ANTLR4 AST创建-如何创建AstVistor [英] ANTLR4 AST Creation - How to create an AstVistor
问题描述
借助此问题如何使用ANTLR4创建AST?我能够创建AST节点,但是如我所接受的答案示例所示,我一直坚持对 BuildAstVisitor
进行编码。
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.
我有一个这样的语法:
mini: (constDecl | varDef | funcDecl | funcDef)* ;
而且我都无法为标签分配标签(antlr4说 label X分配给不是集合的块
),而我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());
}
上面的代码存在以下问题:我不知道如何确定是 constDecl
, varDef
还是任何其他选项以及 ctx.constDecl()
返回 List< ConstDeclContext>
,而 visitConstDecl
函数只需要一个元素。
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.
编辑:
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]+ ;
// ...
我仍然不确定如何实施 BuildAstVisitor
。我现在有以下内容,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
如果要获取各个子规则然后为它们实现visitXXX函数( visitConstDecl()
, visitVarDef()
等),而不是 visitMini()
函数。只有在输入中确实存在匹配项时,它们才会被调用。因此,您不需要进行任何检查。
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.
这篇关于ANTLR4 AST创建-如何创建AstVistor的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!