More Forth
The Forth programming language is a thing I’ve previously written about. I recently came across this little gem of a talk, wherein the author points to some interesting resources about Forth. In particular, the slides put emphasis on how minimal a Forth implementation can be.
The point about Forth is that it heavily depends on threaded code. That’s a simple technique to implement an interpreter on the bare metal. In a nutshell, code to be executed by a threaded interpreter is mostly addresses of implementations of logic, that the very simple interpreter “loop” just loads and jumps to, following a “thread” of addresses through its implementation.
Indeed, Forth source code consists of just “words” that are concatenated to express semantics. These human-readable words are mere placeholders for the memory addresses where the words' implementations can be found. In other words, a Forth compiler is simplistic: it boils down to dictionary lookups.
To demonstrate the minimalism, the PlanckForth interpreter is just a 1 kB hand-written ELF binary. The syntax of the basic language this interpreter understands is a bit awkward, but sufficiently powerful to bootstrap a full-fledged Forth in just a couple hundred lines.
JonesForth is a richly documented Forth implementation. (You’ll have to go through the snapshot link to get the source code.) Reading the code is highly instructive.
Tags: the-nerdy-bit, hacking