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<title>Bison 3.0.4: Grammar in Bison</title>

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<body lang="en">
<a name="Grammar-in-Bison"></a>
<div class="header">
<p>
Next: <a href="Semantic-Values.html#Semantic-Values" accesskey="n" rel="next">Semantic Values</a>, Previous: <a href="Language-and-Grammar.html#Language-and-Grammar" accesskey="p" rel="prev">Language and Grammar</a>, Up: <a href="Concepts.html#Concepts" accesskey="u" rel="up">Concepts</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Terms.html#Index-of-Terms" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="From-Formal-Rules-to-Bison-Input"></a>
<h3 class="section">1.2 From Formal Rules to Bison Input</h3>
<a name="index-Bison-grammar"></a>
<a name="index-grammar_002c-Bison"></a>
<a name="index-formal-grammar"></a>

<p>A formal grammar is a mathematical construct.  To define the language
for Bison, you must write a file expressing the grammar in Bison syntax:
a <em>Bison grammar</em> file.  See <a href="Grammar-File.html#Grammar-File">Bison Grammar Files</a>.
</p>
<p>A nonterminal symbol in the formal grammar is represented in Bison input
as an identifier, like an identifier in C.  By convention, it should be
in lower case, such as <code>expr</code>, <code>stmt</code> or <code>declaration</code>.
</p>
<p>The Bison representation for a terminal symbol is also called a <em>token
type</em>.  Token types as well can be represented as C-like identifiers.  By
convention, these identifiers should be upper case to distinguish them from
nonterminals: for example, <code>INTEGER</code>, <code>IDENTIFIER</code>, <code>IF</code> or
<code>RETURN</code>.  A terminal symbol that stands for a particular keyword in
the language should be named after that keyword converted to upper case.
The terminal symbol <code>error</code> is reserved for error recovery.
See <a href="Symbols.html#Symbols">Symbols</a>.
</p>
<p>A terminal symbol can also be represented as a character literal, just like
a C character constant.  You should do this whenever a token is just a
single character (parenthesis, plus-sign, etc.): use that same character in
a literal as the terminal symbol for that token.
</p>
<p>A third way to represent a terminal symbol is with a C string constant
containing several characters.  See <a href="Symbols.html#Symbols">Symbols</a>, for more information.
</p>
<p>The grammar rules also have an expression in Bison syntax.  For example,
here is the Bison rule for a C <code>return</code> statement.  The semicolon in
quotes is a literal character token, representing part of the C syntax for
the statement; the naked semicolon, and the colon, are Bison punctuation
used in every rule.
</p>
<div class="example">
<pre class="example">stmt: RETURN expr ';' ;
</pre></div>

<p>See <a href="Rules.html#Rules">Syntax of Grammar Rules</a>.
</p>
<hr>
<div class="header">
<p>
Next: <a href="Semantic-Values.html#Semantic-Values" accesskey="n" rel="next">Semantic Values</a>, Previous: <a href="Language-and-Grammar.html#Language-and-Grammar" accesskey="p" rel="prev">Language and Grammar</a>, Up: <a href="Concepts.html#Concepts" accesskey="u" rel="up">Concepts</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Terms.html#Index-of-Terms" title="Index" rel="index">Index</a>]</p>
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