扩展简单的ANTLR语法以支持输入变量 [英] Extending simple ANTLR grammer to support input variables

问题描述

我还在我寻求一种非常简单的语言，我现在知道没有。所以我自己用ANTLR3写一个。

I'm still on my quest for a really simple language and I know now that there are none. So I'm writing one myself using ANTLR3.

我在这个答案：

Exp.g：

grammar Exp;

eval returns [double value]
    :    exp=additionExp {$value = $exp.value;}
    ;

additionExp returns [double value]
    :    m1=multiplyExp       {$value =  $m1.value;} 
         ( '+' m2=multiplyExp {$value += $m2.value;} 
         | '-' m2=multiplyExp {$value -= $m2.value;}
         )* 
    ;

multiplyExp returns [double value]
    :    a1=atomExp       {$value =  $a1.value;}
         ( '*' a2=atomExp {$value *= $a2.value;} 
         | '/' a2=atomExp {$value /= $a2.value;}
         )* 
    ;

atomExp returns [double value]
    :    n=Number                {$value = Double.parseDouble($n.text);}
    |    '(' exp=additionExp ')' {$value = $exp.value;}
    ;

Number
    :    ('0'..'9')+ ('.' ('0'..'9')+)?
    ;

WS  
    :   (' ' | '\t' | '\r'| '\n') {$channel=HIDDEN;}
    ;

Java代码：

public Double evaluate(String string, Map<String, Double> input) throws RecognitionException {
    ANTLRStringStream in = new ANTLRStringStream(string);
    ExpLexer lexer = new ExpLexer(in);
    CommonTokenStream tokens = new CommonTokenStream(lexer);
    return new ExpParser(tokens).eval();
}

使用这个ANTLR语法我可以计算像

Using this ANTLR grammer I can evaluate expressions like

(12+14)/2

并得到13作为结果。

现在我的用例中唯一缺少的是一种将简单的双变量注入其中的方法，这样我就可以通过提供{A：12.0，B：14.0}作为输入地图来评估以下内容：

Now the only thing missing for my use-case is a way to inject simple double variables into this, so that I can evaluate the following by supplying {"A": 12.0, "B":14.0} as the input map:

(A+B)/2

任何想法？

推荐答案

你可以创建一个 Map< String，Double>解析器中的内存并在语法中引入标识符：

You could create a Map<String, Double> memory in your parser and introduce a Identifier in your grammar:

Identifier
  :  ('a'..'z' | 'A'..'Z' | '_') ('a'..'z' | 'A'..'Z' | '_' | '0'..'9')*
  ;

然后你的 atomExp 解析器规则看起来像这个：

Then your atomExp parser rule would look like this:

atomExp returns [double value]
    :    n=Number                {$value = Double.parseDouble($n.text);}
    |    i=Identifier            {$value = memory.get($i.text);} // <- added!
    |    '(' exp=additionExp ')' {$value = $exp.value;}
    ;

这是一个小型（完整）演示：

Here's a small (complete) demo:

grammar Exp;

@parser::members {

  private java.util.HashMap<String, Double> memory = new java.util.HashMap<String, Double>();

  public static Double eval(String expression) throws Exception {
    return eval(expression, new java.util.HashMap<String, Double>()); 
  }

  public static Double eval(String expression, java.util.Map<String, Double> vars) throws Exception {
    ANTLRStringStream in = new ANTLRStringStream(expression);
    ExpLexer lexer = new ExpLexer(in);
    CommonTokenStream tokens = new CommonTokenStream(lexer);
    ExpParser parser = new ExpParser(tokens);
    parser.memory.putAll(vars);
    return parser.parse(); 
  }
}

parse returns [double value]
    :    exp=additionExp {$value = $exp.value;}
    ;

additionExp returns [double value]
    :    m1=multiplyExp      {$value =  $m1.value;} 
        ( '+' m2=multiplyExp {$value += $m2.value;} 
        | '-' m2=multiplyExp {$value -= $m2.value;}
        )*  
    ;

multiplyExp returns [double value]
    :   a1=atomExp       {$value =  $a1.value;}
        ( '*' a2=atomExp {$value *= $a2.value;} 
        | '/' a2=atomExp {$value /= $a2.value;}
        )*  
    ;

atomExp returns [double value]
    :    n=Number                {$value = Double.parseDouble($n.text);}
    |    i=Identifier            {$value = memory.get($i.text);}
    |    '(' exp=additionExp ')' {$value = $exp.value;}
    ;

Identifier
    :    ('a'..'z' | 'A'..'Z' | '_') ('a'..'z' | 'A'..'Z' | '_' | '0'..'9')*
    ;

Number
    :    ('0'..'9')+ ('.' ('0'..'9')+)?
    ;

WS  
    :   (' ' | '\t' | '\r'| '\n') {$channel=HIDDEN;}
    ;

现在没有必要自己实例化解析器/词法分析器，你可以简单地做：

And now theres no need to instantiate the parser/lexer yourself, you can simply do:

import org.antlr.runtime.*;
import java.util.*;

public class ANTLRDemo {
    public static void main(String[] args) throws Exception {
        Map<String, Double> vars = new HashMap<String, Double>();
        vars.put("two", 2.0);
        vars.put("pi", Math.PI);
        System.out.println(ExpParser.eval("two * pi", vars));
    }
}

将产生：

6.283185307179586

祝你好运！

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