> That rosetta code has NO static scoping

That was the point! I pasted it as an example of what you can do with upvar, by bypassing lexical scoping. Take a look at other entries on that page: almost all high-level languages either pack the two variables into a list of some kind (passed by reference) or have a specialized language construct for this (inout etc.)

> neither has Tcl

This is very easy to disprove, take a look. This code:

    proc g {} {
        echo $a
    }

    proc f {} {
        set a 10
        g
    }

    f

results in an error in Tcl:

    can't read "a": no such variable
        while executing
    "echo $a"
        (procedure "g" line 2)
        invoked from within
    "g"
        (procedure "f" line 3)
        invoked from within
    "f"
        (file "main.tcl" line 35)

while in a dynamically scoped language, like Emacs Lisp, it would work:

    (defun g ()
      (message "%s" a))

    (defun f ()
      (let ((a 10))
        (g)))

    (f)

How can you argue with that, I wonder? :)

> just a really bad one.

It (upvar and uplevel) lets you easily define new control structures (think "unless", "until", "await", things like these). I don't think you can convince me that adding a powerful feature to the language is a bad decision... but that's indeed a matter of preference and there are people who use Go, so I'm not going to argue about this :)