Parable is a small language, built over a compact byte coded virtual
machine. The language uses a concatenative model with a strictly
reverse polish notation, type awareness, and garbage collection.
The syntax draws from earlier work on Toka and Retro, making extensive
use of anonymous, nestable functions (called quotations) for function
definition and control structures. The language also depends heavily
on prefixes to help the compiler decide how to handle tokens. (These
are a lot like colors in ColorForth, but are represented as single
characters rather than color or stylistic elements).
One other major difference from my earlier work is the memory model.
Parable divides memory into distinct regions called slices. Memory
accesses are done by referencing a slice and an offset. This differs
from Retro and Toka which both used a single linear memory area for
all code and data. The use of slices has allowed for some interesting
things, including a garbage collector, and much simpler decompilation
back to readable source code.
The core language does not provide a specified I/O model. This is
intentional; I now work with a variety of platforms and languages, and
enforcing the existence of a traditional console environment has
proven to be a limiting factor. Parable frees me to implement custom
I/O functionality on a per-application basis, through the use of
custom byte code additions. I have written numerous interfaces,
including a simple script interpreter, an interactive full screen
REPL, a browser based interface, and an implementation for iOS. There
is also a console script interpreter with support for file I/O, basic
output and command line argument support.
"Return a string containing 'hello world'"
"Average some values"
[ 1 3 5 7 9 ] slice-length? [ 0 [ + ] reduce ] dip /
January 2017 Update:
It's been several months since I have worked on Parable. Sadly it has
failed to gain any real traction and has only a few users. It's not
dead though. I still have some things using it, and intend to make
further improvements to the language later this year.
forthworks.com:80 / atua-www / running on retro