There has been improvement on this.
Tcl 8.4.16 now allows a 64bit build on OSX. But strangely Tk 8.4.16 still strips out 64bit arch flags.
I found that I could use the ccub trick <http://www.macosxhints.com/article.php?story=20061025213851279 > to fool Tk into building quad-arch Intel+PPC/32+64.
I think the Tcl change is just a start, or maybe unintentional backporting. The same changes are in 8.5, including Tk. When building both Tcl and Tk 8.4.16 64bits, there are a bunch of "cast from pointer to int loses precision" warnings. These are fixed in 8.5.
But, 8.4.16 runs 64bit, despite the cast warnings. GUI seems to work fine.
And NVIZ runs 64bit. But there is a redraw problem (bits of OSX backgrond windows showing, large portions of the window don't redraw) until the window is resized, then redraw is fine. I recall seeing some discussion of a similar (same?) problem, but a couple searches didn't turn up anything in the lists, maybe I didn't pick the right keywords.
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William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
http://www.kyngchaos.com/
"Time is an illusion - lunchtime doubly so."
- Ford Prefect