PCR (Portable Common Runtime") from PARC was a reimplementation of the runtime that Cedar and Mesa and even a PostScript interpreter used, so they could be ported to run on Unix (Sun SPARC and maybe 68k). It included the Bohem/Weiser garbage collector, among other stuff.

That's what Eric Bier was demonstrating in the Computer History Museum Cedar Demonstration video I linked to below. I've written more about PCR before:

https://news.ycombinator.com/item?id=22456720

>So there was an ongoing discussion about the best way to do it all over again from scratch. Scheme was obviously an excellent language to use instead of PostScript. Here are some notes from February of 1990 (before the abomination that is CORBA was thrust upon the world), discussing how to apply John Warnock's "linguistic motherboard" ideas to other languages like Scheme, and how to implement them on top of something like Xerox PARC's "PCR" (Portable Common Runtime, essentially the virtual operating system runtime that Cedar and other Xerox software like Interpress required to run on other platforms like Unix).

>(But first here's some other stuff I wrote recently about Cedar and PCR, for context. And I've inserted some links into the notes.)

>[...]

https://news.ycombinator.com/item?id=34056973

>You know what's a lot like Ada in a good way is Mesa, which evolved into Ceder, from Xerox PARC. I know people who really loved programming in it. They'd call it "Industrial Strength Pascal". It was a successful experiment in code reuse. A strongly typed language with strong separation between interfaces and implementations, which encouraged creating robust, hardened code.

https://en.wikipedia.org/wiki/Mesa_(programming_language)

>Mesa and Cedar had a major influence on the design of other important languages, such as Modula-2 and Java, and was an important vehicle for the development and dissemination of the fundamentals of GUIs, networked environments, and the other advances Xerox contributed to the field of computer science.

Demonstration of the Xerox PARC Cedar integrated environment (2019) [video] (youtube.com)

https://news.ycombinator.com/item?id=22375449

Computer History Museum: Eric Bier Demonstrates Cedar

https://www.youtube.com/watch?v=z_dt7NG38V4

>Mark Weiser and others at Xerox PARC's ported the Cedar environment to Unix, which resulted in the development of the still-widely-used Boehm–Demers–Weiser conservative garbage collection.

https://news.ycombinator.com/item?id=22378457

>I believe that stuff is the port of Cedar to the Sun. Xerox PARC developed "Portable Common Runtime", which was basically the Cedar operating system runtime, on top of SunOS (1987 era SunOS, not Solaris, so no shared libraries or threads, which PCR had to provide). He demonstrates compiling a "Hello World" Cedar shell command, and (magically behind the scenes) dynamically linking it into the running shell and invoking it.

>Experiences Creating a Portable Cedar.

Russ Atkinson, Alan Demers, Carl Hauser, Christian Jacobi, Peter Kessler, and Mark Weiser.

CSL-89-8 June 1989 [P89-00DD6]

http://www.bitsavers.org/pdf/xerox/parc/techReports/CSL-89-8...

>>Abstract: Cedar is the name for both a language and an environment in use in the Computer Science Laboratory at Xerox PARC since 1980. The Cedar language is a superset of Mesa, the major additions being garbage collection and runtime types. Neither the language nor the environment was originally intended to be portable, and for many years ran only on D-machines at PARC and a few other locations in Xerox. We recently re-implemented the language to make it portable across many different architectures. Our strategy was, first, to use machine dependent C code as an intermediate language, second, to create a language-independent layer known as the Portable Common Runtime, and third, to write a relatively large amount of Cedar-specific runtime code in a subset of Cedar itself. By treating C as an intermediate code we are able to achieve reasonably fast compilation, very good eventual machine code, and all with relatively small programmer effort. Because Cedar is a much richer language than C, there were numerous issues to resolve in performing an efficient translation and in providing reasonable debugging. These strategies will be of use to many other porters of high-level languages who may wish to use C as an assembler language without giving up either ease of debugging or high performance. We present a brief description of the Cedar language, our portability strategy for the compiler and runtime, our manner of making connections to other languages and the Unix operating system, and some measures of the performance of our "Portable Cedar".

>PCR implemented threads in user space as virtual lightweight processes on SunOS by running several heavy weight Unix processes memory mapping the same main memory. And it also supported garbage collection. Mark Weiser worked on both PCR and the Boehm–Demers–Weiser garbage collector.

https://en.wikipedia.org/wiki/Boehm_garbage_collector

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