Not really I’m afraid. Effects can be anywhere and they are not wrapped at all.

In technical terms it’s stack-oriented meaning the only way for functions (called “words”) to interact with each other is via a parameter stack.

Here’s an example:

: TIMES-10  ( x -- y )
  10 
  * 
;

12
TIMES-10
.S
120

TIMES-10 is a word which pops one parameter from stack and pushes the result of its calculation onto stack. The ( x -- y) is a comment which conventionally documents the “stack effect” of the word.

Now when you type 12 and press RETURN, the integer 12 is pushed onto stack. Then TIMES-10 is called which in turn pushes 10 onto stack and invokes * which pops two values from stack and multiplies them and pushes the result onto stack.

That’s why when type .S to see the contents of the stack, you get 120 in response.

Another example is

5 10 20 - *
.S
50

This simple example demonstrates the reverse Polish notation (RPN) Forth uses. The arithmetic expression is equal to 5 * (20 - 10) the result of which is pushed onto stack.

PS: One of the strengths of Forth is the ability to build a vocabulary (of words) around a particular problem in bottom-to-top fashion, much like Lisp. PPS: If you’re ever interested to learn Forth, Starting Forth is a fantastic resource.

Besides the fun of stretching your mental muscles to think in a different paradigm, Forth is usually used in the embedded devices domain (like that of the earlier Mars rover I forgot the name of).

This project for me is mostly for the excitement and joy I get out of implementing a Forth (which is usually done in Assembler and C) on the JVM. While I managed to keep the semantics the same the underlying machinery is vastly different from, say, GForth. I find this quite a pleasing exercise.

Last but not least, if you like concatenative but were unable to practice fun on the JVM, bjForth may be what you’re looking for.

Hope this answers your question.

Whoa! This is pretty rad! Thanks for sharing!

That’s definitely an interesting idea. Thanks for sharing.

Though it means that someone down the line must have written a bootstrap programme with C/Assembler to run the host forth.

In case of jbForth, I decided to write the bootstrap too.

That’s impossible unless you’ve got a Forth machine.

Where the OS native API is accessible via C API, you’re bound to write, using C/C++/Rust/etc, a small bootstrap programme to then write your Forth on top of. That’s essentially what bjForth is at the moment: the bootstrap using JVM native API.

Currently I’m working on a set of libraries to augment the 80-something words bjForth bootstrap provides. These libraries will be, as you suggested, written in Forth not Java because they can tap into the power of JVM via the abstraction API that bootstrap primitives provide.

Hope this makes sense.

Haha…good point! That said bjForth is still a fully indirect threaded Forth. It’s just that instead of assembler and C/C++ it calls Java API to do its job.