mea culpa on the eval/expr. I did the comments inline for brevity.

I am confused about the $$ examples though, since swear I have worked on production code that literally behaves like that. Maybe they had some extra non-alphanumeric bits. This behaves the way I gave originally

    set b a
    set (a) 5

    puts $($b)

Edit: I found the production code. There was both

    puts [expr 3 - $$b]

and

    puts [subst $$b]

and the Steve example was actually two steps:

    set nameVariable [subst var$$b]
    puts  [subst $$nameVariable]