Some of my best programming stories are from hacking TCL on Aolserver. The ability to make up language constructs was so powerful, and something I haven't seen anywhere else - full disclosure, I haven't used lisp yet, but it looks uglier to me than TCL and a clean programmer can produce very nice looking TCL code.

Among other things I remember adding named parameters to tcl procs in like a few hours - a feature some other languages consider a plus.

Is it missing in TCL? Just add it yourself :)