Will suspend evaluation of current code block, but allow
the event loop to continue handling pending events.

This particular version of uniqkey is my favorite
because the keys generated will generally sort in
time created order.

 proc uniqkey { } {
     set key   [ expr { pow(2,31) + [ clock clicks ] } ]
     set key   [ string range $key end-8 end-3 ]
     set key   [ clock seconds ]$key
     return $key
 }
 
 proc sleep { ms } {
     set uniq [ uniqkey ]
     set ::__sleep__tmp__$uniq 0
     after $ms set ::__sleep__tmp__$uniq 1
     vwait ::__sleep__tmp__$uniq
     unset ::__sleep__tmp__$uniq
 }

Example:
 after 4000 puts foo!
 sleep 5000
 puts bar!

'''-[Phil Ehrens]'''