\section{Implementation}

\subsection{Engine}

An engine implementing GTP.\@ It is designed to be used by a software controller
but can also be directly run, mostly for debugging purposes. Its design is shown
in \fref{fig:engine}

\begin{figure}[h]
	\begin{center}
		\includegraphics[width=\textwidth]{diagrams/gtpEngine.png}
		\caption{Design of the GTP engine.}\label{fig:engine}
	\end{center}
\end{figure}

\subsection{Modules}

One module to store the state of the game and the game tree. One module to parse
moves. One module to read and write SGF files. Modules are shown in
\fref{fig:modules}.

\begin{figure}[h]
	\begin{center}
		\includegraphics[width=\textwidth]{diagrams/modules.png}
		\caption{Modules.}\label{fig:modules}
	\end{center}
\end{figure}

\subsection{Representation of a match}

Strictly said, a match is composed of a series of moves. But since game review
and variants exploration is an important part of Go learing, \program{} allows
for navigation back and forth through the board states of a match and for new
variants to be created from each of these board states. Therefore, a match is
represented as a tree of moves. The state of the game must also be present so
liberties, captures and legality of moves can be addressed, so it is represented
with its own class, which holds a reference both to the game tree and the
current move. This classes and their relationship can be seen in
\fref{fig:gameRepresentation}.

\begin{figure}[h]
	\begin{center}
		\includegraphics[width=0.7\textwidth]{diagrams/gameRepresentation.png}
		\caption{A game is represented as a tree of moves.}\label{fig:gameRepresentation}
	\end{center}
\end{figure}

\subsection{SGF}

To parse SGF files a lexer and parser have been implemented using PLY.\@ The
result of the parsing is an AST (Annotated Syntax Tree) reflecting the contents
of the text input, each node with zero or more properties, and with the ability
to convert themselves and their corresponding subtree into a GameTree. This is
done for the root node, since from the SGF specification there are some
properties only usable in the root node, like those which specify general game
information and properties such as rank of players or komi. These components are
shown in \fref{fig:sgfModule}.

\begin{figure}[h]
	\begin{center}
		\includegraphics[width=\textwidth]{diagrams/sgfModule.png}
		\caption{Components of the SGF file parsing module.}\label{fig:sgfModule}
	\end{center}
\end{figure}