+\begin{lstlisting}[label={lst:controlflow},%
+ caption={Bytecode view for \texttt{arith}}]
+freshlabel = get >>= \st=:{freshl}->put {st & freshl=freshl+1} >>| pure freshl
+
+instance If ByteCode Stmt Stmt Stmt where If b t e = BCIfStmt b t e
+instance If ByteCode e Stmt Stmt where If b t e = BCIfStmt b t e
+instance If ByteCode Stmt e Stmt where If b t e = BCIfStmt b t e
+instance If ByteCode x y Stmt where If b t e = BCIfStmt b t e
+instance IF ByteCode where
+ IF b t e = BCIfStmt b t e
+ (?) b t = BCIfStmt b t (tell` [])
+BCIfStmt (BC b) (BC t) (BC e) = BC (
+ freshlabel >>= \else->freshlabel >>= \endif->
+ b >>| tell [BCJmpF else] >>|
+ t >>| tell [BCJmp endif, BCLab else] >>|
+ e >>| tell [BCLab endif]
+ )
+instance noOp ByteCode where
+ noOp = tell` [BCNop]
+\end{lstlisting}
+
+\subsection{Shared Data Sources \& Assignment}
+Shared data sources must be acquired from the state and constructing one
+involves multiple steps. First, a fresh identifier is grabbed from the state.
+Then a \CI{BCShare} record is created with that identifier. A \CI{BCSdsFetch}
+instruction is written and the body is generated to finally add the \gls{SDS}
+to the actual state with the value obtained from the function. The exact
+implementation is shown in Listing~\ref{lst:shareview}.
+
+\begin{lstlisting}[label={lst:shareview},%
+ caption={Bytecode view for \texttt{arith}}]
+freshshare = get >>= \st=:{freshs}->put {st & freshs=freshs+1} >>| pure freshs
+
+instance sds ByteCode where
+ sds f = {main = BC (freshshare
+ >>= \sdsi->pure {BCShare|sdsi=sdsi,sdsval=BCValue 0}
+ >>= \sds->pure (f (tell` [BCSdsFetch sds]))
+ >>= \(v In bdy)->modify (addSDS sds v)
+ >>| unBC (unMain bdy))
+ }
+instance sdspub ByteCode where
+ pub (BC x) = BC (censor (\[BCSdsFetch s]->[BCSdsPublish s]) x)
+
+addSDS sds v s = {s & sdss=[{sds & sdsval=BCValue v}:s.sdss]}
+\end{lstlisting}
+
+All assignable types compile to a \gls{RWST} that writes one fetch instruction.
+For example, using a \gls{SDS} always results in an expression of the form
+\CI{sds \x=4 In ...}. The actual \CI{x} is the \gls{RWST} that always writes
+one \CI{BCSdsFetch} instruction with the correct \gls{SDS} embedded. Assigning
+to an analog pin will result in the \gls{RWST} containing the \CI{BCAnalogRead}
+instruction. When the assignable is not a read from but assigned to, the
+instruction will be rewritten as a store instruction. Resulting in an
+\CI{BCSdsStore} or \CI{BCAnalogWrite} instruction respectively. The
+implementation for this is given in Listing~\ref{lst:assignmentview}.
+
+\begin{lstlisting}[label={lst:assignmentview},%
+ caption={Bytecode view implementation for assignment.}]
+instance assign ByteCode where
+ (=.) (BC v) (BC e) = BC (e >>| censor makeStore v)
+
+makeStore [BCSdsFetch i] = [BCSdsStore i]
+makeStore [BCDigitalRead i] = [BCDigitalWrite i]
+makeStore [...] = [...]
+\end{lstlisting}
+
+\section{Actual Compilation}
+All the previous functions are tied together with the \CI{toMessages} function.
+This function compiles the bytecode and transforms the \gls{Task} in a message.
+The \glspl{SDS} that were not already sent to the device are also added as
+messages to be sent to the device. This functionality is listed in
+Listing~\ref{lst:compilation}. The compilation process consists of two steps.
