ANTLR4 AST 创建 - 如何创建 AstVistor [英] ANTLR4 AST Creation - How to create an AstVistor

问题描述

借助这个 SO 问题如何使用 ANTLR4 创建 AST? 我能够创建 AST 节点，但我一直坚持编写 BuildAstVisitor，如已接受的答案示例中所述.

With the help of this SO question How to create AST with ANTLR4? I was able to create the AST Nodes, but I'm stuck at coding the BuildAstVisitor as depicted in the accepted answer's example.

我有一个这样开头的语法:

I have a grammar that starts like this:

mini: (constDecl | varDef | funcDecl | funcDef)* ;

而且我既不能给块分配标签(antlr4说标签X分配给一个不是集合的块)，我也不知道如何访问下一个节点.>

And I can neither assign a label to the block (antlr4 says label X assigned to a block which is not a set), and I have no idea how to visit the next node.

public Expr visitMini(MiniCppParser.MiniContext ctx) {
    return visitConstDecl(ctx.constDecl());
}

我上面的代码有以下问题:我不知道如何决定它是 constDecl、varDef 还是任何其他选项和 ctx.constDecl() 返回一个 List 而我只需要一个元素用于 visitConstDecl 函数.

I have the following problems with the code above: I don't know how to decide whether it's a constDecl, varDef or any other option and ctx.constDecl() returns a List<ConstDeclContext> whereas I only need one element for the visitConstDecl function.

更多语法规则:

mini: (constDecl | varDef | funcDecl | funcDef)* ;

//--------------------------------------------------

constDecl:   'const' type ident=ID init ';' ;
init:        '=' ( value=BOOLEAN | sign=('+' | '-')? value=NUMBER ) ;
// ...

//--------------------------------------------------

OP_ADD: '+';
OP_SUB: '-';
OP_MUL: '*';
OP_DIV: '/';
OP_MOD: '%';

BOOLEAN        : 'true' | 'false' ;
NUMBER         : '-'? INT ;
fragment INT   : '0' | [1-9] [0-9]* ;
ID             : [a-zA-Z]+ ;
// ...

我仍然不完全确定如何实现 BuildAstVisitor.我现在有一些类似于以下内容的内容，但对我来说肯定不正确......

I'm still not entirely sure on how to implement the BuildAstVisitor. I now have something along the lines of the following, but it certainly doesn't look right to me...

@Override
public Expr visitMini(MiniCppParser.MiniContext ctx) {
  for (MiniCppParser.ConstDeclContext constDeclCtx : ctx.constDecl()) {
    visit(constDeclCtx);
  }
  return null;
}

@Override
public Expr visitConstDecl(MiniCppParser.ConstDeclContext ctx) {
  visit(ctx.type());
  return visit(ctx.init());
}

推荐答案

如果你想获得单独的子规则，那么为它们实现visitXXX函数(visitConstDecl(), visitVarDef() 等)而不是 visitMini() 函数.只有在输入中确实匹配它们时才会调用它们.因此，您无需对出现的情况进行任何检查.

If you want to get the individual subrules then implement the visitXXX functions for them (visitConstDecl(), visitVarDef() etc.) instead of the visitMini() function. They will only be called if there's really a match for them in the input. Hence you don't need to do any checks for occurences.

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