Also, in 8.6 (and later) the C stack and the Tcl stack are not closely
related at all. That's the real core of what the NRE execution engine
does, meaning that Tcl stacks can be managed in much more interesting
ways, but it does make debugging from inside C rather more difficult
(not that it was ever easy, as procedure implementations didn't say
which procedure they were inside 'bt', but the clues were fairly easy to
follow, especially before 8.0).
Donal.
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Donal Fellows — Tcl user, Tcl maintainer, TIP editor.