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POParsing percent expressions with antlr4
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  1. POParsing percent expressions with antlr4
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    copied!<p>I'm trying to parse algebraic expressions with ANTLR4. One feature I tried to accomplish with my parser is the "intelligent" handling of percent expressions. </p> <p><strong>Edit:</strong> The goal is to make the calculation of discounts or tips in a restaurant easier. E.g. if you see an advert "30% off" you could enter "price - 30%" and get the correct result. Or in a restaurant you could enter the price of your meal plus 15% and get the sum you have to pay including a tip of 15%. But this interpretation should only occur if the expression looks like "expression1 (- or +) expression2". In all other cases the percent sign should be interpreted as usual. The Google Search box calculator behaves like that.<strong>/Edit</strong></p> <p><code>100-30%</code> should return <em>70</em><br> <code>100-(20+10)%</code> should also return <em>70</em><br> <code>3+(100-(20+10)%)</code> should return <em>73</em><br> <strong>but</strong><br> <code>5%</code> should return <em>0.05</em><br> <code>(5+5)%</code> should return <em>0.10</em></p> <p>My grammar looks like this:</p> <pre><code>expr: e EOF ; e: '-'a=e | '(' a=e ')' | a=e op=(ADD|SUB) b=e '%' | a=e op=(ADD|SUB) b=e | a=e'%' //**PERCENTRULE** | FLT ; ADD : '+' ; SUB : '-' ; FLT: [0-9]+(('.'|',')[0-9]+)?; NEWLINE:'\r'? '\n' ; WS : [ \t\n]+ -&gt; skip ; </code></pre> <p>For the expression <code>100-30%</code> I would <strong>expect</strong> the this tree:<br> <img src="https://i.stack.imgur.com/ZEQCz.png" alt="Expected parse tree for the expression &quot;100-30%&quot;"> </p> <p>But I get this:<br> <img src="https://i.stack.imgur.com/RNiOl.png" alt="parse tree for the expression &quot;100-30%"><br> How can I get the correct tree (without deleting PERCENTRULE)?</p>
 

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