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<title>Bison 3.0.4: Rpcalc Rules</title>

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<a name="Rpcalc-Rules"></a>
<div class="header">
<p>
Next: <a href="Rpcalc-Lexer.html#Rpcalc-Lexer" accesskey="n" rel="next">Rpcalc Lexer</a>, Previous: <a href="Rpcalc-Declarations.html#Rpcalc-Declarations" accesskey="p" rel="prev">Rpcalc Declarations</a>, Up: <a href="RPN-Calc.html#RPN-Calc" accesskey="u" rel="up">RPN Calc</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="Grammar-Rules-for-rpcalc"></a>
<h4 class="subsection">2.1.2 Grammar Rules for <code>rpcalc</code></h4>

<p>Here are the grammar rules for the reverse polish notation calculator.
</p>
<div class="example">
<pre class="example">input:
  %empty
| input line
;
</pre><pre class="example">
</pre><pre class="example">line:
  '\n'
| exp '\n'      { printf (&quot;%.10g\n&quot;, $1); }
;
</pre><pre class="example">
</pre><pre class="example">exp:
  NUM           { $$ = $1;           }
| exp exp '+'   { $$ = $1 + $2;      }
| exp exp '-'   { $$ = $1 - $2;      }
| exp exp '*'   { $$ = $1 * $2;      }
| exp exp '/'   { $$ = $1 / $2;      }
| exp exp '^'   { $$ = pow ($1, $2); }  /* Exponentiation */
| exp 'n'       { $$ = -$1;          }  /* Unary minus    */
;
</pre><pre class="example">%%
</pre></div>

<p>The groupings of the rpcalc &ldquo;language&rdquo; defined here are the expression
(given the name <code>exp</code>), the line of input (<code>line</code>), and the
complete input transcript (<code>input</code>).  Each of these nonterminal
symbols has several alternate rules, joined by the vertical bar &lsquo;<samp>|</samp>&rsquo;
which is read as &ldquo;or&rdquo;.  The following sections explain what these rules
mean.
</p>
<p>The semantics of the language is determined by the actions taken when a
grouping is recognized.  The actions are the C code that appears inside
braces.  See <a href="Actions.html#Actions">Actions</a>.
</p>
<p>You must specify these actions in C, but Bison provides the means for
passing semantic values between the rules.  In each action, the
pseudo-variable <code>$$</code> stands for the semantic value for the grouping
that the rule is going to construct.  Assigning a value to <code>$$</code> is the
main job of most actions.  The semantic values of the components of the
rule are referred to as <code>$1</code>, <code>$2</code>, and so on.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="Rpcalc-Input.html#Rpcalc-Input" accesskey="1">Rpcalc Input</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Explanation of the <code>input</code> nonterminal
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Rpcalc-Line.html#Rpcalc-Line" accesskey="2">Rpcalc Line</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Explanation of the <code>line</code> nonterminal
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Rpcalc-Expr.html#Rpcalc-Expr" accesskey="3">Rpcalc Expr</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Explanation of the <code>expr</code> nonterminal
</td></tr>
</table>

<hr>
<div class="header">
<p>
Next: <a href="Rpcalc-Lexer.html#Rpcalc-Lexer" accesskey="n" rel="next">Rpcalc Lexer</a>, Previous: <a href="Rpcalc-Declarations.html#Rpcalc-Declarations" accesskey="p" rel="prev">Rpcalc Declarations</a>, Up: <a href="RPN-Calc.html#RPN-Calc" accesskey="u" rel="up">RPN Calc</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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