--- a/slides08.tex	Wed Nov 21 02:34:37 2012 +0000
+++ b/slides08.tex	Wed Nov 21 07:28:28 2012 +0000
@@ -570,8 +570,6 @@
 \end{frame}}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
 
-
-
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \mode<presentation>{
 \begin{frame}[c]
@@ -585,6 +583,54 @@
 \end{frame}}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\mode<presentation>{
+\begin{frame}[c]
+\frametitle{\begin{tabular}{c}While-Language\end{tabular}}
+
+
+\begin{center}
+\bl{\begin{tabular}{lcl}
+$Stmt$ & $\rightarrow$ &  $\text{skip}$\\
+              & $|$ & $Id := AExp$\\
+              & $|$ & $\text{if}\; B\!Exp \;\text{then}\; Block \;\text{else}\; Block$\\
+              & $|$ & $\text{while}\; B\!Exp \;\text{do}\; Block$\bigskip\\
+$Stmt$ & $\rightarrow$ &  $Stmt \;\text{;}\; Stmts$\\
+              & $|$ & $Stmt$\bigskip\\
+$Block$ & $\rightarrow$ &  $\{ Stmts \}$\\
+                & $|$ & $Stmt$\\
+\end{tabular}}
+\end{center}
+
+
+\end{frame}}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\mode<presentation>{
+\begin{frame}[c]
+\frametitle{\begin{tabular}{c}An Interpreter\end{tabular}}
+
+\begin{center}
+\bl{\begin{tabular}{l}
+$\{$\\
+\;\;$x := 5 \text{;}$\\
+\;\;$y := x * 3\text{;}$\\
+\;\;$y := x * 4\text{;}$\\
+\;\;$x := u * 3$\\
+$\}$
+\end{tabular}}
+\end{center}
+
+\begin{itemize}
+\item the interpreter has to record the value of \bl{$x$} before assigning a value to \bl{$y$}\pause
+\item \bl{\text{eval}(stmt, env)}
+\end{itemize}
+
+
+\end{frame}}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+
 \end{document}
 
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