The key point, at least for me, is that ifplatform has to work with older distributions. At least for MiKTeX users there is no sign of LuaTeX at the moment, so it will be some time before “just use Lua” is a general option.

Joseph

The os library has a few extra functions and variables:
…

* os.type This is a string that gives a global indication of the class of operating system. The possible values are currently windows, unix, and msdos (you are unlikely to find this value ‘in the wild’).

* os.name This is a string that gives a more precise indication of the operating system. These possible values are not yet fixed, and for os.type values windows and msdos, the os.name values are simply windows and msdos

The list for the type unix is more precise: linux, freebsd, openbsd, solaris, sunos (pre-solaris), hpux, irix, macosx, bsd (unknown, but bsd-like), sysv (unknown, but sysv-like), generic (unknown).

(os.version is planned as a future extension)

So, if you want to call luatex through shell escape, you can create a tex that writes os.name to a text file, process it through luatex, and read the result.

\immediate\write18{echo \ip@win > “\ip@file”}

Unfortunately I don’t have of an opportunity to test with a Windows TeX Live installation. I wonder if LuaTeX would provide a more robust solution to this problem (i.e., calling LuaTeX through shell escape, not requiring LuaTeX for the ifplatform package).