语法2 will 与be going to do 

1、will  + 动词原形

表示将来的动作或状态。

You will feel better after taking this medicine.

Do you think it will rain?　

I will not lend the book to you.

Take it easy，I will not do it any longer.

2、be going to +动词原形

一是表示“意图”，即打算在最近的将来或将来进行某事。

Are you going to post that letter? 

How long is he going to stay here?

I am going to book a ticket.

另一意义是表示“预见”，即现在已有迹象表明将要发生或即将发生某种情况。

It's going to rain.

George is putting on weight; he is going to be quite fat.  

3、be doing

用be doing表示将来：主要意义是表示按计划、安排即将发生的动作，常用于位置转移的动词。

如：go，come，leave，arrive等，也可用于其他动作动词。We are having fish for dinner.We are moving to a different hotel the day after tomorrow.这种用法通常带有表示将来的时间状语，如果不带时间状语，则根据上下文可表示最近即将发生的动作。

A: Where are you going?

B: I am going for a walk. Are you coming with me?

A: Yes，I am just coming. Wait for me.