KBK closed a follow-up to [the comp.lang.tcl newsgroup with the advice that, "Also, it's important always, always to brace your expressions. Don't do
set a [expr $b / $c]
but rather
set a [expr { $b / $c }]
Otherwise, your variables may undergo unexpected conversions numeric -> string -> numeric, you can lose precision, your expressions will be much slower, and you can even have security problems:
# don't run set x { [format C:\] } set y [expr $x + 3]
"