AMG: In Tcl, each value's data type is implicitly determined by the operations performed on the value. This is called "duck typing" [L1 ].
set data {1 2 3 4} ;# $data is a string
llength $data ;# $data is a list
dict size $data ;# $data is a dict
set data 42 ;# $data is a string
expr $data ;# $data is an expression
expr {$data} ;# $data is an integer
regexp $data 4242 ;# $data is a regexpand so on.
Beware of shimmering!