Some more tinkering and the interpreter now can calculate "fib 5"; i.e., it has rudimentary operator support now hacked directly into the language. I need to factor out some of it later again.
My operator support scheme is ridiculously slow. I knew that when I designed it but can't say I am happy about it.
I wanted to benchmark the interpreter but that seems difficult since all trivial benchmarks seem to be gone from here. Moreover, the interpreter lacks basic IO routines. Ah well.