Variables declared within the main body of a [coroutine] persist for the life of the coroutine.  This much is obvious.  What may be less obvious is that you can access those variables from commands called from the coro, using [[[upvar] #1]], so here's a little wrapper to facilitate that:

======
    proc corovars {args} {
        foreach n $args {lappend v $n $n}
        uplevel 1 [list upvar #1 {*}$v]
    }
======

So, coro-persistent variables may be declared thus within procs:

======
    corovars x y z
======

[MS] a variant that builds the list in a more direct manner is
    
======
    proc corovars {args} {
        set cmd [list upvar #1]
        foreach n $args {lappend cmd $n $n}
        uplevel 1 $cmd
    }
======

[AMG]: I use this trick in [Wibble]; it's very helpful.  See [[::wibble::cleanup]] in [Wibble implementation].  See [WebSocket] for more examples of use.

<<categories>>Dev. tools