tboolexp.java

java语法解释器生成器

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright (C) 2001       Gerwin Klein <[e-mail]>                    *
 * Copyright (C) 2001       Bernhard Rumpe <[e-mail]>               *
 * All rights reserved.                                                    *
 *                                                                         *
 * This program is free software; you can redistribute it and/or modify    *
 * it under the terms of the GNU General Public License. See the file      *
 * COPYRIGHT for more information.                                         *
 *                                                                         *
 * This program is distributed in the hope that it will be useful,         *
 * but WITHOUT ANY WARRANTY; without even the implied warranty of          *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           *
 * GNU General Public License for more details.                            *
 *                                                                         *
 * You should have received a copy of the GNU General Public License along *
 * with this program; if not, write to the Free Software Foundation, Inc., *
 * 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA                 *
 *                                                                         *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */


/**
 * AST node for bool expressions
 */ 
class Tboolexp implements AST {
  Texp exp1, exp2;            // left and right subexpression 
  char kind;                  // '=', '<' and '!' for "<="

  public Tboolexp(Texp e1, char k, Texp e2) {
    exp1=e1;
    kind=k;
    exp2=e2;
  }

  public String toString() {
    if (kind!='!') 
      return(""+exp1+kind+exp2);
    else 
      return(exp1+"<="+exp2);
  }

  public void checkcontext(SymTab st) { // context conditions 
    exp1.checkcontext(st);
    exp2.checkcontext(st);
  }

  public void prepInterp(SymTab st) {   // set pointers and indices
    exp1.prepInterp(st);
    exp2.prepInterp(st);
  }

  public boolean interpret(int[] in, int[] par) {
    int e1 = exp1.interpret(in,par);
    int e2 = exp2.interpret(in,par);
    switch(kind) {
    case '=': return(e1==e2);
    case '<': return(e1<e2);
    case '!': return(e1<=e2);
    }

    return(false);     // error
  }
}