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\part{Type system}
An Elna program consists of one or more source files, called \textbf{modules}.
Each module can declare \textbf{types}, \textbf{global variables} and
\textbf{procedures}, used by this module or exported to be used by other
modules.
\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]
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]
var
array: [3]Int := [1, 2, 3];
begin
array[1] := array[2]
end.
\end{lstlisting}
\chapter{Procedure types}
\begin{grammar}
<identifiers> = <identifier> \{`,' <identifier>\}.
<parameter> = <identifiers> `:\@' <type>.
<procedure-heading> = `(' [<parameter> \{`;' <parameter>\}] `)' <return-declaration>.
<procedure-body> = <constant-part> <variable-part> <statement-part> `end'.
<procedure-declaration> = `proc' <identifier-definition> <procedure-heading> \\
(<procedure-body> | `extern').
<return-declaration> = [`:\@' `!\@' | `:\@' type].
<procedure-type> = `proc' <procedure-heading>.
\end{grammar}
\begin{lstlisting}[caption=Example]
var
a: proc(Int) -> Int;
proc f(x: Int) -> Int;
end;
begin
a := f;
a(0)
end.
\end{lstlisting}
\chapter{Records}
\begin{grammar}
<field> = <identifiers> `:\@' <type>.
<record-type> = `record' [`(' <identifier> `)'] [<field> \{`;' <field>\}] `end'.
\end{grammar}
\begin{lstlisting}[caption=Example]
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> = `(' <identifiers> `)'.
\end{grammar}
\begin{lstlisting}[caption=Example]
type
E = (one, two, three);
var
e: E;
begin
e := E.one
end.
\end{lstlisting}
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