• (基于Java)编写编译器和解释器第5A章:基于Antlr解析表达式和赋值语句及计算(连载)


    本章在第3A章源代码基础上继续完善基于Antlr自动化的解析器,解释执行第5章解析的复合语句,赋值语句和表达式等相关中间码。并仿照第5章的简化标准,将一些东西简化掉,尽量能让你从最简处入手,掌握Antlr自动化构建解析器的第一步。

    ==>> 本章中文版源代码下载:svn co http://wci.googlecode.com/svn/branches/ch5_antlr/ 源代码使用了UTF-8编码,下载到本地请修改!

    好的工具事半功倍,Antlr亦如此。antlr.org上有一个很有特色的工具antlrwors。如果使用Eclipse,可以安装插件antlrv3ide。两个工具的主要特色是可视化的创建EBNF语法,就如同你在前面章节看到的语法图一样。对于我来说,比较习惯antlrworks,它有良好的调试功能和DFA分析功能。

    1 带AST构造的语法

       1: program: 
       2:   compound_statement DOT!;
       3: compound_statement: 
       4:   BEGIN statement_list END ->^(COMPOUND statement_list);
       5: assignment_statement:
       6:  ID ASSIGN expression -> ^(ASSIGN ID expression);
       7: statement:
       8:   compound_statement | assignment_statement;
       9: statement_list:
      10:   statement (SEMI statement)* SEMI? -> statement+;
      11: expression: 
      12:   simple_expression (rel_ops^ simple_expression)?;
      13: rel_ops:
      14:   LT | LE | GT | GE | NOT_EQUAL;
      15: simple_expression: 
      16:   signedterm (add_ops^ term)*;
      17: signedterm:
      18:   (a=PLUS | a=MINUS)? term ->{a!=null&&a.getType()==MINUS}?^(NEGATE term)->term;
      19: add_ops:
      20:   PLUS | MINUS | OR; 
      21: term:
      22:   factor (mul_ops^ factor)*;
      23: mul_ops:
      24:   STAR | SLASH | DIV | MOD | AND;
      25: factor:
      26:   ID | NUMBER | STRING | NOT^ factor | LPAREN! expression RPAREN!;

    目前的程序program由一个复合语句+结束的点"."组成。这个antlr语句基本与第五章的语法图5-1 和图5-2 类似。

    2 计算Token值

    填充第三章中关于计算常量token的值类ValueComputer,目前只对整数,字符串,浮点数token算值,算值逻辑与PascalStringToken和PascalNumberToken基本类似。

    详细参见代码ValueComputer,这里不再显示。

    3 引入符号表

    这里复用第5章的符号表。需要使用符号表的地方有两个,一个是赋值语句的左边变量作为定义出现,另外一个是表达式中的标识符作为引用出现。在Antlr分析中,一般符号表必须要在语法树构建完成后才能进行,因为语法树构建过程中的节点是不清晰的。在Antlr中构建完AST之后,将使用Antlr树语法(Tree Grammar)去遍历语法,这个过程中我们可以加入符号表操作,也可以执行动作和生成代码。

    4 执行赋值语句及计算语句

    我原本想只想演示一下相关分析树,但是发现过于简单,于是就干脆执行算了,执行第5章的分析树是第6章内容,所有没有6A章了。

    详细语法如下表:

