java - 从解析器创建抽象树问题

Question

我需要很大的帮助，我有两个简单的类 Tree 和 Node (我只是在论坛上放置了接口(interface)以使用更少的空间，我可以轻松修改这些类)，我还有 Flex 文件和解析器文件，并且需要创建 AST(抽象语法树 - 将标记放入 Node 对象并以正确的方式填充 Tree )。

public class Tree {
    Node root;
    public void AddNode(Node n){}
    public void Evaluate(){}
}

public class Node {
    public String value;
    public int type;
    Node left, right;
}

这是解析器文件

import java_cup.runtime.*;

parser code {:

    public boolean result = true; 

    public void report_fatal_error(String message, Object   info) throws java.lang.Exception {
        done_parsing();
        System.out.println("report_fatal_error");
        report_error();
    }

    public void syntax_error(Symbol cur_token) {
        System.out.println("syntax_error");
        report_error();
    }

    public void unrecovered_syntax_error(Symbol cur_token) throws java.lang.Exception {
        System.out.println("unrecovered_syntax_error");
        report_fatal_error("Fatalna greska, parsiranje se ne moze nastaviti", cur_token);
    }

    public void report_error(){
        System.out.println("report_error");
        result = false;
    }
:}

init with {: result = true; :};

/* Terminals (tokens returned by the scanner). */
terminal           AND, OR, NOT;
terminal           LPAREN, RPAREN;
terminal           ITEM;
terminal           OPEN, CLOSE, MON, MOFF, TIMEOUT, ESERR, BAE, I, O, BUS, EXT, PUSHB;
terminal           VAL, OK, BUS_BR_L, BUS_BR_R, SH_CRT_L, SH_CRT_R, BUS_ALL, EXT_ALL, NO_TIMEOUT, NO_ES_ERR, IBUS_OK, CFG_OK, SYNTAX;
terminal           OUT;

/* Non-terminals */
non terminal        extension;
non terminal Integer    expr;

/* Precedences */
precedence left AND, OR;

/* The grammar */

expr      ::= 
          |
            expr:e1 AND expr:e2 
          {: 
            //System.out.println("AND"); 
            RESULT = 1; 
            :} 
          | 
              expr:e1 OR expr:e2 
          {: 
            //System.out.println("OR"); 
            RESULT = 2; 
            :} 
          | 
              NOT expr:e1
          {: 
            //System.out.println("NOT"); 
            RESULT = 3; 
            :}
          | 
              LPAREN expr:e RPAREN     
          {: 
            //System.out.println("()"); 
            RESULT = 4; 
            :} 
          | 
              ITEM extension:e1
          {: 
            //System.out.println("ITEM."); 
            RESULT = 5; 
            :}
          | 
              error
          {: 
            System.out.println("error"); 
            parser.report_error();
            RESULT = 0; 
            :}
          ;

extension ::= 
              OPEN
          |   
              MON
          |   
              CLOSE
          |
              MOFF
          |
              TIMEOUT
          |
              ESERR
          |
              BAE
          |
              I
          |
              O
          |
              BUS
          |
              EXT
          |
              PUSHB
          |
              VAL
          |
              OK
          |
              BUS_BR_L
          |
              BUS_BR_R
          |
              SH_CRT_L
          |
              SH_CRT_R
          |
              BUS_ALL
          |
              EXT_ALL
          |
              NO_TIMEOUT
          |
              NO_ES_ERR
          |
              IBUS_OK
          |
              CFG_OK 
          |
              SYNTAX
          | 
              OUT
          ;

这是语法

%%

%{
    public boolean result = true;

    //Puni expression sa tokenima radi reimenovanja
    public Expression expression=new Expression();
    //

    public ArrayList<String> items = new ArrayList<String>();
    public ArrayList<Integer> extensions = new ArrayList<Integer>();
    // ukljucivanje informacije o poziciji tokena
    private Symbol new_symbol(int type) {
            return new Symbol(type, yyline+1, yycolumn);
    }
    // ukljucivanje informacije o poziciji tokena
    private Symbol new_symbol(int type, Object value) {
            return new Symbol(type, yyline+1, yycolumn, value);
    }
%}

