[monetus]

There are these pages on the wiki regarding closures, and a reference to needing to change the internals of tcl_ObjType in order to implement them.

https://wiki.tcl-lang.org/page/Closures

https://wiki.tcl-lang.org/page/Emulating+closures+in+Tcl

TCL 9 has surely fiddled with tcl_ObjType I hope, but it doesn't seem like it from a glance.