<?xml version="1.0" encoding="utf-8" ?> <!-- for emacs: -*- coding: utf-8 -*- -->
<!-- Apache may like this line in the file .htaccess: AddCharset utf-8 .html -->
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1 plus MathML 2.0 plus SVG 1.1//EN" "http://www.w3.org/2002/04/xhtml-math-svg/xhtml-math-svg-flat.dtd" >
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head><title>optionalSignParser -- a parser that accepts an optional plus sign or minus sign</title>
<link rel="stylesheet" type="text/css" href="../../../../Macaulay2/Style/doc.css"/>
</head>
<body>
<table class="buttons">
<tr>
<td><div><a href="___N__N__Parser.html">next</a> | <a href="_const__Parser.html">previous</a> | <a href="___N__N__Parser.html">forward</a> | <a href="_const__Parser.html">backward</a> | <a href="___Parser.html">up</a> | <a href="index.html">top</a> | <a href="master.html">index</a> | <a href="toc.html">toc</a> | <a href="http://www.math.uiuc.edu/Macaulay2/">Macaulay2 web site</a></div>
</td>
</tr>
</table>
<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> > <a href="_optional__Sign__Parser.html" title="a parser that accepts an optional plus sign or minus sign">optionalSignParser</a></div>
<hr/>
<div><h1>optionalSignParser -- a parser that accepts an optional plus sign or minus sign</h1>
<div class="single"><h2>Description</h2>
<div><p>The return value is either <tt>1</tt> or <tt>-1</tt>, depending on the indicated sign.</p>
<table class="examples"><tr><td><pre>i1 : (optionalSignParser @ constParser "abc" : charAnalyzer) "abc"
o1 = (1, abc)
o1 : Sequence</pre>
</td></tr>
<tr><td><pre>i2 : (optionalSignParser @ constParser "abc" : charAnalyzer) "+abc"
o2 = (1, abc)
o2 : Sequence</pre>
</td></tr>
<tr><td><pre>i3 : (optionalSignParser @ constParser "abc" : charAnalyzer) "-abc"
o3 = (-1, abc)
o3 : Sequence</pre>
</td></tr>
</table>
</div>
</div>
<div class="single"><h2>See also</h2>
<ul><li><span><a href="_and__P.html" title="parser conjunction">Parser @ Parser</a> -- parser conjunction</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="_char__Analyzer.html" title="a lexical analyzer that provides characters from a string one at a time">charAnalyzer</a> -- a lexical analyzer that provides characters from a string one at a time</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>
</div>
<div class="waystouse"><div class="single"><h2>Code</h2>
<pre>../Parsing.m2:155:31-155:135: --source code:
optionalSignParser = Parser(c -> if c === null then 1 else if c === "-" then terminalParser(-1) else if c === "+" then terminalParser 1)</pre>
</div>
</div>
</div>
</body>
</html>
