True or False. Tcl has no separate Boolean type, like in C, the integers 0 (false) and 1 (true - in fact any nonzero integer) are used.

[NEM]: Although [expr] will also accept "true" and "false" (and "yes"/"no"..) as Boolean
values.

[1S]
In fact, there's no separate Integer type in [Tcl] as well -- everything
is a string.  A proper boolean value is either a proper integer, with,
like in [C], zero meaning false and non-zero meaning true, or one of the
following: '''yes''', '''no''', '''true''', '''false''', '''on''', or
'''off'''.

[RS] The canonical forms however, like [expr] produces them, are 1 and 0.

See [Boolean Logic] or [Integers as Boolean Functions].

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[HaO] Since TCL8.5, expr knows the '''bool()''' function to bring strings in boolean canonical form.
This is quite handy to use '''==''' or '''!=''' on booleans in different form:
======
% expr {bool(true) == bool(1)}
1
======

'''==''' does not work for arbitrary booleans:
======
% expr {true == 1}
0
======

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[[ [Category Glossary] ]]