stoneknifeforth VS able-forth

a problem that a lot of these series run into is that the author runs out of steam before they finish writing them. crenshaw's otherwise excellent series suffers from this, for example

so far the author of this one has only written the first chapter

i've written a few didactic compilers that are complete enough to compile themselves, though nothing else

https://github.com/kragen/stoneknifeforth (from a forth-like language to an i386 linux elf executable)

https://github.com/kragen/peg-bootstrap/blob/master/peg.md (from a peg language description with semantic actions to javascript)

http://canonical.org/~kragen/sw/urscheme (from a subset of scheme to at&t-syntax i386 assembly)

Look at how much room you have for data! I wonder what we can fit in there.

More seriously, a metacircular example to draw from would be: https://github.com/kragen/stoneknifeforth

i wasn't able to get a runnable forth to less than a couple of pages written in itself https://github.com/kragen/stoneknifeforth but schönfinkel's ski-combinators are maybe the simplest practical basis

    s f g x → f x (g x)

I've done all these things (except designing the hardware) and I agree that it can be very painful. I did some of them in 02008, for example: https://github.com/kragen/stoneknifeforth

The thing is, though, you can also not do all those things. You can use variables, and they don't even have to be allocated on a stack (unless you're writing a recursive function, which you usually aren't), and all the NIP TUCK ROT goes away, and with it all the Memory Championship tricks. You can test each definition interactively as you write it, and then the fact that the language is absurdly error-prone hardly matters. You can use metaprogramming so that your code is as DRY as a nun's pochola. You can use the interactivity of Forth to quickly validate your hypotheses about not just your code but also the hardware in a way you can't do with C. You can do it with GDB, but Forth is a lot faster than GDBscript, but that's not saying much because even Bash is a lot faster than GDBscript.

But Yossi was just using Forth as a programming language, like a C without local variables or type checking, not an embedded operating system. And, as I said, that's really not Forth's strength. Bash and Tcl aren't good programming languages, either. If you try to use Tcl as a substitute for C you will also be very sad. But the way they're used, that isn't that important.

I explained a more limited version of this 12 years ago: https://yosefk.com/blog/my-history-with-forth-stack-machines...

So, I don't think Forth is only useful when you have the freedom to change the problem, though programs in any language do become an awful lot easier when you have that freedom.

That's powerful enough to conveniently write, for example, a numerical root finding program for an arbitrary arithmetic expression.

But I think that within a complexity budget of 150 lines of code you can maybe be even more ambitious than that.

The example compiler in https://github.com/darius/parson/blob/master/eg_calc_compile... is a bit more stripped down than that, but in its 32 lines of code it compiles arithmetic assignment statements to a three-address RISC-like code (though using an unbounded number of registers). https://github.com/darius/parson/blob/master/eg_calc_to_rpn.... is a 16-line version that compiles the same language to a stack machine like your tutorial example.

In 66 lines of code in https://github.com/kragen/peg-bootstrap/blob/master/peg.md I wrote an example compiler which compiles a PEG grammar into a JavaScript parser for that grammar. Admittedly those 66 lines do not include an implementation of JavaScript to run the code on. It compiles the language it's written in.

In 132 lines of code in https://github.com/kragen/stoneknifeforth/blob/master/tinybo... I wrote an example compiler which compiles a crippled Forth dialect into i386 machine code, including an ELF header so you can run the result. It also compiles the language it's written in. It also doesn't include an i386 emulator to run it on.

In 83 lines of code in http://canonical.org/~kragen/sw/dev3/neelcompiler.ml Neel Krishnaswami wrote a compiler from the untyped λ-calculus to a simple assembly language for a register machine. It also doesn't include an implementation of the assembly language.

In 18 lines of code in http://canonical.org/~kragen/sw/dev3/meta5ix.m5, a simplification of META-II, I wrote a compiler from grammar descriptions to an assembly code for a parsing-oriented virtual machine. It compiles the language it's written in. A Python interpreter for the machine is in http://canonical.org/~kragen/sw/dev3/meta5ixrun.py (109 lines of code) and a precompiled version of the compiler-compiler for bootstrapping is in http://canonical.org/~kragen/sw/dev3/meta5ix.generated.m5asm.

A slightly incompatible variant of Meta5ix which instead compiles itself to C is in http://canonical.org/~kragen/sw/dev3/meta5ix2c.m5 (133 lines of code, depending on how you count). (No C compiler is included.) The precompiled C output for bootstrapping is in http://canonical.org/~kragen/sw/dev3/meta5ix2c.c.

Meta5ix is extremely weak and limited, really only enough for a compiler front-end; it can't, for example, do the kinds of RPN tricks we're talking about above.

Title effectively says it all. The only thing I have found is StoneKnife Forth (implementation is in tinyboot1.tbf1) but this file is implemented in the same dialect of forth it implements, which due to being minimal makes it difficult to read and comprehend efficiently (I also can't find the origin of some words such as 'byte' used in the code but not implemented by the interpreter). I would prefer something in the C family to look at but anything should do as long as it's clean enough that I could use it as a reference to reimplement the compiler without much difficulty. Thank you in advance for any help with what is seemingly quite a narrow request.

I'm pretty sure Linux ELF has always allowed you to specify the initial load address. When I first wrote StoneKnifeForth https://github.com/kragen/stoneknifeforth its load address was 0x1000, but at some point Linux stopped allowing load addresses lower than 0x10000 by default (vm.mmap_min_addr). I originally wrote it in 02008, using the lower load address, and fixed it in 02017. It's still not using 0x804800 like normal executables but 0x20000. ASLR does not affect this.

Maybe you mean that before ELF support, Linux a.out executables had to be loaded at a fixed virtual address? That's possible—I started using Linux daily in 01995, at which point a.out was already only supported for backward compatibility.

This is more advanced than the common Forth struct implementation example but this is real Able Forth code used at Merj. The Able Forth code above gives you first-class types, vectors and records, and type extension (like inheritance). These words are the basis for other types.

Able Forth Optimized \ (smart postpone). Timed-wait is now available! The new now instruction provides access to a real-time nanosecond precision clock that is suitable for many tasks, including performance profiling. The default exception handler is now easy to replace at runtime.

Able Forth The bootstrap process is fully automated and easy to customize, making it simpler than ever to create a custom Forth system. A new create does implementation inspired by cmForth. A defer is implementation that more closely follows the standard. A smarter alias implementation guarantees aliases behave as expected in all cases. depth and reset instructions for retrieving stack depths and resetting execution. All signalled exceptions are trapped and reported by default.

Of course, there are many more use-cases. What surprised me is how simple it is to implement unwind protect in Forth (here implemented in Able Forth) and that I've never seen it implemented before :-).

I would consider adding Able Forth to the list. The Able Forth compiler targets the AbleVM, but in every other respect, it's a native code compiler (there's no reason Able Forth couldn't be made to emit native code for a physical machine). The default AbleVM core was designed to make the Able Forth compiler simple; it implements a 0-operand dual-stack virtual machine with ample general-purpose and base+offset address registers. Able is open source, in production use and under active development. If you decide it's interesting and you have any questions we're here to help.

While not exactly that, Able Forth works this way; more for simplicity than for efficiency. In Able Forth, there is no separate interpreter. Code entered to be executed immediately -- what we call evaluated -- is compiled into an evaluation buffer and a dynamic call is to the beginning of this buffer is performed. Primitives are implemented as compiling words that emit their required instructions, meaning that the code generated will be executed at full speed.