修改由Antlr生成的表达式? [英] Modify expressions, generated by Antlr?

问题描述

我想用Antlr4读取表达式并对其进行一些修改.

I would like to read expressions with Antlr4 and the perform some modifications on them.

例如，如果语法是算术的，我将修改表示形式的表达式

For example, if grammar is arithmetic, I would modify expression, representing

2 * (3 + 1)

使用

2 * 4

，然后使用

8

这是计算"或简化".要执行此操作，我将创建一些树结构，第一个想法是使用由Antlr创建的相同的树.

This is "calculation" or "simplification". To perform this thing I would create some tree structure and the first idea is to use the very same trees, created by Antlr.

不幸的是，我没有看到任何针对儿童的二传手.

Unfortunately, I don't see any setters for children.

如何完成?我真的应该用自己的树来复制Antlr树以表达逻辑吗?

How to accomplish? Should I really duplicate Antlr trees with my own ones for logic of expressions?

推荐答案

解决方案

您不应复制或修改ANTRL树.您应该通过使用树访问者和监听者模式使用它们.

首先，我们将为算术表达式准备简单的语法.

First we will prepare simple grammar for an arithmetic expression.

grammar expr;

WS : [ \t\r\n] -> skip;
INT : [0-9]+;

program
    : expr # baseExpr
    ;

expr
    : '(' expr ')'              # exprParentheses
    | left=expr '*' right=expr  # exprMul
    | left=expr '+' right=expr  # exprAdd
    | INT                       # exprINT
    ;

评估表达式

为了评估表达式，我们将遍历解析树以执行计算或收集结果.

Evaluate expression

In order to evaluate an expression, we will traverse the parse tree to perform a calculation or to collect the result.

public class EvaluateExpr extends exprBaseVisitor<Integer> {
    @Override
    public Integer visitExprINT(exprParser.ExprINTContext ctx) {
        return Integer.valueOf(ctx.INT().getText());
    }

    @Override
    public Integer visitExprMul(exprParser.ExprMulContext ctx) {
        Integer left = visit(ctx.left);
        Integer right = visit(ctx.right);
        return left * right;
    }

    @Override
    public Integer visitExprAdd(exprParser.ExprAddContext ctx) {
        Integer left = visit(ctx.left);
        Integer right = visit(ctx.right);
        return left + right;
    }

    @Override
    public Integer visitExprParentheses(exprParser.ExprParenthesesContext ctx) {
        return visit(ctx.expr());
    }
}

替换表达式

为了用表达式的赋值形式替换表达式，我们将使用TokenStreamRewriter类.该工具可轻松替换令牌.

Replace expression

In order to replace an expression with its evaluated form, we will use TokenStreamRewriter class. This tool allows for an easy substitution of tokens.

public class ReplaceExpr extends exprBaseListener {
    private TokenStreamRewriter rewriter;

    public ReplaceExpr(CommonTokenStream tokens) {
        rewriter = new TokenStreamRewriter(tokens);
    }

    @Override
    public void enterBaseExpr(exprParser.BaseExprContext ctx) {
        rewriter.replace(ctx.start, ctx.stop, new EvaluateExpr().visit(ctx));
    }

    public String getReplacedCode() {
        return rewriter.getText();
    }
}

运行示例

现在我们需要执行表达式的评估和替换.

Run the example

Now we need to perform evaluation and replacement of the expressions.

exprLexer lexer = new exprLexer(new ANTLRInputStream("2 * (3 + 1)"));
CommonTokenStream tokens = new CommonTokenStream(lexer);
exprParser parser = new exprParser(tokens);
ReplaceExpr replaceExpr = new ReplaceExpr(tokens);
ParseTreeWalker.DEFAULT.walk(replaceExpr, parser.program());
System.out.println("Replaced code: " + replaceExpr.getReplacedCode());

解析树或AST(抽象语法树)

如果您仍然需要修改后的解析树，则可以再次解析更改后的代码. 如果您想修改树形结构，请将解析树转换为 AST (抽象-语法树)，并从一开始就使用 AST .

The parse tree or AST (abstract-syntax tree)

If you still need a modified parse tree you can parse the altered code again. If you would like to modify the tree structure, convert the parse tree to the AST (abstract-syntax tree), and work on the AST from the start.

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