\documentclass{article}

\usepackage{../style}

\usepackage{../langs}

\usepackage{../graphics}

\begin{document}

\section*{Homework 8}

%%\HEADER

\begin{enumerate}

\item Write a program in the WHILE-language that calculates

      the factorial function.

\item What optimisations could a compiler perform when

      compiling a WHILE-program?

\item What is the main difference between the Java assembler

      (as processed by Jasmin) and Java Byte Code?

\item Remember symbolic labels in the Jasmin-assembler are meant to

      be used for jumps (like in loops or if-conditions). Assume

      you generated a Jasmin-file with some redundant

      labels, that is some labels are not used in your code for any jumps. For

      example \texttt{L\_begin} and \texttt{L\_end} are not used

      in the fol,lowing code-snippet:

\begin{lstlisting}[language=JVMIS,numbers=none]

L_begin:        

ldc 1

ldc 2

ldc 3

imul

ldc 4

ldc 3

isub

iadd

iadd

L_end:

\end{lstlisting}

      Do these redundant labels affect the size of the generated

      JVM-code? (Hint: What are the labels translated to by

      the Jasmin-assembler?).

      \solution{The answer is no. The reason is that assemblers

        calculate for labels either relative or explicit adresses,

        which are then used in the JVM-byte-code. Relative addresses

        are like ``jump 10 bytes forward'' or ``12 bytes backward''. So

      additional labels do not increase the size of the generated code.}

\item Consider the following Scala snippet. Are the two functions

\texttt{is\_even} and \texttt{is\_odd} tail-recursive?     

\begin{lstlisting}[numbers=none]

def is_even(n: Int) : Boolean = {

    if (n == 0) true else is_odd(n - 1)

}

def is_odd(n: Int) : Boolean = {

    if (n == 0) false 

    else if (n == 1) true else is_even(n - 1)

}

\end{lstlisting}

Do they cause stack-overflows when compiled to the JVM (for example by Scala)?

\item Explain what is meant by the terms lazy evaluation and eager

  evaluation.

\item \POSTSCRIPT    

\end{enumerate}

\end{document}

%%% Local Variables: 

%%% mode: latex

%%% TeX-master: t

%%% End: