While issue 314 (http://d.puremagic.com/issues/show_bug.cgi?id=314) is still open, we can't make selective imports in phobos modules, as they become public imports.

Besides, isnan is only ever used in two specific (and templated) functions, so it should be better to just scope the imports to the body of those functions no? IF the user never actually prints a floating point, he won't import the the module.