\documentclass[dvipsnames,14pt,t,xelatex]{beamer}

\usepackage{../slides}

\usepackage{../graphics}

\usepackage{../langs}

\usepackage{../data}

\hfuzz=220pt 

\lstset{language=Scala,

        style=mystyle,

        numbersep=0pt,

        numbers=none,

        xleftmargin=0mm}

\newcommand{\bl}[1]{\textcolor{blue}{#1}}     

% beamer stuff 

\renewcommand{\slidecaption}{CFL 01, King's College London}

\begin{document}

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\begin{frame}[t]

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

  \\[-3mm]

  \LARGE Compilers and \\[-1mm] 

  \LARGE Formal Languages (1)\\[-3mm] 

  \end{tabular}}

  \begin{center}

  %\includegraphics[scale=0.3]{pics/ante1.jpg}\hspace{5mm}

  %\includegraphics[scale=0.31]{pics/ante2.jpg}\\

  %\footnotesize\textcolor{gray}{Antikythera automaton, 100 BC (Archimedes?)}

  \end{center}

  \begin{center}

  \begin{tabular}{ll}

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

  Office: & N7.07 (North Wing, Bush House)\\

  Slides: & KEATS

  \end{tabular}

  \end{center}

\end{frame}

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\begin{frame}[c]

\frametitle{The Goal of this Course}

\begin{center}

  \begin{tikzpicture}[scale=1,

                      node/.style={

                      rectangle,rounded corners=3mm,

                      very thick,draw=black!50,minimum height=18mm, minimum width=20mm,

                      top color=white,bottom color=black!20}]

  \node at (3.05, 1.8) {\Large\bf Write A Compiler};

  \node (0) at (-2.3,0) {}; 

  \node (A) at (0,0)  [node] {};

  \node [below right] at (A.north west) {lexer};

  \node (B) at (3,0)  [node] {};

  \node [below right=1mm] at (B.north west) {\mbox{}\hspace{-1mm}parser};

  \node (C) at (6,0)  [node] {};

  \node [below right] at (C.north west) {\mbox{}\hspace{-1mm}code gen};

  \node (1) at (8.4,0) {}; 

  \draw [->,line width=4mm] (0) -- (A); 

  \draw [->,line width=4mm] (A) -- (B); 

  \draw [->,line width=4mm] (B) -- (C); 

  \draw [->,line width=4mm] (C) -- (1); 

  \end{tikzpicture}

  \end{center}

\only<2,3>{

\begin{textblock}{1}(1,2)

\begin{bubble}[9.8cm]

\normalsize

lexer input: a string\smallskip\\

\hspace{5mm}\code{"read(n);"}\medskip\\

lexer output: a sequence of tokens\smallskip\\

\hspace{5mm}\code{key(read); lpar; id(n); rpar; semi}

\end{bubble}

\end{textblock}}

\only<3>{

\begin{textblock}{1}(6,7.8)

\begin{tabular}{c}

\includegraphics[scale=0.2]{../pics/rosetta.jpg}\\[-2mm]

\footnotesize lexing $\Rightarrow$ recognising words (Stone of Rosetta)

\end{tabular}

\end{textblock}}

\only<4>{

\begin{textblock}{1}(1,1.5)

\begin{bubble}[8.5cm]

\normalsize

parser input: a sequence of token\smallskip\\

parser output: an abstract syntax tree\smallskip\\

\footnotesize

\hspace{2cm}\begin{tikzpicture}

  \node {\code{read}}

    child {node {\code{lpar}}}

    child {node {\code{n}}}

    child {node {\code{rpar}}};

\end{tikzpicture}

\end{bubble}

\end{textblock}}

\only<5,6>{

\begin{textblock}{1}(1,1.5)

\begin{bubble}[4cm]

\normalsize

code generator:\smallskip\\

\hspace{5mm}\code{istore 2}\\ 

\hspace{5mm}\code{iload 2}\\ 

\hspace{5mm}\code{ldc 10}\\

\hspace{5mm}\code{isub}\\

\hspace{5mm}\code{ifeq Label2}\\ 

\hspace{5mm}\code{iload 2}\\

\hspace{5mm}\code{...}\\

\end{bubble}

\end{textblock}}

\only<6>{

\begin{textblock}{6}(8.4,7)

\begin{bubble}[5cm]

\mbox{\begin{tikzpicture}[scale=0.58,rounded corners=0mm]

\begin{axis}[axis x line=bottom, axis y line=left, ylabel=secs,

    xlabel=n,

    enlargelimits=0.05,

    ybar interval=0.7, legend style=small]

\addplot file {interpreted2.data};

\addplot file {compiled2.data};

%\legend{interpreted, compiled}

\end{axis}

\end{tikzpicture}}

\end{bubble}

\end{textblock}}

\end{frame}

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\begin{frame}[c]

