/* SetExpr.java */

/** A class to represent assignment statements in the expression language. */
public class SetExpr extends Expression {

  /* Constructs a SetExpr object in which var is being assigned the 
   * Value val.  (We might write such assignments as "var = val" in 
   * some langauges, although ours will use "(set var val)".  
   * @param var is the variable to be assigned.
   * @param val is a value to which var is assigned.  Note that 
   *   val is an arbitrary Expression, not necessary a ValueExpr.
   */
  public SetExpr(Expression var, Expression val) {
    /* Fill in for part 2. */
  }

  public int arity() { 
    return 2;
  }

  public String oper() { 
    return "set";
  }

  public Expression operand(int i) {   
    /* Fill in for part 2. */
  }
   
  public Value eval() {
    /* Fill in for part 2. */
  }
}