Before 

( ) express senses in a container associate in priority 

[ ] express a container for collection 

{ } express a container for classification 

After 

There is only one kind of bracket, and all kinds of containers are expressed by ( ) .

[ ] { } are turned to operators:  

A [ B expersses A is an element of collection B 

A ] B expersses A is a collection of element B 

A { B expersses A is an instance of class B 

A } B expersses A is a class of instance B