\documentclass{scrreprt}

\usepackage[T1]{fontenc}
\usepackage{tabularx}
\usepackage{booktabs}
\usepackage{listings}
\usepackage{syntax}

\title{The programming language Elna}

\begin{document}

\maketitle
\tableofcontents

\chapter{Introduction}

Elna is a simple, imperative, low-level programming language.

It is intendet to accompany other languages in the areas, where a high-level
language doesn't fit well. It is also supposed to be an intermediate
representation for a such high-level hypothetical programming language.

\part{Language}

\chapter{Expressions}

The expression \verb|@r.field| includes 3 expressions:

\begin{enumerate}
	\item Variable expression \verb|r|.
	\item Field access \verb|(r).field|.
	\item Address taking \verb|@(r.field)|.
\end{enumerate}

The expression is evaluated in the above order. The postfix expressions
like field access have higher precedence than prefix operators.

\section{Binary expressions}

\begin{table}
\centering
\begin{tabularx}{0.8\textwidth}{%
	l
	>{\centering\arraybackslash}X
	>{\raggedright\arraybackslash}X
}
	\textbf{Precedence} & \textbf{Operator} & \textbf{Description}\\
	\toprule
	1 & $* \quad / \quad \%$ & Multiplication, division and remainder.\\
	\midrule
	2 & $+ \quad -$ & Addition and subtraction.\\
	\midrule
	3 & $<< \quad >>$ & Left and right shifts.\\
	\midrule
	4 & $= \quad <> \quad > \quad < \quad <= \quad >=$ & Relational operators.\\
	\midrule
	5 & $or \quad xor \quad \&$ & Logical operators.\\
	\bottomrule
\end{tabularx}
\caption{Operator precedence}
\end{table}

\section{Unary expressions}

Unary expressions are expressions with a prefix operator followed by one
operand.

\verb|@| (\textit{at sign}) takes the address of its operand. The operand expression should be
addressable.

\verb|-| (\textit{minus}) negates a numeric value.

\verb|~| (\textit{tilde}) applied on a boolean acts as logical not. Applied on a numeric – as
bitwise not.

\chapter{Conditional statements}
\chapter{Loop statements}

\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}

\chapter{Type operations}

\chapter{Cast}

\begin{grammar}
<cast> = `cast' `(' <expression> `:\@' <type> `)'.
\end{grammar}

The type of an object can be reinterpreted with a cast expression: \\
\verb|cast(object: Type)|.

\chapter{Traits}

\begin{grammar}
<trait-identifier> = `#' <identifier>.

<trait> = <trait-identifier> `(' [<types>] `)'.
\end{grammar}

Traits allow to query some information about the types, like their size or
field offset or alignment. Calling a trait looks like a procedure call but
traits names start with a \verb|#| and their arguments are type expressions and
not value expressions.

Supported compiler traits:

\begin{itemize}
	\item \verb|#size(T)| queries type size.
	\item \verb|#align(T)| queries type alignment.
	\item \verb|#offset(T, F)| queries the offset of the field \verb|F| in the record \verb|T|.
\end{itemize}

\part{Appendix}

\chapter{Syntax}

\begin{grammar}
<letter> = `A' | `B' | … | `Z' | `a' | `b' | … | `z' | `\_'.

<counting-digit> = `1' | `2' | `3' | `4' | `5' | `6' | `7' | `8' | `9'.

<decimal-digit> = `0' | <counting-digit>.

<hex-digit> = <decimal-digit> | `A' | `B' | … | `F' | `a' | `b' | … | `f'.

<binary-digit> = `0' | `1'.

<hex-character> = `\\x' <hex-digit> <hex-digit>.

<escaped-character> = `\\' \\
	(`n' | `a' | `b' | `t' | `f' | `r' | `v' | `\\' | `\textquotesingle' | `\textquotedbl' | `?\@' | `0').

<printable-character> = \enspace? a printable ASCII character\space?.

<character> = <printable-character> | <escaped-character> | <hex-digit>.

<identifier> = <letter> \{<letter> | <decimal-digit>\}.

<identifier-definition> = <identifier> [`*'].

<trait-identifier> = `#' <identifier>.

<integer-literal> = `0' | <counting-digit> \{<decimal-digit>\}.

<word-literal> = <integer-literal> `u'
	\alt{} `0' (`X' | `x') <hex-digit> \{<hex-digit>\}
	\alt{} `0' (`B' | `b') <binary-digit> \{<binary-digit>\}.

<real-literal> = <integer-literal> `.\@' <decimal-digit> \{<decimal-digit>\}
	\alt{} <integer-literal>\} `e' [`+' | `-'] <decimal-digit> \{<decimal-digit>\}.

<string-literal> = `\textquotedbl' \{<character>\} `\textquotedbl'.