%cup

%xstate COMMENT

%eofval{ 
return new_symbol(sym.EOF);
%eofval}

%line
%column

%%
" " {}
"\b" {}
"\t" {}
"\r\n" {}
"\f" {}
"open" {extensions.add(sym.OPEN); return new_symbol(sym.OPEN);}
"close" {extensions.add(sym.CLOSE); return new_symbol(sym.CLOSE);}
"m_on" {extensions.add(sym.MON); return new_symbol(sym.MON);}
"m_off" {extensions.add(sym.MOFF); return new_symbol(sym.MOFF);}
"timeout" {extensions.add(sym.TIMEOUT); return new_symbol(sym.TIMEOUT);}
"es_err" {extensions.add(sym.ESERR); return new_symbol(sym.ESERR);}
"bae" {extensions.add(sym.BAE); return new_symbol(sym.BAE);}
"i" {extensions.add(sym.I); return new_symbol(sym.I);}
"o" {extensions.add(sym.O); return new_symbol(sym.O);}
"bus" {extensions.add(sym.BUS); return new_symbol(sym.BUS);}
"ext" {extensions.add(sym.EXT); return new_symbol(sym.EXT);}
"pushb" {extensions.add(sym.PUSHB); return new_symbol(sym.PUSHB);}
"val" {extensions.add(sym.VAL); return new_symbol(sym.VAL);}
"ok" {extensions.add(sym.OK); return new_symbol(sym.OK);}
"bus_br_l" {extensions.add(sym.BUS_BR_L); return new_symbol(sym.BUS_BR_L);}
"bus_br_r" {extensions.add(sym.BUS_BR_R); return new_symbol(sym.BUS_BR_R);}
"sh_crt_l" {extensions.add(sym.SH_CRT_L); return new_symbol(sym.SH_CRT_L);}
"sh_crt_r" {extensions.add(sym.SH_CRT_R); return new_symbol(sym.SH_CRT_R);}
"bus_all" {extensions.add(sym.BUS_ALL); return new_symbol(sym.BUS_ALL);}
"ext_all" {extensions.add(sym.EXT_ALL); return new_symbol(sym.EXT_ALL);}
"no_timeout" {extensions.add(sym.NO_TIMEOUT); return new_symbol(sym.NO_TIMEOUT);}
"no_es_err" {extensions.add(sym.NO_ES_ERR); return new_symbol(sym.NO_ES_ERR);}
"ibus_ok" {extensions.add(sym.IBUS_OK); return new_symbol(sym.IBUS_OK);}
"cfg_ok" {extensions.add(sym.CFG_OK); return new_symbol(sym.CFG_OK);}
"syntax" {extensions.add(sym.SYNTAX); return new_symbol(sym.SYNTAX);}
"out" {extensions.add(sym.OUT); return new_symbol(sym.OUT);}
"!" { return new_symbol(sym.NOT);}
"&" { return new_symbol(sym.AND);}
"|" { return new_symbol(sym.OR);}
"(" { return new_symbol(sym.LPAREN);}
")" { return new_symbol(sym.RPAREN);}
([[:jletter:]])[[:jletterdigit:]]* \. {items.add(yytext().substring(0, yytext().length()-1)); return new_symbol (sym.ITEM);}
. {result = false;}

问题是如何从这里创建 AST，我得到了类似于

的输入表达式

A.open && b.i ? Can anybody help ?

Answer 1

解析器中注释掉打印语句的行，例如:

        //System.out.println("OR"); 

是您想要使用现有的树数据结构维护 AST 的地方。根据您的语法找出哪个标记将创建树，在树中的某个位置添加一些内容等。