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<h3>Table of Contents</h3>
<ul class="link-list" role="directory">
<li><a href="#label-Racc+Grammar+File+Reference">Racc Grammar File Reference</a>
<li><a href="#label-Global+Structure">Global Structure</a>
<li><a href="#label-Class+Block+and+User+Code+Block">Class Block and User Code Block</a>
<li><a href="#label-Comments">Comments</a>
<li><a href="#label-Class+Block">Class Block</a>
<li><a href="#label-Grammar+Block">Grammar Block</a>
<li><a href="#label-Operator+Precedence">Operator Precedence</a>
<li><a href="#label-expect">expect</a>
<li><a href="#label-Declaring+Tokens">Declaring Tokens</a>
<li><a href="#label-Options">Options</a>
<li><a href="#label-Converting+Token+Symbol">Converting Token Symbol</a>
<li><a href="#label-Start+Rule">Start Rule</a>
<li><a href="#label-User+Code+Block">User Code Block</a>
</ul>
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<li><a href="../../../lib/racc/rdoc/grammar_en_rdoc.html">grammar.en</a>
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<h1 id="label-Racc+Grammar+File+Reference"><a href="../../../Racc.html"><code>Racc</code></a> Grammar <a href="../../../File.html"><code>File</code></a> Reference<span><a href="#label-Racc+Grammar+File+Reference">¶</a> <a href="#top">↑</a></span></h1>
<h2 id="label-Global+Structure">Global Structure<span><a href="#label-Global+Structure">¶</a> <a href="#top">↑</a></span></h2>
<h2 id="label-Class+Block+and+User+Code+Block"><a href="../../../Class.html"><code>Class</code></a> Block and User Code Block<span><a href="#label-Class+Block+and+User+Code+Block">¶</a> <a href="#top">↑</a></span></h2>
<p>There are two blocks on the toplevel. One is the 'class' block, the other is the 'user code' block. The 'user code' block MUST be placed after the 'class' block.</p>
<h2 id="label-Comments">Comments<span><a href="#label-Comments">¶</a> <a href="#top">↑</a></span></h2>
<p>You can insert comments about all places. Two styles of comments can be used, Ruby style '#.….' and C style '/*.…..*/'.</p>
<h2 id="label-Class+Block"><a href="../../../Class.html"><code>Class</code></a> Block<span><a href="#label-Class+Block">¶</a> <a href="#top">↑</a></span></h2>
<p>The class block is formed like this:</p>
<pre>class CLASS_NAME
[precedence table]
[token declarations]
[expected number of S/R conflicts]
[options]
[semantic value conversion]
[start rule]
rule
GRAMMARS</pre>
<p>CLASS_NAME is a name of the parser class. This is the name of the generating parser class.</p>
<p>If CLASS_NAME includes '::', <a href="../../../Racc.html"><code>Racc</code></a> outputs the module clause. For example, writing “class M::C” causes the code below to be created:</p>
<pre>module M
class C
:
:
end
end</pre>
<h2 id="label-Grammar+Block">Grammar Block<span><a href="#label-Grammar+Block">¶</a> <a href="#top">↑</a></span></h2>
<p>The grammar block describes grammar which is able to be understood by the parser. Syntax is:</p>
<pre>(token): (token) (token) (token).... (action)
(token): (token) (token) (token).... (action)
| (token) (token) (token).... (action)
| (token) (token) (token).... (action)</pre>
<p>(action) is an action which is executed when its (token)s are found. (action) is a ruby code block, which is surrounded by braces:</p>
<pre>{ print val[0]
puts val[1] }</pre>
<p>Note that you cannot use '%' string, here document, '%r' regexp in action.</p>
<p>Actions can be omitted. When it is omitted, '' (empty string) is used.</p>
<p>A return value of action is a value of the left side value ($$). It is the value of the result, or the returned value by `return` statement.</p>
<p>Here is an example of the whole grammar block.</p>
<pre>rule
goal: definition rules source { result = val }
definition: /* none */ { result = [] }
| definition startdesig { result[0] = val[1] }
| definition
precrule # this line continues from upper line
{
result[1] = val[1]
}
startdesig: START TOKEN</pre>
<p>You can use the following special local variables in action:</p>
<ul><li>
<p>result ($$)</p>
</li></ul>
<p>The value of the left-hand side (lhs). A default value is <a href="0">val</a>.</p>
<ul><li>
<p>val ($1,$2,$3…)</p>
</li></ul>
<p>An array of value of the right-hand side (rhs).</p>
<ul><li>
<p>_values (…$-2,$-1,$0)</p>
</li></ul>
<p>A stack of values. DO NOT MODIFY this stack unless you know what you are doing.</p>
<h2 id="label-Operator+Precedence">Operator Precedence<span><a href="#label-Operator+Precedence">¶</a> <a href="#top">↑</a></span></h2>
<p>This function is equal to '%prec' in yacc. To designate this block:</p>
