Sat Aug 22 10:40:14 CEST 2009

The return stack should contain XTs

Something that has always bothered me about Forth is that the return
stack contains _pointers_ to XTs (i.e. XT _arrays) while `execute'
takes XTs.

In other word: the return stack _itself_ is not a program.  This is a
consequence of having two forms of code: threaded code and machine
code.  An XT is often implemented as a pointer to machine code (direct
threaded) or a pointer to a pointer to machine code (indirect