public void setOperandAt(final Block block, final Expr expr) {
		final Expr operand = (Expr) operands.get(block);

		if (operand != null) {
			operand.cleanup();
		}

		if (expr != null) {
			operands.put(block, expr);
			expr.setParent(this);
		} else {
			operands.remove(block);
		}
	}