<pre class="ruby"><span class="ruby-identifier">prechigh</span>
<span class="ruby-identifier">nonassoc</span> <span class="ruby-string">'++'</span>
<span class="ruby-identifier">left</span> <span class="ruby-string">'*'</span> <span class="ruby-string">'/'</span>
<span class="ruby-identifier">left</span> <span class="ruby-string">'+'</span> <span class="ruby-string">'-'</span>
<span class="ruby-identifier">right</span> <span class="ruby-string">'='</span>
<span class="ruby-identifier">preclow</span>
</pre>
<p>`right` is yacc's %right, `left` is yacc's %left.</p>
<p>`=` + (symbol) means yacc's %prec:</p>
<pre>prechigh
nonassoc UMINUS
left '*' '/'
left '+' '-'
preclow
rule
exp: exp '*' exp
| exp '-' exp
| '-' exp =UMINUS # equals to "%prec UMINUS"
:
:</pre>
<h2 id="label-expect">expect<span><a href="#label-expect">¶</a> <a href="#top">↑</a></span></h2>
<p><a href="../../../Racc.html"><code>Racc</code></a> has bison's “expect” directive.</p>
<pre># Example
class MyParser
rule
expect 3
:
:</pre>
<p>This directive declares “expected” number of shift/reduce conflicts. If “expected” number is equal to real number of conflicts, <a href="../../../Racc.html"><code>Racc</code></a> does not print conflict warning message.</p>
<h2 id="label-Declaring+Tokens">Declaring Tokens<span><a href="#label-Declaring+Tokens">¶</a> <a href="#top">↑</a></span></h2>
<p>By declaring tokens, you can avoid many meaningless bugs. If declared token does not exist or existing token does not decleared, <a href="../../../Racc.html"><code>Racc</code></a> output warnings. Declaration syntax is:</p>
<pre class="ruby"><span class="ruby-identifier">token</span> <span class="ruby-constant">TOKEN_NAME</span> <span class="ruby-constant">AND_IS_THIS</span>
<span class="ruby-constant">ALSO_THIS_IS</span> <span class="ruby-constant">AGAIN_AND_AGAIN</span> <span class="ruby-constant">THIS_IS_LAST</span>
</pre>
<h2 id="label-Options">Options<span><a href="#label-Options">¶</a> <a href="#top">↑</a></span></h2>
<p>You can write options for <a href="../../../Racc.html"><code>Racc</code></a> command in your <a href="../../../Racc.html"><code>Racc</code></a> file.</p>
<pre class="ruby"><span class="ruby-identifier">options</span> <span class="ruby-constant">OPTION</span> <span class="ruby-constant">OPTION</span> <span class="ruby-operator">...</span>
</pre>
<p>Options are:</p>
<ul><li>
<p>omit_action_call</p>
</li></ul>
<p>omits empty action call or not.</p>
<ul><li>
<p>result_var</p>
</li></ul>
<p>uses local variable “result” or not.</p>
<p>You can use 'no_' prefix to invert their meanings.</p>
<h2 id="label-Converting+Token+Symbol">Converting Token <a href="../../../Symbol.html"><code>Symbol</code></a><span><a href="#label-Converting+Token+Symbol">¶</a> <a href="#top">↑</a></span></h2>
<p>Token symbols are, as default,</p>
<pre>* naked token string in Racc file (TOK, XFILE, this_is_token, ...)
--> symbol (:TOK, :XFILE, :this_is_token, ...)
* quoted string (':', '.', '(', ...)
--> same string (':', '.', '(', ...)</pre>
<p>You can change this default by “convert” block. Here is an example:</p>
<pre>convert
PLUS 'PlusClass' # We use PlusClass for symbol of `PLUS'
MIN 'MinusClass' # We use MinusClass for symbol of `MIN'
end</pre>
<p>We can use almost all ruby value can be used by token symbol, except 'false' and 'nil'. These cause unexpected parse error.</p>
<p>If you want to use <a href="../../../String.html"><code>String</code></a> as token symbol, special care is required. For example:</p>
<pre>convert
class '"cls"' # in code, "cls"
PLUS '"plus\n"' # in code, "plus\n"
MIN "\"minus#{val}\"" # in code, \"minus#{val}\"
end</pre>
<h2 id="label-Start+Rule">Start Rule<span><a href="#label-Start+Rule">¶</a> <a href="#top">↑</a></span></h2>
<p>'%start' in yacc. This changes start rule.</p>
<pre class="ruby"><span class="ruby-identifier">start</span> <span class="ruby-identifier">real_target</span>
</pre>
<h2 id="label-User+Code+Block">User Code Block<span><a href="#label-User+Code+Block">¶</a> <a href="#top">↑</a></span></h2>
<p>“User Code Block” is a Ruby source code which is copied to output. There are three user code blocks, “header” “inner” and “footer”.</p>
<p>Format of user code is like this:</p>
<pre>---- header
ruby statement
ruby statement
ruby statement
---- inner
ruby statement
:
:</pre>
<p>If four '-' exist on the line head, <a href="../../../Racc.html"><code>Racc</code></a> treats it as the beginning of the user code block. The name of the user code block must be one word.</p>
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