This reminds me of a technique I learned from this StackOverflow answer [1] that is about creating structs/records with TCL lists and dicts. It apparently come

This reminds me of a technique I learned from this StackOverflow answer [1] that is about creating structs/records with TCL lists and dicts. It apparently comes from LISP philosophy: proc mkFooBarRecord {foo bar} { # Keep index #0 for a "type" for easier debugging return [list "fooBarRecord" $foo $bar] } proc getFoo {fooBarRecord} { if {[lindex $fooBarRecord 0] ne "fooBarRecord"} {error "not fooBarRecord"} return [lindex $fooBarRecord 1] } The magic number is sort of like the "0" index of the "Type" field with dicts. field. [1] https://stackoverflow.com/a/5532898 https://stackoverflow.com/a/5532898