       1: tree grammar PascalVisitor;
       2: options{
       3:   tokenVocab=Pascal;
       4:   ASTLabelType=PascalNode;
       5: }
       6: @header{
       7:   package com.lifesting.book.wci;
       8:   
       9:   import wci.intermediate.*;
      10:   import wci.intermediate.symtabimpl.SymTabKeyImpl;
      11: }
      12: @members{
      13:   protected SymTabStack symtabStack = SymTabFactory.createSymTabStack();
      14:   public SymTabStack getSymbolTableStack(){
      15:     return this.symtabStack;
      16:   }
      17: }
      18: program    : 
      19:   compound;
      20: compound :
      21:   ^(COMPOUND stmt+);
      22: stmt:
      23:   compound | assign;
      24: assign:
      25:   ^(ASSIGN i=ID e=expr){
      26:     String var = $i.text.toLowerCase();
      27:     SymTabEntry id_entry = symtabStack.lookup(var) ;
      28:     if (id_entry == null)
      29:     {
      30:       id_entry = symtabStack.enterLocal(var);
      31:     }
      32:     id_entry.setAttribute(SymTabKeyImpl.DATA_VALUE,e);
      33:   };
      34: expr returns[Object value]:
      35:   s=simple{value=s;} 
      36:   | ^(r=rel_ops e1=expr e2=expr){
      37:     if (e1 instanceof Number && e2 instanceof Number){
      38:       double de1 = ((Number)e1).doubleValue();
      39:       double de2 = ((Number)e2).doubleValue();
      40:       switch (r){
      41:         case 1:
      42:           value = de1 < de2;
      43:           break;
      44:         case 2:
      45:           value = de1 <= de2;
      46:           break;
      47:         case 3:
      48:           value = de1 > de2;
      49:           break;
      50:         case 4:
      51:           value = de1 >= de2;
      52:           break;
      53:         case 5:
      54:           value = de1 != de2;
      55:           break;
      56:         default:
      57:           break;
      58:       }
      59:     }else{
      60:       System.err.println("无法执行比较:"+e1+"["+r+"]"+e2);
      61:     }
      62:   };
      63: simple returns[Object value]:
      64:   s=term{value=s;} 
      65:   | ^(o=add_ops f1=negterm f2=simple) 
      66:   {
      67:     double df1 = Double.parseDouble(f1.toString());
      68:     if (f2 instanceof Number){
      69:       double df2 = Double.parseDouble(f2.toString());
      70:       switch (o)
      71:       {
      72:         case 1:
      73:           value = df1+df2;
      74:           break;
      75:         case 2:
      76:           value = df1-df2;
      77:           break;
      78:       }
      79:     }else{
      80:       System.err.println("不是一个数值:"+f2);
      81:     }
      82:   }
      83:   | ^(o=add_ops f1=simple f2=simple){
      84:      if (f1 instanceof Number && f2 instanceof Number){
      85:         double df1 = Double.parseDouble(f1.toString());
      86:         double df2 = Double.parseDouble(f2.toString());
      87:         switch (o){
      88:           case 1:
      89:             value = df1+df2;
      90:             break;
      91:           case 2:
      92:             value = df1-df2;
      93:             break;
      94:           default:
      95:             break;
      96:         }
      97:      }else if (f1 instanceof Boolean && f2 instanceof Boolean){
      98:        value= ((Boolean)f1).booleanValue() || ((Boolean)f2).booleanValue();
      99:      }else{
     100:        System.err.println("不能执行simple运算,f1="+f1+",f2="+f2);
     101:      }
     102:   };
     103:   
     104:   
     105: negterm returns[Object value]:
     106:   ^(NEGATE n=term) {
     107:     if(n instanceof Number){
     108:       return -Double.parseDouble(n.toString());
     109:     }else{
     110:       System.err.println("不是一个数值:"+n);
     111:       value = 0.0;
     112:     }
     113:   };
     114:   
     115: term returns[Object value]:
     116:   f0=factor{value=f0;} 
     117:   | ^(t=mul_ops f1=factor f2=factor){
     118:     if (f1 instanceof Number && f2 instanceof Number){
     119:       double df1 = Double.parseDouble(f1.toString());
     120:       double df2 = Double.parseDouble(f2.toString());
     121:       switch (t){
     122:         case 1:
     123:           value= df1*df2;
     124:           break;
     125:         case 2:
     126:         case 3:
     127:           value= df1/df2;
     128:         case 4:
     129:           value=df1 \% df2;
     130:         default:
     131:           break;
     132:       }
     133:     }else if (f1 instanceof Boolean && f2 instanceof Boolean){
     134:       value= ((Boolean)f1).booleanValue() && ((Boolean)f2).booleanValue();
     135:     }else{
     136:       System.err.println("不能执行term运算,f1="+f1+",f2="+f2);
     137:     }
     138:   };
     139:   
     140: factor returns[Object value]:
     141:   i = ID{
     142:     String var = $i.text.toLowerCase();
     143:     SymTabEntry id_entry = symtabStack.lookup(var);
     144:     if (id_entry == null){
     145:       System.err.println("使用不存在的变量:"+var);
     146:     }else{
     147:       value = id_entry.getAttribute(SymTabKeyImpl.DATA_VALUE);
     148:     }
     149:   } 
     150:   | n=NUMBER{value =((PascalAntlrToken)$n.getToken()).getValue();} 
     151:   | r=NUMBER_REAL{value = ((PascalAntlrToken)$r.getToken()).getValue();}
     152:   | s=STRING {value =((PascalAntlrToken)$s.getToken()).getValue(); }
     153:   | ^(NOT f=factor) { 
     154:       if (f instanceof Boolean){
     155:         value = !((Boolean)f).booleanValue();
     156:       }else{
     157:         System.err.println("不是一个布尔值:"+f);
     158:       }
     159:     }
     160:   
     161:   | ^(NESTEXPR e = expr){
     162:       value = e;
     163:     }; 
     164:   
     165: rel_ops returns [int type]:
     166:   LT{type =1;} | LE{type = 2;} | GT{type=3;} | GE{type=4;} | NOT_EQUAL{type=5;};
     167: add_ops returns [int type]:
     168:   PLUS{type=1;} | MINUS{type=2;} | OR{type=3;}; 
     169: mul_ops returns [int type]:
     170:   STAR{type = 1;} | SLASH{type=2;} | DIV{type=3;} | MOD{type=4;} | AND{type=5;};

