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<div><a href="index.html" title="a framework for building parsers">Parsing</a> > <a href="___Parser.html" title="the class of all parsers">Parser</a></div>
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<div><h1>Parser -- the class of all parsers</h1>
<div class="single"><h2>Description</h2>
<div><p>A parser is a type of function that parses a sequence of tokens. Tokens can be anything except <a href="../../Macaulay2Doc/html/_null.html" title="the unique member of the empty class">null</a>. A parser <tt>p</tt> is called repeatedly, like this: <tt>p t</tt>, one token at a time. The return value that indicates acceptance of the input token is a new parser, which replaces the old, and is ready to accept the next token; the original parser <tt>p</tt> should not change its internal state. The return value that indicates rejection of the input token is <a href="../../Macaulay2Doc/html/_null.html" title="the unique member of the empty class">null</a>. Rejection may be interpreted as a syntax error.</p>
<p>When the input stream is exhausted, we call <tt>p</tt> one more time like this: <tt>p null</tt>. The return value is <a href="../../Macaulay2Doc/html/_null.html" title="the unique member of the empty class">null</a> if the parser is not in a terminal state. Otherwise the return value is the parsed (and possibly evaluated) result.</p>
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<div class="waystouse"><h2>Methods that use a parser :</h2>
<ul><li><span><a href="__st_sp__Parser.html" title="repetition of a parser">* Parser</a> -- repetition of a parser</span></li>
<li><span><a href="__pl_sp__Parser.html" title="repetition of a parser at least once">+ Parser</a> -- repetition of a parser at least once</span></li>
<li><span>Parser @ Parser, see <span><a href="_and__P.html" title="parser conjunction">andP</a> -- parser conjunction</span></span></li>
<li><span>Parser @ String, see <span><a href="_and__P.html" title="parser conjunction">andP</a> -- parser conjunction</span></span></li>
<li><span>String @ Parser, see <span><a href="_and__P.html" title="parser conjunction">andP</a> -- parser conjunction</span></span></li>
<li><span><a href="___Function_sp_pc_sp__Parser.html" title="transform the value returned by a parser">Function % Parser</a> -- transform the value returned by a parser</span></li>
<li><span>Parser | Parser, see <span><a href="_or__P.html" title="parsing alternatives">orP</a> -- parsing alternatives</span></span></li>
<li><span>Parser | String, see <span><a href="_or__P.html" title="parsing alternatives">orP</a> -- parsing alternatives</span></span></li>
<li><span>String | Parser, see <span><a href="_or__P.html" title="parsing alternatives">orP</a> -- parsing alternatives</span></span></li>
<li><span><a href="___Parser_sp_co_sp__Analyzer.html" title="combine a parser with a lexical analyzer to make a complete system">Parser : Analyzer</a> -- combine a parser with a lexical analyzer to make a complete system</span></li>
</ul>
<h2>Fixed objects of class Parser :</h2>
<ul><li><span><a href="_dead__Parser.html" title="a parser which accepts no tokens and is not in a terminal state">deadParser</a> -- a parser which accepts no tokens and is not in a terminal state</span></li>
<li><span><a href="_letter__Parser.html" title="a parser that accepts a single letter and returns it">letterParser</a> -- a parser that accepts a single letter and returns it</span></li>
<li><span><a href="___N__N__Parser.html" title="a parser that accepts (and returns) a natural number, one character at a time">NNParser</a> -- a parser that accepts (and returns) a natural number, one character at a time</span></li>
<li><span><a href="_null__Parser.html" title="a terminal parser that returns the value nil">nullParser</a> -- a terminal parser that returns the value nil</span></li>
<li><span><a href="_optional__Sign__Parser.html" title="a parser that accepts an optional plus sign or minus sign">optionalSignParser</a> -- a parser that accepts an optional plus sign or minus sign</span></li>
<li><span><a href="___Q__Q__Parser.html" title="a parser that accepts (and returns) a rational number, one character at a time">QQParser</a> -- a parser that accepts (and returns) a rational number, one character at a time</span></li>
<li><span><a href="___Z__Z__Parser.html" title="a parser that accepts (and returns) an integer, one character at a time">ZZParser</a> -- a parser that accepts (and returns) an integer, one character at a time</span></li>
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<div class="waystouse"><h2>For the programmer</h2>
<p>The object <a href="___Parser.html" title="the class of all parsers">Parser</a> is <span>a <a href="../../Macaulay2Doc/html/___Self__Initializing__Type.html">self initializing type</a></span>, with ancestor classes <a href="../../Macaulay2Doc/html/___Function__Closure.html" title="the class of all function closures">FunctionClosure</a> < <a href="../../Macaulay2Doc/html/___Function.html" title="the class of all functions">Function</a> < <a href="../../Macaulay2Doc/html/___Thing.html" title="the class of all things">Thing</a>.</p>
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<div><h3>Menu</h3>
<h4>simple parsers</h4>
<ul><li><span><a href="_dead__Parser.html" title="a parser which accepts no tokens and is not in a terminal state">deadParser</a> -- a parser which accepts no tokens and is not in a terminal state</span></li>
<li><span><a href="_terminal__Parser.html" title="produce a parser in a terminal state">terminalParser</a> -- produce a parser in a terminal state</span></li>
<li><span><a href="_null__Parser.html" title="a terminal parser that returns the value nil">nullParser</a> -- a terminal parser that returns the value nil</span></li>
<li><span><a href="_future__Parser.html" title="forward reference to a parser not defined yet">futureParser</a> -- forward reference to a parser not defined yet</span></li>
<li><span><a href="_letter__Parser.html" title="a parser that accepts a single letter and returns it">letterParser</a> -- a parser that accepts a single letter and returns it</span></li>
<li><span><a href="_const__Parser.html" title="produce a parser that accepts a fixed string, one character at a time">constParser</a> -- produce a parser that accepts a fixed string, one character at a time</span></li>
<li><span><a href="_optional__Sign__Parser.html" title="a parser that accepts an optional plus sign or minus sign">optionalSignParser</a> -- a parser that accepts an optional plus sign or minus sign</span></li>
<li><span><a href="___N__N__Parser.html" title="a parser that accepts (and returns) a natural number, one character at a time">NNParser</a> -- a parser that accepts (and returns) a natural number, one character at a time</span></li>
<li><span><a href="___Z__Z__Parser.html" title="a parser that accepts (and returns) an integer, one character at a time">ZZParser</a> -- a parser that accepts (and returns) an integer, one character at a time</span></li>
<li><span><a href="___Q__Q__Parser.html" title="a parser that accepts (and returns) a rational number, one character at a time">QQParser</a> -- a parser that accepts (and returns) a rational number, one character at a time</span></li>
</ul>
<h4>making new parsers from old ones</h4>
<ul><li><span><a href="_opt__P.html" title="making a parser optional">optP</a> -- making a parser optional</span></li>
<li><span><a href="_or__P.html" title="parsing alternatives">orP</a> -- parsing alternatives</span></li>
<li><span><a href="_and__P.html" title="parser conjunction">andP</a> -- parser conjunction</span></li>
<li><span><a href="__st_sp__Parser.html" title="repetition of a parser">* Parser</a> -- repetition of a parser</span></li>
<li><span><a href="__pl_sp__Parser.html" title="repetition of a parser at least once">+ Parser</a> -- repetition of a parser at least once</span></li>
<li><span><a href="___Function_sp_pc_sp__Parser.html" title="transform the value returned by a parser">Function % Parser</a> -- transform the value returned by a parser</span></li>
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