\frametitle{The subject is quite old}

\begin{itemize}

\item Turing Machines, 1936

\item Regular Expressions, 1956\\

\item The first compiler for COBOL, 1957\\ (Grace Hopper)

\item But surprisingly research papers are still published nowadays

\end{itemize}

\begin{flushright}

\includegraphics[scale=0.3]{pics/hopper.jpg}\\

\footnotesize\textcolor{gray}{Grace Hopper}

\end{flushright}

\mbox{}\\[-10mm]

{\footnotesize\textcolor{gray}{(she made it to David Letterman's Tonight Show, \url{http://www.youtube.com/watch?v=aZOxtURhfEU})}}

\end{frame}

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\begin{frame}[c]

\frametitle{Why Bother?}

\begin{columns}[t]

\begin{column}{.5\textwidth}

Ruby, Python, Java\medskip\\

\begin{tikzpicture}\footnotesize

\begin{axis}[

    xlabel={$n$},

    x label style={at={(1.05,0.0)}},

    ylabel={time in secs},

    enlargelimits=false,

    xtick={0,5,...,30},

    xmax=33,

    ymax=35,

    ytick={0,5,...,30},

    scaled ticks=false,

    axis lines=left,

    width=5.5cm,

    height=4cm, 

    legend entries={Python,Ruby},  

    legend pos=north west,

    legend cell align=left]

\addplot[blue,mark=*] table {re-python.data};

\addplot[brown,mark=triangle*] table {re-ruby.data};

\end{axis}

\end{tikzpicture}

\begin{tikzpicture}\footnotesize

\begin{axis}[

    xlabel={$n$},

    x label style={at={(1.05,0.0)}},

    ylabel={time in secs},

    enlargelimits=false,

    xtick={0,5,...,30},

    xmax=33,

    ymax=35,

    ytick={0,5,...,30},

    scaled ticks=false,

    axis lines=left,

    width=5.5cm,

    height=4cm, 

    legend entries={Java},  

    legend pos=north west,

    legend cell align=left]

\addplot[cyan,mark=*, mark options={fill=white}] table {re-java.data};

\end{axis}

\end{tikzpicture}

\end{column}

\begin{column}{.5\textwidth}

Us (after next lecture)\medskip\\

\begin{tikzpicture}\footnotesize

\begin{axis}[

    xlabel={$n$},

    x label style={at={(1.07,0.0)}},

    ylabel={time in secs},

    enlargelimits=false,

    xtick={0,5000,...,10000},

    xmax=11000,

    ymax=35,

    ytick={0,5,...,30},

    scaled ticks=false,

    axis lines=left,

    width=5.5cm,

    height=4cm]

\addplot[green,mark=square*,mark options={fill=white}] table {re2.data};

\addplot[black,mark=square*,mark options={fill=white}] table {re3.data};

\end{axis}

\end{tikzpicture}

\begin{tikzpicture}\footnotesize

\begin{axis}[

    xlabel={$n$},

    x label style={at={(1.07,0.0)}},

    ylabel={time in secs},

    enlargelimits=false,

    ymax=35,

    ytick={0,5,...,30},

    scaled ticks=false,

    axis lines=left,

    width=5.5cm,

    height=4cm]

\addplot[black,mark=square*,mark options={fill=white}] table {re3a.data};

\end{axis}

\end{tikzpicture}

\end{column}

\end{columns}\bigskip

\small\centering

matching \texttt{[a?]\{n\}[a]\{n\}} and \texttt{[a*]*b}

against $\underbrace{\texttt{a}...\texttt{a}}_n$

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\begin{frame}[c]

\frametitle{Lectures 1 - 5}

transforming strings into structured data\\[10mm]

{\LARGE\bf Lexing} {\hfill{}based on regular expressions}\medskip\\

\hspace{5mm}(recognising ``words'')\\[6mm]

{\LARGE\bf Parsing}\medskip\\

\hspace{5mm}(recognising ``sentences'')

\begin{textblock}{1}(10,9.1)

\begin{tabular}{c}

\includegraphics[scale=0.1]{../pics/rosetta.jpg}\\[-2mm]

\footnotesize Stone of Rosetta

\end{tabular}

\end{textblock}

\end{frame}

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\begin{frame}[t]

