[Replace this comment with an explanation of the return value of NaN that occasionally occurs within Tcl]
RS 2007-02-23: NaN is "Not a Number", a sort-of valid floating point value from Tcl 8.5. Here's experiments:
(bin) 13 % set y [expr sqrt(-1)] -NaN (bin) 14 % expr {$y == $y} ;# the only value that is not equal to itself :^) 0 (bin) 15 % expr {$y eq $y} 1
male 2007-02-23: Sorry, but using tclkit(sh)? 8.5a4 ...
% expr {sqrt(-1)} domain error: argument not in valid range
RS I used tclkit 8.5a4 as well, on Win XP. So the patchlevel doesn't yet tell the full story :( Do the Inf examples work for you?