
diff -r d8f870aad77d -r e7e7fe274f5c hws/hw09.tex
--- a/hws/hw09.tex	Wed Dec 21 14:33:05 2022 +0000
+++ b/hws/hw09.tex	Tue Apr 04 22:31:09 2023 +0100
@@ -2,6 +2,7 @@
 \usepackage{../style}
 \usepackage{../graphics}
 \usepackage{../langs}
+\usepackage{../grammar}
 
 \begin{document}
 
@@ -92,6 +93,25 @@
 }
 \end{lstlisting}
 
+\item As an optimisation technique, a compiler might want to detect `dead code' and
+  not generate anything for this code. Why does this optimisation technique have the
+  potential of speeding up the run-time of a program? (Hint: On what CPUs are programs
+  run nowadays?)
+
+\item In an earlier question, we analysed the advantages of having a lexer-phase
+  before running the parser (having a lexer is definitely a good thing to have). But you
+  might wonder if a lexer can also be implemented by a parser and some simple
+  grammar rules. Consider for example:
+
+  \begin{plstx}[margin=1cm]
+    : \meta{S\/} ::= (\meta{Kw\/}\mid \meta{Id\/}\mid \meta{Ws\/}) \cdot \meta{S\/} \;\mid\; \epsilon\\
+    : \meta{Kw\/} ::= \texttt{if} \mid \texttt{then} \mid \ldots\\
+    : \meta{Id\/} ::= (\texttt{a} \mid\ldots\mid \texttt{z}) \cdot \meta{Id\/} \;\mid\; \epsilon\\
+    : \meta{Ws\/} ::= \ldots\\
+  \end{plstx}
+
+  What is wrong with implementing a lexer in this way?
+
 \item What is the difference between a parse tree and an abstract
   syntax tree? Give some simple examples for each of them.
 




