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\begin{document}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}<1>[t]

\frametitle{%

  \begin{tabular}{@ {}c@ {}}

  \\[-3mm]

  \LARGE Automata and \\[-2mm] 

  \LARGE Formal Languages (7)\\[3mm] 

  \end{tabular}}

  \normalsize

  \begin{center}

  \begin{tabular}{ll}

  Email:  & christian.urban at kcl.ac.uk\\

  Of$\!$fice: & S1.27 (1st floor Strand Building)\\

  Slides: & KEATS (also home work is there)\\

  \end{tabular}

  \end{center}

\end{frame}}

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}[t]

\frametitle{\begin{tabular}{c}\bl{$(a?\{n\})a\{n\}$}\end{tabular}}

\mbox{}\\[-13mm]

\begin{tikzpicture}[y=.2cm, x=.3cm]

 	%axis

	\draw (0,0) -- coordinate (x axis mid) (30,0);

    	\draw (0,0) -- coordinate (y axis mid) (0,30);

    	%ticks

    	\foreach \x in {0,5,...,30}

     		\draw (\x,1pt) -- (\x,-3pt)

			node[anchor=north] {\x};

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     		\draw (1pt,\y) -- (-3pt,\y) 

     			node[anchor=east] {\y}; 

	%labels      

	\node[below=0.6cm] at (x axis mid) {\bl{a}s};

	\node[rotate=90, left=1.2cm] at (y axis mid) {secs};

	%plots

	\draw[color=blue] plot[mark=*, mark options={fill=white}] 

		file {re-python.data};

	\draw[color=red] plot[mark=triangle*, mark options={fill=white} ] 

		file {re1.data};

         \draw[color=green] plot[mark=square*, mark options={fill=white} ] 

		file {re2.data};

         \draw[color=brown] plot[mark=pentagon*, mark options={fill=white} ] 

		file {re-ruby.data};

	%legend

	\begin{scope}[shift={(4,20)}] 

	\draw[color=blue] (0,0) -- 

		plot[mark=*, mark options={fill=white}] (0.25,0) -- (0.5,0) 

		node[right]{\small Python};

	\draw[yshift=-\baselineskip, color=brown] (0,0) -- 

		plot[mark=pentagon*, mark options={fill=white}] (0.25,0) -- (0.5,0)

		node[right]{\small Ruby (Daniel Baldwin)};

         \draw[yshift=\baselineskip, color=red] (0,0) -- 

		plot[mark=triangle*, mark options={fill=white}] (0.25,0) -- (0.5,0)

		node[right]{\small Scala V1};	

	 \draw[yshift=2\baselineskip, color=green] (0,0) -- 

		plot[mark=square*, mark options={fill=white}] (0.25,0) -- (0.5,0)

		node[right]{\small Scala V2 with simplifications};

	\end{scope}

\end{tikzpicture}

\end{frame}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}[t]

\begin{tikzpicture}[y=.7cm, x=.0009cm]

 	%axis

	\draw (0,0) -- coordinate (x axis mid) (10000,0);

    	\draw (0,0) -- coordinate (y axis mid) (0,6);

    	%ticks

    	\foreach \x in {0,2000,...,10000}

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			node[anchor=north] {\x};

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     			node[anchor=east] {\y}; 

	%labels      

	\node[below=0.6cm] at (x axis mid) {\bl{a}s};

	\node[rotate=90, left=1.2cm] at (y axis mid) {secs};

	%plots

	\draw[color=blue] plot[mark=*, mark options={fill=white}] 

		file {re-internal.data};

	\only<1->{	 

         \draw[color=red] plot[mark=triangle*, mark options={fill=white} ] 

		file {re3.data};}

	%legend

	\begin{scope}[shift={(2000,4)}] 

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		node[right]{\small Scala Internal};

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		node[right]{\small Scala V3 with explicit $\_\{\_\}$};}

	\end{scope}

\end{tikzpicture}

\begin{center}

\begin{tabular}{@ {}l@ {\hspace{2mm}}c@ {\hspace{2mm}}l@ {\hspace{-10mm}}l@ {}}

  \\[-8mm]

  \bl{der c (r$_1$ $\cdot$ r$_2$)} & \bl{$\dn$}  & \bl{if nullable r$_1$}\\

  & & \bl{then ((der c r$_1$) $\cdot$ r$_2$) + (der c r$_2$)}\\ 

  & & \bl{else (der c r$_1$) $\cdot$ r$_2$}\\

  \bl{der c (r$\{n\}$)} & \bl{$\dn$} & \bl{if $n = 0$ then $\varnothing$}\\

  & & \bl{else (der c r) $\cdot$ r$\{n - 1\}$}

  \end{tabular}

\end{center}

\end{frame}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

\newcommand{\qq}{\mbox{\texttt{"}}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}CFG\end{tabular}}

