[microtherion]

That's how I did it in 1983 (but I think with the roles for S and U swapped).

Note that what you're describing is directly threaded code; traditional FORTH uses indirect threaded code: http://www.complang.tuwien.ac.at/forth/threaded-code.html

[dwgumby]

You're right, I forgot the indirection. Inner Interpreter instruction is actually: JMP [,y++]