为什么Go中的程序包级别不允许短变量声明？

Question

This is allowed:

package main

var a = 3

...

But this isn't:

package main

a := 3

...

Why not? Why couldn't short variable declaration outside a function be treated regular declaration without a type? Just to simplify parsing?

Answer 1

According to Ian Lance Taylor in this thread shortly after the public announcement:

At the top level, every declaration begins with a keyword. This simplifies parsing.