\begin{frame}{Lexical Analysis}
  \begin{block}{}
    \emph{Lexical analysis} converts a sequence of \emph{characters}
    into a sequence of \emph{tokens}.
  \end{block}
  Programs that do lexical analysis are \emph{lexers} or \emph{tokenizers}.
  \pause
  
  \begin{exampleblock}{}
    For example the expression
    \begin{talign}
      \texttt{sum = 15 + 2}
    \end{talign}
    could be converted to the sequence of tokens
    \begin{center}
      {\renewcommand{\arraystretch}{1}
      \begin{tabular}{|l|l|}
        \hline
        token & token category \\
        \hline
        \texttt{sum} & identifier \\
        \hline
        \texttt{=} & assignment \\
        \hline
        \texttt{15} & integer literal \\
        \hline
        \texttt{+} & operator \\
        \hline
        \texttt{2} & integer literal \\
        \hline
      \end{tabular}}
    \end{center}
  \end{exampleblock}
  Allows to write parsers on the more abstract level of tokens. 
\end{frame}