[NEM] '''15Feb2004''' - Just knocked up these replacements for [split] and [join] that allow nested lists to be dealt with. The implementations are recursive, and so not terribly efficient, but they could have uses. Might be a possibility for a TIP...

[NEM] '''6June2005''' - Improved the implementation a bit.

Some usage examples:

 % set ret [multi::join {
   {Person {name "Neil Madden"} {age 24} {occupation "Research Associate"} }
   {Person {name "Foo Bar"} {age 99} {occupation "Example"} }
 } \n : = _]
 Person:name=Neil_Madden:age=24:occupation=Research_Associate
 Person:name=Foo_Bar:age=99:occupation=Example
 % join [multi::split $ret \n : = _] \n
 Person {name {Neil Madden}} {age 24} {occupation {Research Associate}}
 Person {name {Foo Bar}} {age 99} {occupation Example}

''The Code:''

Sorry about the poor choice of namespace, but I was doing this in a hurry. If you think of a better name, change it...

 package provide multi 1.0
 namespace eval multi { }
 proc ::multi::join {list args} {
    if {[llength $args] < 2} {
        eval [linsert $args 0 ::join $list]
    } else {
        set ret [list]
        set next [lrange $args 1 end]
        foreach item $list { lappend ret [eval [linsert $next 0 join $item]] }
        return [::join $ret [lindex $args 0]]
    }
 }
 proc ::multi::split {string args} {
    if {[llength $args] < 2} {
        eval [linsert $args 0 ::split $string]
    } else {
        set ret [list]
        set next [lrange $args 1 end]
        foreach item [::split $string [lindex $args 0]] {
            lappend ret [eval [linsert $next 0 split $item]]
        }
        return $ret
    }
 }