Add documentation

doc/type-system.tex

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+\part{Type system}
+
+\begin{grammar}
+<type> = <array-type>
+	\alt{} <pointer-type>
+	\alt{} <record-type>
+	\alt{} <enumeration-type>
+	\alt{} <procedure-type>
+	\alt{} <identifier>.
+\end{grammar}
+
+\chapter{Primitive types}
+
+\begin{itemize}
+	\item Pointer
+	\item Word
+	\item Int
+	\item Bool
+	\item String
+	\item Char
+\end{itemize}
+
+\chapter{Pointer types}
+
+\begin{grammar}
+<pointer-type> = `^' <type>.
+\end{grammar}
+
+\begin{lstlisting}[caption=Example]
+program;
+var
+  x: Int;
+  y: ^Int;
+begin
+  y := @x;
+  y^ := 0
+end.
+\end{lstlisting}
+
+\chapter{Static array}
+
+\begin{grammar}
+<array-type> = `[' <expression> `]' <type>.
+\end{grammar}
+
+\begin{lstlisting}[caption=Example]
+program;
+var
+  array: [3]Int := [1, 2, 3];
+begin
+  array[1] := array[2]
+end.
+\end{lstlisting}
+
+\chapter{Procedure types}
+
+\begin{grammar}
+<procedure-heading> = `proc' <identifier-definition> \\
+	`(' [<field> \{`,' <field>\}] `)' <return-declaration>.
+
+<block> = <constant-part> <variable-part> <statement-part> `end'.
+
+<procedure-declaration> = <procedure-heading> `;' (block | `extern').
+
+<return-declaration> = [`->' `!\@' | `->' type].
+
+<procedure-type> = `proc' `(' [<types>] `)' <return-declaration>.
+\end{grammar}
+
+\begin{lstlisting}[caption=Example]
+program;
+var
+  a: proc(Int) -> Int;
+
+proc f(x: Int) -> Int;
+end;
+
+begin
+  a := f;
+  a(0)
+end.
+\end{lstlisting}
+
+\chapter{Records}
+
+\begin{grammar}
+<field> = <identifier> `:\@' <type>.
+
+<record-type> = `record' [`(' <identifier> `)'] [<field> \{`;' <field>\}] `end'.
+\end{grammar}
+
+\begin{lstlisting}[caption=Example]
+program;
+type
+  T = record
+    x: Int
+  end;
+  U = record(T)
+    y: Int;
+    z: Int
+  end;
+
+var
+  u: U;
+begin
+  u := U(0, 1, 2);
+  u.x := 3
+end.
+\end{lstlisting}
+
+\chapter{Enumerations}
+
+\begin{grammar}
+<enumeration-type> = `(' <identifier> \{`,' <identifier>\} `)'.
+\end{grammar}
+
+\begin{lstlisting}[caption=Example]
+program;
+type
+  E = (one, two, three);
+var
+  e: E;
+begin
+  e := E.one
+end.
+\end{lstlisting}