[AMG]: In Tcl, each value's data type is implicitly determined by the operations performed on the value.  This is called "duck typing" [http://en.wikipedia.org/wiki/Duck_typing].

===
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             ;# $data is an [expr]ession
expr {$data}           ;# $data is an [integer]
regexp $data 4242      ;# $data is a [regexp]
set data [expr 99]     ;# $data is an integer
string length $data    ;# $data is a string
===

and so on.

Beware of [shimmering]!

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