
diff -r d82c91f85391 -r 258e18af6d14 cws/cw03.tex
--- a/cws/cw03.tex	Fri Oct 11 19:13:00 2024 +0100
+++ b/cws/cw03.tex	Wed Oct 16 13:14:13 2024 +0100
@@ -12,12 +12,22 @@
 
 \noindent This coursework is worth 10\% and is due on \cwTHREE{} at
 16:00. You are asked to implement a parser for the WHILE language and
-also an interpreter. The parser needs to use parser combinators.
-You can do the implementation in any programming
-language you like, but you need to submit the source code with which
-you answered the questions, otherwise a mark of 0\% will be
-awarded. You should use the lexer from the previous coursework for the
-parser.  Please submit your code to Github by the deadline.
+also an interpreter. The parser needs to use parser combinators.  You
+can do the implementation in any programming language you like, but
+you need to submit the source code with which you answered the
+questions, otherwise a mark of 0\% will be awarded. If you use Scala
+in your code, a good place to start is the file \texttt{comb1.sc} and
+\texttt{comb2.sc} uploaded to KEATS. Feel free to use the ``hack''
+explained during the lectures. This might make your grammar
+simpler. However, make sure you understand the code involved in the
+``hack'' because if you just do ``mix-and-match'' you will receive
+strange errors.  The main function that will be tested is called
+\texttt{eval} and \texttt{Stmts.parse\_all}. The latter expects a list
+of tokens as input and generates an AST. The former expects an AST and
+``runs'' the program. The marks will be distributed such that 6 marks
+are given for the correct grammar (and parsers); 4 marks for the correct
+\texttt{eval} function.  You should use the lexer from CW2 for the
+parser - you potentially need to make additions for CW2.  
 
 \subsection*{Disclaimer\alert}
 
@@ -29,6 +39,29 @@
 be tempted to ask Github Copilot for help or do any other
 shenanigans like this!
 
+\subsection*{Syntax Error in Template File cw03.sc\alert}
+
+Apologies, there is a small syntax error in the template file where a variable
+needs to be called \texttt{tks} instead of \texttt{tk}. The code
+in question is at the end of \texttt{cw03.sc} and should be like
+this (see lines 5, 6 and 8):
+
+\begin{lstlisting}[language=Scala,numbers=left]
+@main
+def test(file: String) = {
+  val contents = os.read(os.pwd / "examples" / file)
+  println(s"Lex $file: ")
+  val tks = tokenise(contents)
+  println(tks.mkString(","))
+  println(s"Parse $file: ")
+  val ast = Stmts.parse_all(tks).head
+  println(ast)
+  println(s"Eval $file: ")
+  println(eval(ast))
+}
+\end{lstlisting}  
+
+
 
 \subsection*{Question 1}
 
@@ -54,21 +87,13 @@
 \subsection*{Question 2}
 
 You should implement a parser for the WHILE language using parser
-combinators. Be careful that the parser takes as input a stream, or
-list, of \emph{tokens} generated by the tokenizer from the previous
+combinators. Be careful that the parser takes as input a list of
+\emph{tokens} generated by the tokenizer from the previous
 coursework. For this you might want to filter out whitespaces and
 comments. Your parser should be able to handle the WHILE programs in
-Figures~\ref{fib} -- \ref{collatz}.  In addition give the
-parse tree according to your grammar for the statement:
-
-\begin{lstlisting}[language=While,numbers=none]
-if (a < b) then skip else a := a * b + 1
-\end{lstlisting}
-
-\noindent
-The output of the parser is an abstract syntax tree (AST).
-A (possibly incomplete) datatype for ASTs of the WHILE language
-is shown in Figure~\ref{trees}.
+the \texttt{examples} directory.  The output of the parser is an
+abstract syntax tree (AST).  A (possibly incomplete) datatype for ASTs
+of the WHILE language is shown in Figure~\ref{trees}.
 
 \begin{figure}[p]
 \begin{lstlisting}[language=Scala]
@@ -133,8 +158,8 @@
 Note also that some programs contain a read-statement,
 which means you need to read and integer from the commandline
 and store the value in the corresponding variable.
-Programs you should be able to run are shown in
-Figures \ref{fib} -- \ref{collatz}. The output
+Programs you should be able to run are given in  the
+\texttt{examples} directory. The output
 of the \texttt{primes.while} should look as follows:
 
 \begin{figure}[h]
@@ -170,79 +195,6 @@
 \caption{Sample output for the file \texttt{primes.while}.\label{fib}}
 \end{figure}
 
-\noindent
-Give some time measurements for your interpreter
-and the loop program in Figure~\ref{loop}. For example
-how long does your interpreter take when \pcode{start}
-is initialised with 100, 500 and so on. How far can
-you scale this value if you are willing to wait, say
-1 Minute?
-
-\clearpage
-
-\begin{figure}[h]
-\lstinputlisting[language=while,xleftmargin=20mm]{../cwtests/cw03/fib.while}
-\caption{Fibonacci program in the WHILE language.\label{fib}}
-\end{figure}
-
-\begin{figure}[h]
-\lstinputlisting[language=while,xleftmargin=20mm]{../cwtests/cw03/loops.while}
-\caption{The three-nested-loops program in the WHILE language. 
-Usually used for timing measurements.\label{loop}}
-\end{figure}
-
-\begin{figure}[h]
-\lstinputlisting[language=while,xleftmargin=0mm]{../cwtests/cw03/primes.while}
-\caption{Prime number program.\label{primes}}
-\end{figure}
-
-
-\begin{figure}[p]
-\lstinputlisting[language=while,xleftmargin=0mm]{../cwtests/cw03/collatz2.while}
-\caption{Collatz series program.\label{collatz}}
-\end{figure}
-
-\clearpage
-\newpage
-\section*{Answers}
-
-\mbox{}  
-
-\noindent
-\textbf{Name:}\uline{\hfill}\bigskip
-
-
-
-\noindent
-\textbf{Question 1 (Grammar):}\\
-
-\mbox{}\\[9cm]
-
-\newpage
-\noindent
-\textbf{Question 2 (Parse Tree):}\\
-
-\mbox{}\\[8cm]
-
-
-\noindent
-\textbf{Question 3 (Timings):}\\
-
-\begin{center}
-  \def\arraystretch{1.5}
-  \begin{tabular}{l|l}
-    n & secs\\
-    \hline
-    100 & \\
-    500 & \\
-    700 & \\
-    1000 & \\
-    \\
-    \\
-    \\
-    \\
-   \end{tabular} 
-\end{center}  
 
 \end{document}
 




