the assignment is the
  71 same for every assignable entity.
  72
  73 \begin{lstlisting}[%
  74         language=Clean,label={lst:sdsio},caption={Input/Output classes}]
  75 :: DigitalPin = D0 | D1 | D2 | D3 | D4 | D5 |D6 | D7 | D8 | D9 | D10 | D11 | D12 | D13
  76 :: AnalogPin  = A0 | A1 | A2 | A3 | A4 | A5
  77 :: UserLED = LED1 | LED2 | LED3
  78
  79 class dIO v where dIO :: DigitalPin -> v Bool Upd
  80 class aIO v where aIO :: AnalogPin -> v Int Upd
  81 class analogRead v where
  82   analogRead :: AnalogPin -> v Int Expr
  83   analogWrite :: AnalogPin (v Int p) -> v Int Expr
  84 class digitalRead v where
  85   digitalRead :: DigitalPin -> v Bin Expr
  86   digitalWrite :: DigitalPin (v Bool p) -> v Int Expr
  87
  88 :: UserLED = LED1 | LED2 | LED3
  89 class userLed v where
  90   ledOn  :: (v UserLED q) -> (v () Stmt)
  91   ledOff :: (v UserLED q) -> (v () Stmt)
  92
  93 class assign v where
  94   (=.) infixr 2 :: (v t Upd) (v t p) -> v t Expr | ...
  95 \end{lstlisting}
  96
  97 A way of storing data in \glspl{mTask} is using \glspl{SDS}. \glspl{SDS} serve
  98 as variables in the \gls{mTask} and will keep their value across executions.
  99 The classes associated with \glspl{SDS} are listed in
 100 Listing~\ref{lst:sdsclass}. The \CI{Main} class is introduced to box an
 101 \gls{mTask} and make it recognizable by the type system.
 102
 103 \begin{lstlisting}[%
 104         language=Clean,label={lst:sdsclass},caption={\glspl{SDS} in \gls{mTask}}]
 105 :: In a b = In infix 0 a b
 106 :: Main a = {main :: a}
 107
 108 class sds v where
 109   sds :: ((v t Upd)->In t (Main (v c s))) -> (Main (v c s)) | ...
 110 \end{lstlisting}
 111
 112 \subsection{Example \gls{mTask}}
 113 \todo{Also explain semantics about running tasks}
 114 Some example \glspl{mTask} using almost all of the functionality are show in
 115 Listing~\ref{lst:exmtask}. The \glspl{mTask} shown in the example do not belong
 116 to a particular view and therefore are of the type \CI{View t r}. The
 117 \CI{blink} \gls{mTask} show the classic \emph{Arduino} \emph{Hello World!}
 118 application that blinks a certain LED every interval. The \CI{thermostat}
 119 \gls{mTask} will enable a digital pin powering a cooling fan when the analog
 120 pin representing a temperature sensor is too high. \CI{thermostat`} shows the
 121 same program but now using the assignment style \gls{GPIO}.
 122
 123 \begin{lstlisting}[%
 124         language=Clean,label={lst:exmtask},caption={Some example \glspl{mTask}}]
 125 blink :: Main (View Int Stmt)
 126 blink = sds \x=1 In sds \led=LED1 In {main =
 127   IF (x ==. lit 1) (ledOn led) (ledOff led) :.
 128   x =. lit 1 -. x
 129   }
 130
 131 thermostat :: Main (View () Stmt)
 132 thermostat = {main =
 133   IF (analogRead A0 >. 50)
 134         ( digitalWrite D0 (lit True)  )
 135     ( digitalWrite D0 (lit False) )
 136   }
 137
 138 thermostat` :: Main (View () Stmt)
 139 thermostat` = let
 140   a0 = aIO A0
 141   d0 = dIO D0 in {main = IF (a0 >. 50) (d0 =. lit True) (d0 =. lit False) }
 142 \end{lstlisting}