+First, the \gls{RWST} is executed. Then, the \emph{Jump} statements that
+jump to labels are transformed to jump to program memory addresses. The
+translation of labels is possible in one sweep because no labels are reused.
+Reusing labels would not give a speed improvement since the labels are removed
+anyway in the end.
+
+\begin{lstlisting}[label={lst:compilation},%
+ caption={Actual compilation.}]
+bclength :: BC -> Int
+bclength (BCPush s) = 1 + size (toByteCode s)
+bclength ... = ...
+bclength x = 1 + consNum{|*|} x
+
+computeGotos :: [BC] Int -> ([BC], Map Int Int)
+computeGotos [] _ = ([], newMap)
+computeGotos [BCLab l:xs] i = appSnd ('DM'.put l i) (computeGotos xs i)
+computeGotos [x:xs] i = appFst (\bc->[x:bc]) (computeGotos xs (i + bclength x))
+
+toRealByteCode :: (ByteCode a b) BCState -> (String, BCState)
+toRealByteCode x s
+# (s, bc) = runBC x s
+# (bc, gtmap) = computeGotos bc 1
+= (concat (map (toString o toByteVal) (map (implGotos gtmap) bc)), s)
+
+toMessages :: MTaskInterval (Main (ByteCode a b)) BCState -> ([MTaskMSGSend], BCState)
+toMessages interval x oldstate
+# (bc, newstate) = toRealByteCode (unMain x) oldstate
+# newsdss = difference newstate.sdss oldstate.sdss
+= ([MTSds sdsi e\\{sdsi,sdsval=e}<-newsdss] ++ [MTTask interval bc], newstate)
+\end{lstlisting}
+
+\section{Example}
+The heating example given previously in Listing~\ref{lst:exmtask} would be
+compiled to the following code. The left column indicates the
+position in the program memory.
+
+\begin{lstlisting}[caption={Thermostat bytecode},language=c]
+ 1-2 : BCAnalogRead (Analog A0)
+ 3-6 : BCPush (Int 50)
+ 7 : BCGre
+ 8-9 : BCJmpF 17 //Jump to else
+10-12: BCPush (Bool 1)
+13-14: BCDigitalWrite (Digital D0)
+15-16: BCJmp 21 //Jump to end of if
+17-19: BCPush (Bool 0) //Else label
+20 : BCDigitalWrite (Digital D0)
+\end{lstlisting}
+
+\section{Interpreter}
+The client contains an interpreter to execute a \gls{Task}'s bytecode.
+
+Before execution some preparatory work is done. The stack will be initialized
+and the program counter and stack pointer are set to zero and the bottom
+respectively. Then, the interpreter executes one step at the time while the
+program counter is smaller than the program length. The code for this is listed
+in Listing~\ref{lst:interpr}. One execution step is basically a big switch
+statement going over all possible bytecode instructions. Some instructions are
+detailed upon in the listing. The \CI{BCPush} instruction is a little more
+complicated in real life because some decoding will take place as not all
+\CI{BCValue}'s are of the same length.
+
+\begin{lstlisting}[language=C,label={lst:interpr},%
+ caption={Rough code outline for interpretation}]
+#define f16(p) program[pc]*265+program[pc+1]
+
+void run_task(struct task *t){
+ uint8_t *program = t->bc;
+ int plen = t->tasklength;
+ int pc = 0;
+ int sp = 0;
+ while(pc < plen){
+ switch(program[pc++]){
+ case BCNOP:
+ break;
+ case BCPUSH:
+ stack[sp++] = pc++ //Simplified
+ break;
+ case BCPOP:
+ sp--;
+ break;
+ case BCSDSSTORE:
+ sds_store(f16(pc), stack[--sp]);
+ pc+=2;
+ break;
+ // ...
+ case BCADD: trace("add");
+ stack[sp-2] = stack[sp-2] + stack[sp-1];
+ sp -= 1;
+ break;
+ // ...
+ case BCJMPT: trace("jmpt to %d", program[pc]);
+ pc = stack[--sp] ? program[pc]-1 : pc+1;
+ break;
+}
+\end{lstlisting}