if.java

编译原理“龙书”(Compilers: Principles, Techniques, and Tools)中提供的一个小型Syntax-Directed Translator

package inter;
import symbols.*;

public class If extends Stmt {

   Expr expr; Stmt stmt;

   public If(Expr x, Stmt s) {
      expr = x;  stmt = s;
      if( expr.type != Type.Bool ) expr.error("boolean required in if");
   }

   public void gen(int b, int a) {
      int label = newlabel(); // label for the code for stmt
      expr.jumping(0, a);     // fall through on true, goto a on false
      emitlabel(label); stmt.gen(label, a);
   }
}