Forth in Rust.

FRUSTRATION has got a foot standing on its own tail because writing a monolithic outer interpreter in a high level language makes it really annoying to monkey with the functioning of the interpreter from within the language it's interpreting. PARSE/WORD and the input stream handling was the first place this became obvious. This design is a dead end. The path forward would be stripping it back to primitives and rewriting the outer interpreter in Forth.