/* La classe astratta Expr definisce parse tree per le espressioni.
   Le sottoclassi concrete si riferiscono ai tipi particolari di
   espressioni.
   In questa versione gli identificatori vengono posti in una symbol
   table.
*/

abstract class Expr {

  public abstract int calcola();

}


class PiuExpr extends Expr {
  private Expr sx, dx;

  public PiuExpr(Expr sx, Expr dx) {
    this.sx = sx;
    this.dx = dx;
  }

  public int calcola() {
    return sx.calcola() + dx.calcola();
  }

  public String toString() {
    return sx.toString() + " " + dx.toString() + " +";
  }
}


class MenoExpr extends Expr {
  private Expr sx, dx;

  public MenoExpr(Expr sx, Expr dx) {
    this.sx = sx;
    this.dx = dx;
  }

  public int calcola() {
    return sx.calcola() - dx.calcola();
  }

  public String toString() {
    return sx.toString() + " " + dx.toString() + " -";
  }
}


class PerExpr extends Expr {
  private Expr sx, dx;

  public PerExpr(Expr sx, Expr dx) {
    this.sx = sx;
    this.dx = dx;
  }

  public int calcola() {
    return sx.calcola() * dx.calcola();
  }

  public String toString() {
    return sx.toString() + " " + dx.toString() + " *";
  }
}


class DivisoExpr extends Expr {
  private Expr sx, dx;

  public DivisoExpr(Expr sx, Expr dx) {
    this.sx = sx;
    this.dx = dx;
  }

  public int calcola() {
    return sx.calcola() / dx.calcola();
  }

  public String toString() {
    return sx.toString() + " " + dx.toString() + " /";
  }
}


class UnMenoExpr extends Expr {
  private Expr e;

  public UnMenoExpr(Expr e) {
    this.e = e;
  }

  public int calcola() {
    return -e.calcola();
  }

  public String toString() {
    return e.toString() + "-";
  }
}


class UnPiuExpr extends Expr {
  private Expr e;

  public UnPiuExpr(Expr e) {
    this.e = e;
  }

  public int calcola() {
    return e.calcola();
  }

  public String toString() {
    return e.toString() + "+";
  }
}


class NumExpr extends Expr {
  private Integer num;

  public NumExpr(Integer num) {
    this.num = num;
  }

  public int calcola() {
    return num.intValue();
  }
  
  public String toString() {
    return num.toString();
  }
}


class IdExpr extends Expr {
  private Descrittore descrittore;

  public IdExpr(Descrittore d) {
    descrittore = d;
  }

  public int calcola() {
    return descrittore.getValore();
  }

  public String toString() {
    return descrittore.getIdentificatore();
  }
}