如何从JISON解析器中获取抽象语法树（AST）？ [英] How to get Abstract Syntax Tree (AST) out of JISON parser?

问题描述

所以我通过JISON生成了一个解析器：

So I have generated a parser via JISON:

// mygenerator.js
var Parser = require("jison").Parser;

// a grammar in JSON
var grammar = {
    "lex": {
        "rules": [
           ["\\s+", "/* skip whitespace */"],
           ["[a-f0-9]+", "return 'HEX';"]
        ]
    },

    "bnf": {
        "hex_strings" :[ "hex_strings HEX",
                         "HEX" ]
    }
};

// `grammar` can also be a string that uses jison's grammar format
var parser = new Parser(grammar);

// generate source, ready to be written to disk
var parserSource = parser.generate();

// you can also use the parser directly from memory

// returns true
parser.parse("adfe34bc e82a");

// throws lexical error
parser.parse("adfe34bc zxg");

我的问题是，我现在如何检索AST？我可以看到我可以针对输入运行解析器，但是如果它工作则返回true，否则返回true。

My question is, how do I retrieve the AST now? I can see that I can run the parser against input, but it just returns true if it works or fails if not.

对于记录，我使用的是JISON：< a href =http://zaach.github.com/jison/docs/ =noreferrer> http://zaach.github.com/jison/docs/

For the record, I am using JISON: http://zaach.github.com/jison/docs/

推荐答案

我对Jison的内部工作方式不太熟悉，所以我不知道会采用哪种方法。

I'm not too familiar with Jison's inner workings, so I don't know any method that would do it.

但是如果你对一点点暴力感兴趣来解决这个问题，试试这个：

But in case you're interested in a little bruteforce to solve this problem, try this:

首先，创建一个对象来保存AST

First, create an object to hold the AST

function jisonAST(name, x) { this.name = name; this.x = x; }

// return the indented AST
jisonAST.prototype.get = function(indent){
  // create an indentation for level l
  function indentString(l) { var r=""; for(var i=0;i<l;i++){r+="  "}; return r }

  var r = indentString(indent) + "["+this.name+": ";
  var rem = this.x;
  if( rem.length == 1 && !(rem[0] instanceof jisonAST) ) r += "'"+rem[0]+"'"; 
  else for( i in rem ){ 
      if( rem[i] instanceof jisonAST ) r += "\n" + rem[i].get(indent+1);
      else { r += "\n" + indentString(indent+1); r += "'"+rem[i]+"'"; }
    }
  return r + "]";
}

为Jison的BNF添加一个小帮手函数

Add a little helper function for Jison's BNF

function o( s ){
    r = "$$ = new yy.jisonAST('"+s+"',[";
    for( i = 1; i <= s.split(" ").length; i++ ){ r += "$"+i+"," }
    r = r.slice(0,-1) + "]);";
    return [s,r];
}

有了这个，请继续使用示例代码（稍作修改）：

With this, continue to the example code (slight modification):

var Parser = require("jison").Parser;

// a grammar in JSON
var grammar = {
    "lex": {
        "rules": [
           ["\\s+", "/* skip whitespace */"],
           ["[a-f0-9]+", "return 'HEX';"]
        ]
    },
    "bnf": {
        // had to add a start/end, see below
        "start" : [ [ "hex_strings", "return $1" ] ],
        "hex_strings" :[ 
            o("hex_strings HEX"), 
            o("HEX") 
        ]
    }
};

var parser = new Parser(grammar);
// expose the AST object to Jison
parser.yy.jisonAST = jisonAST

现在你可以尝试解析：

console.log( parser.parse("adfe34bc e82a 43af").get(0) );

这将给你：

[hex_strings HEX: 
  [hex_strings HEX: 
    [HEX: 'adfe34bc']  
    'e82a']  
  '43af']

小笔记：我必须添加一个开始规则，以便只有一个语句返回结果。它不干净（因为没有它，BNF工作正常）。将其设置为切入点以确保...

Small note: I had to add a "start" rule, in order to only have one statement that returns the result. It is not clean (since the BNF works fine without it). Set it as an entry point to be sure...

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