（1）
The empty string is written “”, and is a synonym for [].
举例如下：
> "" == []
True
（2）
Since a string is a list of characters, we can use the regular list operators to construct new strings.
举例如下：
> 'a':"bc"
"abc"
> "foo" ++ "bar"
"foobar"
（1）
The empty string is written “”, and is a synonym for [].
举例如下：
> "" == []
True
（2）
Since a string is a list of characters, we can use the regular list operators to construct new strings.
举例如下：
> 'a':"bc"
"abc"
> "foo" ++ "bar"
"foobar"