1  typedef enum
       2  {
       3    END = -1,
       4    EMPTY = (1 << 8 ) ,
       5    BACKREF,
       6    BEGLINE,
       7    ENDLINE,
       8    BEGWORD,
       9    ENDWORD,
      10    LIMWORD,
      11    NOTLIMWORD,
      12    QMARK,
      13    STAR,
      14    PLUS,
      15    REPMN,
      16    CAT,
      17    OR,
      18    ORTOP,
      19    LPAREN,
      20    RPAREN,
      21    CSET
      22  } token;
      23  
      24  static token tok;
      25  
      26  static int
      27  atom ()
      28  {
      29    if ((tok >= 0 && tok < (1 << 8 ) ) || tok >= CSET || tok == BACKREF
      30        || tok == BEGLINE || tok == ENDLINE || tok == BEGWORD
      31        || tok == ENDWORD || tok == LIMWORD || tok == NOTLIMWORD)
      32      return 1;
      33    else
      34      return 0;
      35  }
      36  
      37  main ()
      38  {
      39    tok = 0;
      40    if (atom () != 1)
      41      abort ();
      42    exit (0);
      43  }