Lisp in Small Processors
While AI is all the rage again, the previous AI wave was focusing on languages like Lisp and Prolog and even built hardware with special processors optimized to execute Lisp code, made by companies such as Symbolics, Lisp Machines, Inc., and the Explorer Series by Texas Instruments. The machines used OSes written in Lisp and provided the user with large, bitmapped screens to operate a mouse-based GUI and networking.
Lisp machines originated at MIT's AI Lab and were influential for a number of reasons. A certain Richard Stallman was a graduate student at the AI Lab and unhappy with the commercialization of the Lisp technology by LMI and Symbolics, started to develop Free Software such as Emacs and the gcc compiler and started the Free Software Foundation. The LMI LAMBDA machine was based on Western Digital's NuBus bus system and was subsequently acquired by TI to create the Explorer.
The NuBus was, in turn, used by Motorola 68k-based Macintosh and early PowerPC systems as well as the NeXT Cube. These NuBus-based Macs were subsequently used to create personal Lisp workstations which employed a VLSI integrated Lisp chip and used the Mac as I/O system. Both Symbolics and TI offered such a system, MacIvory and MicroExplorer, respectively. The latest development is an emulator of Symbolics Lisp machines, the Genera OS.
If you own a MacIvory or MicroExplorer card you want to sell, please get in touch
However, there were also efforts to implement Lisp on smaller machines, including popular 8-bit CPUs. The August 1979 issue of BYTE magazine was dedicated to Lisp and did not only provide a lot of background on the language and its application, but also published the implementation of a Lisp interpreter written by S. Tucker Taft in assembly for the Motorola 6800. Unfortunately, the space in that issue was constrained, so only a part of the interpreter source code was published and the complete code could be ordered from BYTE. 45 years later, this is no longer possible, so I thought the code was lost...
Thanks to the power of Mastodon, Pablo Marx (thanks a lot!) managed to find the original listing of that Lisp implementation and sent me the scanned document as PDF as well as a link to his github repository with the 6800 Lisp code.
If you are interested to know how a low-level implementation of a Lisp VM, including the REPL, lambdas, and a garbage collector works, I can recommend taking a look at this article and the accompanying source code. I'm thinking of porting the VM to my Scopetrex Vectrex game console clone. This is a fascinating piece of hardware based on Motorola's 6809 CPU, the successor of the 6800, which is not binary compatible. However, the assembler source code can be easily converted. The Vectrex and the Scopetrex clone use a vector CRT display, which makes developing software for the system quite interesting.
Automatic conversion of the assembly code should also be possible, e.g. there is a 6502 to 6809 converter.