alt Hacker News > Well, I've encountered this use case a few times in Lisp:...
> ...where a callback is used to collect various items.
Despite that, I find article interesting. It shows that Tcl can truely be multiparadigm programming language.
Myself, I've implemented pattern matching [1] over algebraic-type-like values and used that here and there.
The callback way is more generic and prevents consing when you don't need to store the resulting node list. You may want to simply print something or maybe modify the node in-place, for example.