PL/0编译器(java version) – Symbol.java

   1:  package compiler;

   2:   

   3:  /**

   4:   * 采用全局变量sym来存储符号码，并用全局变量id和num来传递语义值

   5:   *

   6:   * @author jiangnan

   7:   *

   8:   */

   9:  public class Symbol {

  10:   

  11:      //各类符号码

  12:      public static final int nul = 0;                  //NULL

  13:      public static final int ident = 1;               //标识符

  14:      public static final int plus = 2;                //加号+

  15:      public static final int minus = 3;              //减号-

  16:      public static final int mul = 4;                 //乘号*

  17:      public static final int div = 5;                  //除号/

  18:      public static final int oddsym = 6;           //odd

  19:      public static final int number = 7;           //数字

  20:      public static final int eql = 8;                  //等于号=(equal)

  21:      public static final int neq = 9;                 //不等于<>(not equal)

  22:      public static final int lss = 10;                 //小于<(less)

  23:      public static final int geq = 11;                 //大于等于>=(greater or equal)

  24:      public static final int gtr = 12;                //大于>(greater)

  25:      public static final int leq = 13;                //小于等于<=(less or equal)

  26:      public static final int lparen = 14;            //左括号(

  27:      public static final int rparen = 15;           //右括号 ) 

  28:      public static final int comma = 16;           //逗号,

  29:      public static final int semicolon = 17;       //分号;

  30:      public static final int peroid = 18;            //句号.

  31:      public static final int becomes = 19;         //赋值符号 :=

  32:      public static final int beginsym = 20;        //开始符号begin

  33:      public static final int endsym = 21;           //结束符号end

  34:      public static final int ifsym = 22;             //if

  35:      public static final int thensym = 23;         //then

  36:      public static final int whilesym = 24;        //while

  37:      public static final int writesym = 25;        //write

  38:      public static final int readsym = 26;         //read

  39:      public static final int dosym = 27;            //do

  40:      public static final int callsym = 28;          //call

  41:      public static final int constsym = 29;       //const

  42:      public static final int varsym = 30;           //var

  43:      public static final int procsym = 31;         //procedure

  44:      public static final int elsesym = 32;

  45:      public static final int repeatsym=33;

  46:      public static final int untilsym=34;

  47:      

  48:      //符号码的个数

  49:      public static final int symnum = 35;

  50:   

  51:      //设置保留字名字，按照字母顺序，便于折半查找

  52:      public static final String[] word = new String[]{

  53:          "begin","call" , "const"    , "do" ,

  54:          "else"  ,"end" ,"if"   , "odd", 

  55:          "procedure", "read","repeat","then",

  56:          "until" , "var", "while"    , "write" };

  57:      //保留字对应的符号值

  58:      public static final int[] wsym = new int[]{

  59:          beginsym, callsym, constsym, dosym,

  60:          elsesym, endsym, ifsym,oddsym, 

  61:          procsym,readsym,repeatsym, thensym,

  62:          untilsym ,varsym,whilesym, writesym};

  63:   

  64:      //符号码

  65:      public int symtype;

  66:      //标志符号名字；

  67:      public String id;

  68:      //数值的大小

  69:      public int num;

  70:   

  71:      /**

  72:       * 构造具有特定符号码的符号

  73:       *

  74:       * @param stype

  75:       */

  76:      public Symbol(int stype) {

  77:          symtype = stype;

  78:          id = "";

  79:          num = 0;

  80:      }

  81:  }

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