[827a]

I overall like it and would prefer a world where Go had this spec implemented versus did not.

Criticism:

> Within the block a new variable err is implicitly declared, possibly shadowing other variables named err

Shadowing here is strange, and I would prefer a design where it did not shadow other variables named err, but rather threw a compiler error concerning the re-declaration of a variable. That would effectively mean that you can't mix-and-match this syntax with old error-handling inside one function, because code like this would fail to compile:

    func Test() {
      user, err := GetUser("12345")
      if err != nil {
        panic(err)
      }
      EmailUser(user) ? {
        panic(err)
      }
    }

I'm fearful the shadowing will be confusing, because one might try to reference that shadowed error within the block in (rare) situations where you need to return the synthesis of two error values, and you'll need to know the trivia of: `err` is a special name, I shouldn't name that shadowed variable `err`, let me name it `err2`. Granted: throwing a compiler error would also disallow this and force you to name the first variable `err2`; but at least the compiler is telling you the problem, rather than relying on your knowledge of new trivia.

[bpt3]

I don't care for this spec and probably wouldn't use it if it were implemented, but I do like your suggestion of how to handle err shadowing.