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Ren-C is a deeply redesigned LGPL 3.0-licensed derivative of the Rebol 3 codebase. It explores solutions to some of the Rebol language's longstanding open questions, adding fundamental new evaluation abilities and API embeddings.

While Rebol 3 built for many platforms, Ren-C extends those to everything from OpenBSD to HaikuOS and WebAssembly. But the experimental nature of the project and limited resources mean there isn't support for packaging and distribution of native binaries. So the table stakes for participating is building your own native interpreter (see instructions below)

The current sole focus for deploying a prebuilt experience to users is via WebAssembly in the web browser. See the demo of the Web Console that was shown at the Rebol 2019 Conference.

(A more conservative evolution of the R3-Alpha codebase is maintained by user @Oldes, and may interest some people who don't want to run on the web.)


One major enabling feature of Ren-C is that it has a "user-friendly" API for C and JavaScript, which uses novel tricks to compose code as mixtures of strings and spliced Rebol values:

int x = 1020;
REBVAL *negate = rebValue("get 'negate");  // runs code, returns value

rebElide("print [", rebI(x), "+ (2 *", negate, "358)]");

// Would print 304--e.g. `1020 + (2 * -358)`, rebElide() returns C void.

The way this can work is described in another talk from Rebol 2019, entitled "Abusing UTF-8 For Fun and Profit"

Beyond the API and Web Build, improvements to the language itself range in the hundreds. They are ever-evolving but are tracked periodically on the Trello board and posts on the forum.


The best way to get acquainted with all that is going on would be to Join The Forum! Feel free to post in the Introductions Category and ask anything you would like.

It's also possible to contact the developers via the GitHub Issues. (Ren-C inherited Rebol's thousands-strong issue database, so there's a lifetime's worth of design points to think about!)


The "Ren-C" name comes from the idea that it is a C implementation of the "REadable Notation" (a name given to Rebol's file format). The codebase is able to compile as ANSI C89, despite using a wide spectrum of static analysis enhancements that apply if built as C++.

Long term, it is not intended to be the name of a language. It's simply a core that could be packaged and configured by other "branded" distributions, such as Rebol itself.


The system does not require GNU Make, CMake, or any other make tools. It only needs a copy of a Ren-C executable to build itself. To do a full build, it can just invoke a C compiler using the CALL facility, with the appropriate command lines.

Several platforms are supported, including Linux, Windows, OS X, Android, and support for JavaScript via WebAssembly. Configurations for each platform are in the %configs/ directory. When the build process is run, you should be in the directory where you want the build products to go (e.g. %build/). Here is a sample of how to compile under Linux:

# You need a Ren-C-based Rebol to use in the make process
# See %tools/bootstrap-shim.r regarding what versions are usable
# Currently there are usable executables in %/prebuilt ...
# ...but that's not a permanent solution!
~/ren-c$ export R3_MAKE="$(pwd)/prebuilt/r3-linux-x64-8994d23"

~/ren-c$ cd build

~/ren-c/build/$ "$R3_MAKE" ../make.r \
    config: ../configs/default-config.r \
    debug: asserts \
    optimize: 2

For a list of options, run %make.r with --help.

Though it does not require other make tools, it is optional to generate a makefile target, or a Visual Studio solution. %make.r takes parameters like target: makefile or target: vs2017. But there are several complicating factors related to incremental builds, due to the fact that there's a large amount of C code and header files generated from tables and scans of the source code. If you're not familiar with the source and what kinds of changes require rebuilding which parts, you should probably do full builds.

As a design goal, compiling Ren-C requires very little beyond ANSI C89. Attempts to rein in compiler dependencies have been a large amount of work, and it still supports a number of older platforms. However, if it is compiled with a C++ compiler then there is significantly more static analysis at build time, to catch errors.

(Note: The build process is much more complicated than it should be, but other priorities mean it isn't getting the attention it deserves. It would be strongly desirable if community member(s) could get involved to help streamline and document it! Since it's now all written in Rebol, that should be more possible--and maybe even a little "fun" (?))


When Rebol was open-sourced in 2012, it was licensed as Apache 2.0. Despite the Ren-C team's belief in Free Software Foundation's principles, contributions were made as Apache 2.0 up until 2020, to make it easier for code to be taken back to the Rebol GitHub or other branches.

Due to limited cases of such any take over an eight-year span, the Ren-C license was changed to the Apache-2-compatible LGPL 3.

The current way to explore the new features of Ren-C is using the r3 console. It is significantly enhanced from the open-sourced R3-Alpha...with much of its behavior coming from userspace Rebol code (as opposed to hardcoded C). In addition to multi-line editing and UTF-8 support, it can be "skinned" and configured in various ways, and non-C programmers can easily help contribute to enhancing it.


Library for embedding a Rebol interpreter into C codebases








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