要实现ANTLR递归替换,首先需要编写一个ANTLR语法文件,然后使用ANTLR工具生成相应的解析器和词法分析器。接下来,可以通过编写一个ANTLR的访问者类来遍历解析树,并实现递归替换的逻辑。
下面是一个示例:
grammar myGrammar;
expression : '(' expression ')' # parentheses
| expression op expression # binaryOp
| ID # identifier
;
op : '+' | '-' | '*' | '/';
ID : [a-zA-Z]+;
antlr4 myGrammar.g4
javac *.java
import org.antlr.v4.runtime.tree.TerminalNode;
import myGrammarParser.*;
public class MyVisitor extends myGrammarBaseVisitor {
@Override
public Expression visitParentheses(ParenthesesContext ctx) {
Expression expression = visit(ctx.expression());
return new ParenthesesExpression(expression);
}
@Override
public Expression visitBinaryOp(BinaryOpContext ctx) {
Expression leftExpression = visit(ctx.expression(0));
Expression rightExpression = visit(ctx.expression(1));
return new BinaryOpExpression(leftExpression, ctx.op.getText(), rightExpression);
}
@Override
public Expression visitIdentifier(IdentifierContext ctx) {
TerminalNode terminalNode = (TerminalNode) ctx.getChild(0);
return new IdentifierExpression(terminalNode.getText());
}
}
import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
import myGrammarParser.*;
public class Main {
public static void main(String[] args) throws Exception {
String expressionString = "(a + b) * c";
ANTLRInputStream input = new ANTLRInputStream(expressionString);
myGrammarLexer lexer = new myGrammarLexer(input);
CommonTokenStream tokens = new CommonTokenStream(lexer);
myGrammarParser parser = new myGrammarParser(tokens);
ParseTree tree = parser.expression();
MyVisitor visitor = new MyVisitor();
Expression expression = visitor.visit(tree);
// 递归替换示例
Expression replacedExpression = replaceIdentifier(expression, "a", new IdentifierExpression("x"));
System.out.println(replacedExpression);
}
private static Expression replaceIdentifier(Expression expression, String oldIdentifier, Expression newExpression) {
if (expression instanceof IdentifierExpression) {
IdentifierExpression identifierExpression = (IdentifierExpression) expression;
if (identifierExpression.getIdentifier().equals(oldIdentifier)) {
return newExpression;
}
} else if (expression instanceof ParenthesesExpression) {
ParenthesesExpression parenthesesExpression = (ParenthesesExpression) expression;
Expression innerExpression = replaceIdentifier(parenthesesExpression.getExpression(), oldIdentifier, newExpression);
return new ParenthesesExpression(innerExpression);
} else if (expression instanceof BinaryOpExpression) {
BinaryOpExpression binaryOpExpression = (BinaryOpExpression) expression;
Expression leftExpression = replaceIdentifier(binaryOpExpression.getLeftExpression(), oldIdentifier, newExpression);
Expression rightExpression = replaceIdentifier(binaryOpExpression.getRightExpression(), oldIdentifier, newExpression);
return new BinaryOpExpression(leftExpression, binaryOpExpression.getOperator(), rightExpression);
}
return expression;
}
}
以上示例演示了如何使用ANTLR来解析一个表达式,并使用访问者模式实现递归替换。在主程序中,我们创建了一个标识符替换的示例,将表达式中的标识符"a"替换为一个新的表达式"x"。
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