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\section*{Coursework 3}

\noindent

This coursework is worth 4\% and is due on 13 December at 16:00. You are asked to 

implement a compiler for the WHILE language that targets the

assembler language provided by the Jasmin. This assembler 

is available from

\begin{center}

\url{http://jasmin.sourceforge.net}

\end{center}

\noindent

There is a user guide for Jasmin

\begin{center}

\url{http://jasmin.sourceforge.net/guide.html}

\end{center}

\noindent

and also a description of some of the instructions that the JVM understands

\begin{center}

\url{http://jasmin.sourceforge.net/instructions.html}

\end{center}

\noindent

\noindent

You need to submit a document containing the answers for the two questions 

below. You can do the implementation in any programming language you like, but you need 

will \emph{only} be judged according to the answers. You can submit your answers

in a txt-file or as pdf.\bigskip

\subsection*{Question 1 (marked with 2\%)}

You need to lex and parse WHILE programs and submit the assembler 

instructions for the Fibonacci program and for the program you submitted

in Coursework 2 in Question 3. The latter should be so modified that 

a user can input the upper bound on the console (in the original question

it was fixed to 100).

\subsection*{Question 2 (marked with 2\%)}

Extend the syntax of you language so that it contains also \texttt{for}-loops, like

\begin{center}

\texttt{for} \;\textit{Id} \texttt{:=} \textit{AExp}\; \texttt{upto} \;\textit{AExp}\; \texttt{do} \textit{Block} 

\end{center}

\noindent

The intended meaning is to first assign the variable \textit{Id} the value of the first arithmetic 

expression, then go through the loop, at the end increase the value of the variable by 1, 

and finally test wether the value is not less or equal anymore to the value of the second

arithmetic expression. For example the following instance of a \texttt{for}-loop 

is supposed to print out the numbers \texttt{2}, \texttt{3}, \texttt{4}.

\begin{center}

\begin{minipage}{6cm}

\begin{lstlisting}[language=While,basicstyle=\ttfamily, numbers=none]

for i := 2 upto 4 do {

    write i	

}

\end{lstlisting}

\end{minipage}

\end{center}

\noindent

There are two ways how this can be implemented: one is to adapt the code generation 

part of the compiler and generate specific code for \texttt{for}-loops; the other is to

translate the abstract syntax tree of \texttt{for}-loops into an abstract syntax tree using

existing language constructs. For example the loop above could be translated

to the following \texttt{while}-loop:

\begin{center}

\begin{minipage}{6cm}

\begin{lstlisting}[language=While,basicstyle=\ttfamily, numbers=none]

i := 2;

while (i <= 4) do {

    write i;

    i := i + 1;

}

\end{lstlisting}

\end{minipage}

\end{center}

\subsection*{Further Information}

The Java infrastructure unfortunately does not contain an assembler out-of-the-box

(therefore

you need to download the additional package Jasmin---see above). But it does contain a 

disassembler, called \texttt{javap}. A dissembler does the ``opposite'' of an assembler: it

generates readable assembler code from Java Byte Code. Have a look at the

following example. Compile using the usual Java compiler, 

\texttt{java}, the simple Hello World program below:

\begin{center}

\begin{minipage}{10cm}

\begin{lstlisting}[language=Java,basicstyle=\ttfamily]

class HelloWorld {

    public static void main(String[] args) {

        System.out.println("Hello World!");

    }

}

\end{lstlisting}

\end{minipage}

\end{center}

\noindent

You can use the command

\begin{center}

\texttt{javap -v HelloWorld}

\end{center}

\noindent

in order to see which Java Byte Code has been generated for this

program. You can compare this with the code generated for the Scala

version of Hello Worlds.

\begin{center}

\begin{minipage}{10cm}

\begin{lstlisting}[language=Scala,basicstyle=\ttfamily]

object HelloWorld {

   def main(args: Array[String]) {

      println("Hello World!")

  }

}

\end{lstlisting}

\end{minipage}

\end{center}

\end{document}

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