C#-Silverlight中的JavaScript表达式解析器

大家好！我有一个Silverlight项目,该项目需要帮助用户创建JavaScript逻辑表达式(例如“ var1！= var2&& var3> = var4”).很简单.问题是我没有太多时间自己创建一个人,因为调整过渡表会浪费一些时间.

因此,我在网上搜索一个,但是发现的只有几个类可以帮助您验证JavaScript,但是我需要一种加载,解析然后写回的方法.所以我想知道是否有人对我的做法有任何想法.我假设它不需要太多代码,也不必是C#示例.如果您能用C甚至伪代码给我一些想法,那将大有帮助.

谢谢,

弗拉基米尔

解决方法:

手动创建递归下降解析器.很有趣！

首先定义一个语法：

Expression -> SimpleExpression ExpressionTail
              (Expression)
SimpleExpression -> Atom Inequality Atom
ExpressionTail -> && Expression |
                  || Expression |
                  e
Atom -> Variable | Literal
Inequality -> == | != | > | >= | < | <=

(此语法不处理运算符的优先级,但是很容易编写一个可以满足此要求的语法.)

接下来,创建一个词法分析器,该词法分析器将读取输入字符串并创建标记,以便将字符串“ var1！= 4.0”转换为{Variable,！=,Literal}的列表.可以将它们一起砍掉,或者如果您想花哨的话,可以使用有限状态机来分析字符串.

现在创建一个递归下降解析器,将标记列表解析为一个表达式树.

public class Parser {

    public Parser() {
    }

    public Expression parse( LexicalAnalyzer lex) {
        lex.advance();
        return expression( lex);
    }

    private Expression expression( LexicalAnalyzer lex) {  

        switch( lex.current().type() ) {
            case Token.OpenParen:
                lex.advance();
                Expression expression = expression( lex);
                lex.eat( Token.CloseParen);
                return expression;
            case Token.Literal:
            case Token.Variable:
                return expressionTail( lex, simpleExpression(lex));
            default:
                throw new Exception( "ParseError: Expecting (, variable, or literal at character " + 
                                      lex.character());
        }
    }

    private SimpleExpression simpleExpression( LexicalAnalyzer lex) {

        Atom atom = atom( lex);
        switch( lex.current().type() ) {
            case Token.Equal:
                lex.advance();
                return new Equal( atom, atom(lex));
            case Token.NotEqual:
                lex.advance();
                return new NotEqual( atom, atom(lex));
            ...
            default:
                throw new Exception( "ParseError: Expecting ==, !=, <, <=, >, >= at" + 
                                     lex.character());
        }
     }

     private Expression expressionTail( LexicalAnalyzer lex, SimpleExpression expression) {

        switch( lex.current().type() ) {
            case Token.LogicalOr:
                lex.advance();
                return new OrExpression( expression, expression(lex) );
            case Token.LogicalAnd:
                lex.advance();
                return new AndExpression( expression, exptression(lex) );
            default:
                return expression;
        }
     }

     private Atom atom( LexicalAnalyzer lex) {
         switch( lex.current().type() ) {
             case Token.Literal:
                 Literal literal = new Literal( lex.current() );
                 lex.advance();
                 return literal;
             case Token.Variable:
                 Variable var = new Variable( lex.current() );
                 lex.advance();
                 return var;
             default:
                 throw new Exception("ParseError: ...");
          }
      }
}


public interface Expression {
    boolean evaluate( VariableValues values);
}

public interface SimpleExpression implements Expression {
}

public class Equal implements SimpleExpression {
    private final Atom left, right;
    public Equal( Atom left, Atom right) {
        this.left = left;
        this.right = right;
    }
    public boolean evaluate( VariableValues values) {
        return left.evaluate(values) == right.evaluate(values);
    }
}
public class NotEqual implements SimpleExpression {
    private final Atom left, right;
    public NotEqual( Atom left, Atom right) {
        this.left = left;
        this.right = right;
    }
    public boolean evaluate( VariableValues values) {
        return left.evaluate(values) != right.evaluate(values);
    }
}

public class OrExpression implements Expression {
    private final Expression left, right;

    public OrExpression( Expression left, Expression right) {
        this.left = left;
        this.right = right;
    }

    public boolean evaluate( VariableValues values) {
        return left.evaluate(values) || right.evaluate(values);
    }
}
public class AndExpression implements Expression {
    private final Expression left, right;

    public AndExpression( Expression left, Expression right) {
        this.left = left;
        this.right = right;
    }

    public boolean evaluate( VariableValues values) {
        return left.evaluate(values) && right.evaluate(values);
    }
}
public interface Atom {
    double evaluate( VariableValues values);
}
public class Literal implements Atom {
    private final double value;
    public Literal( double value) {
        this.value = value;
    }
    public double evaluate( VariableValues values) {
        return value;
    }
}
public class Variable implements Atom {
    private final String name;
    public Variable( String name) {
        this.name = name;
    }
    public double evaluate( VariableValues values) {
        return values.getValue( name);
    }
}