\frametitle{Familiar Regular Expr.}

\small

\begin{center}

\texttt{[a-z0-9\_.-]+ @ [a-z0-9.-]+ . [a-z.]\{2,6\}}

\end{center}\smallskip

\begin{center}

\begin{tabular}{@{}lp{8.5cm}@{}}

\pcode{re*} & matches 0 or more times\\

\pcode{re+} & matches 1 or more times\\

\pcode{re?} & matches 0 or 1 times\\

\pcode{re\{n\}}	& matches exactly \pcode{n} number of times\\

\pcode{re\{n,m\}} & matches at least \pcode{n} and at most {\tt m} times\\

\pcode{[...]} & matches any single character inside the brackets\\

\pcode{[^...]} & matches any single character not inside the 

brackets\\

\pcode{a-zA-Z} & character ranges\\

\pcode{\\d} & matches digits; equivalent to \pcode{[0-9]}\\

\pcode{.} & matches every character except newline\\

\pcode{(re)}	& groups regular expressions and remembers 

the matched text

\end{tabular}

\end{center}

\end{frame}

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\begin{frame}[c]

\frametitle{Today}

\begin{itemize}

\item While the ultimate goal is to implement a small compiler 

(a really small one for the JVM)\ldots\bigskip

\end{itemize}

Let's start with:

\begin{itemize}

\item a web-crawler

\item an email harvester

\item \textcolor{gray}{(a web-scraper)}

\end{itemize}

\end{frame}

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\begin{frame}[t]

\frametitle{A Web-Crawler}

\mbox{}\\[10mm]

\begin{enumerate}

\item given an URL, read the corresponding webpage

\item extract all links from it

\item call the web-crawler again for all these links

\end{enumerate}

\end{frame}

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\mode<presentation>{

\begin{frame}[t]

\frametitle{A Web-Crawler}

\mbox{}\\[10mm]

\begin{enumerate}

\item given an URL, read the corresponding webpage

\item if not possible print, out a problem

\item if possible, extract all links from it

\item call the web-crawler again for all these links

\end{enumerate}\bigskip\pause

\small (we need a bound for the number of recursive calls)

\small (the purpose is to check all links on my own webpage)

\end{frame}}

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\begin{frame}[c]

\begin{textblock}{1}(2,5)

\begin{tabular}{c}

\includegraphics[scale=0.15]{pics/servers.png}\\[-2mm]

\small Server

\end{tabular}

\end{textblock}

\begin{textblock}{1}(5.6,4)

  \begin{tikzpicture}[scale=1.1]

  \draw[white] (0,1) node (X) {};

  \draw[white] (2,1) node (Y) {};

   \draw[white] (0,0) node (X1) {};

  \draw[white] (2,0) node (Y1) {};

   \draw[white] (0,-1) node (X2) {};

  \draw[white] (2,-1) node (Y2) {};

  \draw[red, <-, line width = 2mm] (X) -- (Y);

  \node [inner sep=5pt,label=above:\textcolor{black}{GET request}] at ($ (X)!.5!(Y) $) {};

  \draw[red, ->, line width = 2mm] (X1) -- (Y1);

  \node [inner sep=5pt,label=above:\textcolor{black}{webpage}] at ($ (X1)!.5!(Y1) $) {};

  \draw[red, <-, line width = 2mm] (X2) -- (Y2);

  \node [inner sep=7pt,label=above:\textcolor{black}{POST data}] at ($ (X2)!.5!(Y2) $) {};

  \end{tikzpicture}

\end{textblock}

\begin{textblock}{1}(9,5.5)

\begin{tabular}{c}

\includegraphics[scale=0.15]{pics/laptop.png}\\[-2mm]

\small Browser

\end{tabular}

\end{textblock}

\end{frame}

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\begin{frame}[c]

\frametitle{Scala}

\small A simple Scala function for reading webpages:

\smallskip

\footnotesize

\lstinputlisting{../progs/app0.scala}

\medskip\pause

\lstinline{get_page("""http://www.inf.kcl.ac.uk/staff/urbanc/""")}

\bigskip\medskip\pause

\small A slightly more complicated version for handling errors:

\smallskip

\footnotesize

\lstinputlisting{../progs/app1.scala}

\end{frame}

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\begin{frame}[t]

\frametitle{A Regular Expression}

\begin{itemize}

\item \ldots{} is a pattern or template for specifying strings

\end{itemize}\bigskip

\begin{center}  

\only<1>{\scode{"https?://[^"]*"}}%

\only<2>{\scode{""""https?://[^"]*"""".r}}

\end{center}\bigskip\bigskip

matches for example\smallskip\\  

\hspace{2mm}\code{"http://www.foobar.com"}\\

\hspace{2mm}\code{"https://www.tls.org"}\\

\end{frame}

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\begin{frame}[t]

\frametitle{Finding Operations}

{\bf\code{rexp.findAllIn(string)}}\medskip

returns a list of all (sub)strings that match the 

regular expression

\bigskip\bigskip  

{\bf\code{rexp.findFirstIn(string)}}\medskip

returns either 

\begin{itemize}

\item \code{None} if no (sub)string matches or 

\item \code{Some(s)} with the first (sub)string

\end{itemize}

\end{frame}

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\begin{frame}[c]