All in tcl is string, so expr exist as command to evaluate numeric value. On other language like ruby if we write 1+2 <enter> on the irb console will print 3, but thats not the case with tcl.
To get numeric calculation on Tcl we need to use expr command.
Evaluating logical also work with expr command. Examples below.
By remembering Tcl rule : “All is string”, we can conclude that expr result will be string as well.