A \alert{context-free} grammar \bl{$G$} consists of

\begin{itemize}

\item a finite set of nonterminal symbols (upper case)

\item a finite terminal symbols or tokens (lower case)

\item a start symbol (which must be a nonterminal)

\item a set of rules

\begin{center}

\bl{$A \rightarrow \text{rhs}$}

\end{center}

where \bl{rhs} are sequences involving terminals and nonterminals (can also be empty).\medskip\pause

We can also allow rules

\begin{center}

\bl{$A \rightarrow \text{rhs}_1 | \text{rhs}_2 | \ldots$}

\end{center}

\end{itemize}

\end{frame}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}A CFG Derivation\end{tabular}}

\begin{enumerate}

\item Begin with a string with only the start symbol \bl{$S$}\bigskip

\item Replace any non-terminal \bl{$X$} in the string by the
right-hand side of some production \bl{$X \rightarrow \text{rhs}$}\bigskip

\item Repeat 2 until there are no non-terminals

\end{enumerate}

\begin{center}

\bl{$S \rightarrow \ldots \rightarrow \ldots  \rightarrow \ldots  \rightarrow \ldots $}

\end{center}

\end{frame}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}Language of a CFG\end{tabular}}

Let \bl{$G$} be a context-free grammar with start symbol \bl{$S$}. 

Then the language \bl{$L(G)$} is:

\begin{center}

\bl{$\{c_1\ldots c_n \;|\; \forall i.\; c_i \in T \wedge S \rightarrow^* c_1\ldots c_n \}$}

\end{center}\pause

\begin{itemize}

\item Terminals are so-called because there are no rules for replacing them

\item Once generated, terminals are ``permanent''

\item Terminals ought to be tokens of the language (at least in this course)

\end{itemize}

\end{frame}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}Arithmetic Expressions\end{tabular}}

\begin{center}

\bl{\begin{tabular}{lcl}

$E$ & $\rightarrow$ &  $num\_token$ \\

$E$ & $\rightarrow$ &  $E \cdot + \cdot E$ \\

$E$ & $\rightarrow$ &  $E \cdot - \cdot E$ \\

$E$ & $\rightarrow$ &  $E \cdot * \cdot E$ \\

$E$ & $\rightarrow$ &  $( \cdot E \cdot )$ 

\end{tabular}}

\end{center}\pause\bigskip

A CFG is \alert{left-recursive} if it has a nonterminal \bl{$E$} such

that \bl{$E \rightarrow^+ E\cdot \ldots$}

\end{frame}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}Parse Trees\end{tabular}}

\begin{center}

\bl{\begin{tabular}{lcl}

$E$ & $\rightarrow$ &  $F \;|\; F \cdot * \cdot F$\\

$F$ & $\rightarrow$ & $T \;|\; T \cdot + \cdot T \;|\; T \cdot - \cdot T$\\

$T$ & $\rightarrow$ & $num\_token \;|\; ( \cdot E \cdot )$\\

\end{tabular}}

\end{center}

\begin{center}

\begin{tikzpicture}[level distance=8mm, blue]

  \node {$E$}

    child {node {$F$} 

     child {node {$T$} 

                 child {node {(\,$E$\,)}

                            child {node{$F$ *{} $F$}

                                  child {node {$T$} child {node {2}}}

                                  child {node {$T$} child {node {3}}} 

                               }

                          }

              }

     child {node {+}}

     child {node {$T$}

       child {node {(\,$E$\,)} 

       child {node {$F$}

       child {node {$T$ +{} $T$}

                    child {node {3}}

                    child {node {4}} 

                 }

                 }}

    }};

\end{tikzpicture}

\end{center}

\begin{textblock}{5}(1, 6.5)

\bl{\texttt{(2*3)+(3+4)}}

\end{textblock}

\end{frame}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}Ambiguous Grammars\end{tabular}}

A CFG is \alert{ambiguous} if there is a string that has at least parse trees.

\begin{center}

\bl{\begin{tabular}{lcl}

$E$ & $\rightarrow$ &  $num\_token$ \\

$E$ & $\rightarrow$ &  $E \cdot + \cdot E$ \\

$E$ & $\rightarrow$ &  $E \cdot - \cdot E$ \\

$E$ & $\rightarrow$ &  $E \cdot * \cdot E$ \\

$E$ & $\rightarrow$ &  $( \cdot E \cdot )$ 

\end{tabular}}

\end{center}

\bl{\texttt{1 + 2 * 3 + 4}}

\end{frame}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\mode<presentation>{

\begin{frame}[c]

\frametitle{\begin{tabular}{c}Dangling Else\end{tabular}}

Another ambiguous grammar:\bigskip

\begin{center}

\bl{\begin{tabular}{lcl}

$E$ & $\rightarrow$ &  if $E$ then $E$\\

 & $|$ &  if $E$ then $E$ else $E$ \\

 & $|$ &  id 

\end{tabular}}

\end{center}\bigskip