<character-literal> = `\textquotesingle' <character> `\textquotesingle'.

<literal> = <integer-literal> | <word-literal> | <real-literal>
	\alt{} <string-literal> | <character-literal>
	\alt{} `true' | `false' | `nil'.

<trait> = <trait-identifier> `(' [<types>] `)'.

<cast> = `cast' `(' <expression> `:\@' <type> `)'.

<procedure-call> = <designator> `(' [<expressions>] `)'.

<relation-operator> = `=' | `<>' | `<' | `>' | `<=' | `>='.

<multiplication-operator> = `*' | `/' | `\%'.

<addition-operator> = `+' | `-'.

<shift-operator> = `<<' | `>>'.

<unary-operator> = `@' | `~' | `-'.

<selector> = `[' <expression> `]' | `.\@' <identifier> | `^'.

<case> = <expressions> `:\@' <optional-statements>.

<designator> = <reference> <selector> | <identifier>.

<reference> = <literal>
	\alt{} <designator>
	\alt{} <trait>
	\alt{} <cast>
	\alt{} <procedure-call>
	\alt{} `(' <expression> `)'.

<factor> = <unary-operator> <factor> | <reference>.

<term> = <factor> \{<multiplication-operator> <factor>\}.

<simple-expression> = <term> \{<addition-operator> <term>\}.

<comparand> = <simple-expression> \{<shift-operator> <simple-expression>\}.

<relation> = <comparand> \{<relation-operator> <comparand>\}.

<operand> = <relation> \{`&' <relation>\}.

<expression> = <operand> \{(`or' | `xor') <operand>\}.

<expressions> = <expression> \{`,' <expression>\}.

<identifier-definitions> = <identifier-definition> \{`,' <identifier-definition>\}.

<types> = <type> \{`,' <type>\}.

<required-statements> = <statement> \{`;' <statement>\}.

<optional-statements> = [<required-statements>].

<return-declaration> = [`->' `!\@' | `->' type].

<field> = <identifier> `:\@' <type>.

<array-type> = `[' <expression> `]' <type>.

<pointer-type> = `^' <type>.

<record-type> = `record' [`(' <identifier> `)'] [<field> \{`;' <field>\}] `end'.

<enumeration-type> = `(' <identifier> \{`,' <identifier>\} `)'.

<procedure-type> = `proc' `(' [<types>] `)' <return-declaration>.

<type> = <array-type>
	\alt{} <pointer-type>
	\alt{} <record-type>
	\alt{} <enumeration-type>
	\alt{} <procedure-type>
	\alt{} <identifier>.

<assignment> = <designator> `:=' <expression>.

<if-statement> = `if' <expression> `then' <optional-statements> \\
    \{`elsif' <expression> `then' <optional-statements>\} \\
	{[`else' <optional-statements>]} `end'.

<while-statement> = `while' <expression> `do' <optional-statements> \\
    \{`elsif' <expression> `do' <optional-statements>\} `end'.

<defer-statement> = `defer' <optional-statements> `end'.

<case-statement> = `case' <expression> `of' <case> \{`|' case\} \\
	{[`else' <optional-statements>]} `end'.

<label-declaration> = `.\@' <identifier>.

<goto-statement> = `goto' <identifier>.

<statement> = <assignment> | <procedure-call> | <defer-statement>
    | <label-declaration> | <goto-statement> |
    | <while-statement> | <if-statement> | <case-statement>.

<statement-part> = [`begin' <required-statements>
	\alt{} `return' <expression>
	\alt{} `begin' <required-statements> `;' `return' <expression>].

<constant-declaration> = <identifier-definition> `:=' <expression>.

<constant-part> = [`const' \{<constant-declaration> `;'\}].

<variable-declaration> = <identifier-definitions> `:\@' <type> \\
	{[`:=' (<expression> | `extern')]}.

<variable-part> = [`var' \{<variable-declaration> `;'\}].

<type-declaration> = <identifier-definition> `=' <type>.

<type-part> = [`type' \{<type-declaration> `;'\}].

<import-declaration> = <identifier> \{`.\@' <identifier>\}.

<import-part> = [`import' \{import-declaration `;'\}].

<procedure-heading> = `proc' <identifier-definition> \\
	`(' [<field> \{`,' <field>\}] `)' <return-declaration>.

<block> = <constant-part> <variable-part> <statement-part> `end'.

<procedure-declaration> = <procedure-heading> `;' (block | `extern').

<declaration-sequence> = <import-part> \\
    <constant-part> <type-part> <variable-part> \\
	\{<procedure-declaration> `;'\}.

<program> = `program' `;' <declaration-sequence> <statement-part> `end' `.\@'
	\alt{} `module' `;' <declaration-sequence> `end' `.\@'.
\end{grammar}

\end{document}