Using a new high-level programming language to implement an old low-level language is a strange thing to do, but I've done just that. SuwaneeForth is an implementation of Forth interpreter, written in Swift. If you are interested in such a thing, you can find it here:
SuwaneeForth is a translation/port of the system described in "A sometimes minimal FORTH compiler and tutorial for Linux/i386 systems" (a.k.a. "JONESFORTH") by Richard W.M. Jones. I'd suggest that all programmers read the source to that, as it is a very readable tutorial for bootstrapping a programming language implementation.
I heartily agree with the first paragraph of jonesforth.S:
FORTH is one of those alien languages which most working programmers regard in the same way as Haskell, LISP, and so on. Something so strange that they'd rather any thoughts of it just go away so they can get on with writing this paying code. But that's wrong and if you care at all about programming then you should at least understand all these languages, even if you will never use them.