[alhimik45]

>refcounting does the job since no cycles are possible by design

So double-linked list is impossible to define?

[BoingBoomTschak]

You can't define new data structures as such in pure Tcl, as you don't have pointers. And as for cycles, you can't modify an object to add a reference to itself, since the copy-on-write will just create a new object.

[sigzero]

Rosetta Code has examples of DBLs in Tcl and Tcl::OO.