assign.java

symbman（大学作业）

public class Assign extends Expression {
	
	private Symbol s;
	private Expression e;
	
	public Assign(Symbol s, Expression e) {
		this.s = (Symbol)s.clone();
		this.e = (Expression)e.clone();
	}
	
	public Symbol getSymbol() { return s; }
	
	public Expression getExpression() { return e; }
	
	public Expression eval() {
		Expression ev = e.eval();
		Memory.write(s, ev);
		return ev;
	}
	
	public Object clone() {
		return new Assign(s, e);
	}
	
	public String toString() {
		return "(" + s + "=" + e +")";
	}
	
	public Expression derive(Symbol s) {
		return (e.eval()).derive(s);
	}
	
	public Expression simplify() {
		return new Assign(s, e.simplify());
	}
	
	public boolean equals(Expression ex) {
		if(!(e instanceof Assign)) return false;
		Assign a = (Assign)ex;
		if(!((a.getExpression()).equals(e))) return false;
		if(!((a.getSymbol()).equals(s))) return false;
		return true;
	}
	
}