[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? [male] yes, the [Inf] examples all work for me. But ... my tclkit(sh)? executables are bit older, some of the first built. [LV] Okay, so I use the base-tcl8.5-thread-solaris-sparc from ActiveTcl 8.5 beta. It says it is patchlevel 8.5a5. And I get the domain error, not the -NaN. ---- See also [expr] - [Inf] ---- [Category Glossary]