Compiling OS-X Apps on GNUStep/Linux

Hello

I remember I read somewhere that's Apple Mail program has been
compiled succesfully under Linux/GNUStep. I know there is GNUmail now,
but my question is more, about the compilation.... did I miss read ?
is it really possible to compile a OS-X app under GNUStep ?

what in the code would make the compilation fail ? 
call to the core os-x api ? quartz ? aqua ?

I'd like to get macromates poeple to try to compil under gnustep their
excellent text editor called textmates. if only that could work.

thanks for all the info.


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