    测试程序:

       1: public final class SimpleInterpreter {
       2:     public static void main(String[] args) throws IOException, RecognitionException {
       3:         //第5章示例Pascal
       4:         InputStreamReader stream = new InputStreamReader(ShowToken.class.getResourceAsStream("/assignments.txt"));
       5:         ANTLRReaderStream reader = new ANTLRReaderStream(stream);
       6:         //词法分析器
       7:         PascalLexer lexer = new PascalLexer(reader);
       8:         CommonTokenStream token_stream = new CommonTokenStream(lexer);
       9:         //语法分析器并带自己的TreeAdaptor,转换成自己的PascalNode
      10:         PascalParser parser = new PascalParser(token_stream);
      11:         parser.setTreeAdaptor(new PascalNodeAdaptor());
      12:         program_return prog = parser.program();
      13:         //遍历树并运算
      14:         TreeNodeStream node_stream  = new CommonTreeNodeStream(prog.getTree());
      15:         PascalVisitor interpreter = new PascalVisitor(node_stream);
      16:         interpreter.program();
      17:         SymTabStack stack = interpreter.getSymbolTableStack();
      18:         SymTabEntry five_entry = stack.lookup("five");
      19:         System.out.println("Five = "+five_entry.getAttribute(SymTabKeyImpl.DATA_VALUE));
      20:         SymTabEntry str_entry = stack.lookup("str");
      21:         System.out.println("str = "+str_entry.getAttribute(SymTabKeyImpl.DATA_VALUE));
      22:         SymTabEntry  fahrenheit_entry = stack.lookup("fahrenheit");
      23:         System.out.println("fahrenheit = "+fahrenheit_entry.getAttribute(SymTabKeyImpl.DATA_VALUE));
      24:         SymTabEntry centigrade_entry = stack.lookup("centigrade");
      25:         System.out.println("centigrade = "+centigrade_entry.getAttribute(SymTabKeyImpl.DATA_VALUE));
      26:     }
      27: }

    最后的输出结果:

    Five = 5.0
    str = 'hello, world'
    fahrenheit = 32.0
    centigrade = 25
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  • 原文地址:https://www.cnblogs.com/lifesting/p/2603929.html
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