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> Developers from Fuji Xerox wrote a portable VM in C to run the environment on different host platforms, called Maiko. I'm always confused by the relationship

by uticus 3y ago

> Developers from Fuji Xerox wrote a portable VM in C to run the environment on different host platforms, called Maiko. I'm always confused by the relationship of C and Lisp(s). Here the VM is written in C. Yet elsewhere there seem to be at least one good example of a Lisp compiler written in Lisp [0]. What was the reason for writing Maiko in C, versus Lisp "all the way"? [0] "The first complete Lisp compiler, written in Lisp, was implemented in 1962 by Tim Hart and Mike Levin at MIT, and could be compiled by simply having an existing LISP interpreter interpret the compiler code, producing machine code output able to be executed at a 40-fold improvement in speed over that of the interpreter.[19] This compiler introduced the Lisp model of incremental compilation, in which compiled and interpreted functions can intermix freely. The language used in Hart and Levin's memo is much closer to modern Lisp style than McCarthy's earlier code. " https://en.wikipedia.org/wiki/Lisp_(programming_language)#History https://en.wikipedia.org/wiki/Lisp_(programming_language)#Hi...

5- 3y ago
it'd be entirely possible to write the vm in lisp (there are plenty of good optimising lisp compilers, e.g. sbcl). however, typically you'd want the vm to be easily portable / buildable in new environments, and that's much easier to achieve with c. and it is likely just easier to write this kind of low-level code in c (however i know plenty of people who will gladly demonstrate otherwise). consider that the jvm et al are also written in c(++), for much the same reasons of practicality.
- gumby 3y ago
  The C abstract machine is basically an overgrown PDP-11 at this point and most modern hardware is designed with that in mind with GPU and vector hardware being notable exceptions — and notably not being especially amenable to programming in C. It’s actually been an unfortunate and pernicious codependence IMHO.
lispm 3y ago
A Lisp and a compiler are two different things: Lisp is the whole thing and the Lisp compiler is just a component of a Lisp system. Now, one could write a virtual machine in Lisp, but usually one would write it in C or assembler, since that's what squeezes more performance out of the hardware and makes interfacing to the operating system 'easier' (threads, calls into the OS, memory management, interrupts, error handling, etc.). There are examples where (parts of) a virtual machine are written in Lisp. For example the Virtual-CPU emulator may be generated as C or assembler code from a Lisp program. There are also special versions of, say, the JVM written in Lisp to prove its correctness. Ideally one may want to have the core VM emulator written in assembler to reduce it to the most minimum hardware instructions per virtual machine instruction. The example you cited from 1962 is a Lisp compiler written in Lisp, compiled by itself, running in a Lisp whose runtime was written in assembler (IIRC).
- uticus 3y ago
  That helps, thank you. Based on what I've seen with Smalltalk, and playing around with the online Interlisp environment [0], I was under the impression an underlying OS was not a necessity [1]. [0] https://online.interlisp.org/main https://online.interlisp.org/main [1] Part of my confusion may stem from ideas like presented by Chuck Moore in Masterminds of Programming by Biancuzzi: "Operating systems are dauntingly complex and totally unnecessary. It’s a brilliant thing that Bill Gates has done in selling the world on the notion of operating systems. It’s probably the greatest con game the world has ever seen. An operating system does absolutely nothing for you. As long as you had something—a subroutine called disk driver, a subroutine called some kind of communication support, in the modern world, it doesn’t do anything else. In fact, Windows spends a lot of time with overlays and disk management all [sic] stuff like that which are irrelevant. You’ve got gigabyte disks; you’ve got megabyte RAMs. The world has changed in a way that renders the operating system unnecessary. What about device support? Chuck: You have a subroutine for each device. That’s a library, not an operating system. Call the ones you need or load the ones you need."
  - lispm 3y ago
    http://lispm.de/genera-concepts http://lispm.de/genera-concepts
    - uticus 3y ago
      Fascinating. > Genera is your whole environment; it encompasses what you normally think of as an operating system as well as everything else - system commands and all other activities. From where you look at it, there is no "top-level" controller or exec.
      - lispm 3y ago
        But it has a sophisticated process scheduler, several garbage collectors, complex memory management, various network stacks, implementations of file systems (local and remote), virtual memory paging, software installer, printer scheduler, namespace server for configuration of networked resources (users, networks, printers, hosts, ...), mail server and client, ... It's not that it has "a subroutine" for a disk, but actually very extensive support for disks and file systems on disk. It's just that everything runs in one spared memory space, incl. all applications. Probably not a winning way to design a networked OS in today's Internet environment.
rmckayfleming 3y ago
It's more that it's easier to use C for two reasons. The first is that C is really popular and therefore pretty portable. It's a lingua franca. The other is that because the hosts are largely defined in C, it's easier to interact with. Of course, the host doesn't actually "speak C", it follows some form of ABI. But the reality is that implementing each ABI is non-trivial and you can avoid a lot of pain by just using the host's C compiler/linker/etc. that implements it for you.
- rmckayfleming 3y ago
  Like, SBCL compiles and assembles directly to machine code, that's very much the Lisp way. But SBCL has a lot of C that's involved in getting the SBCL image running and interacting with the host.

by uticus 3y ago

5- 3y ago

it'd be entirely possible to write the vm in lisp (there are plenty of good optimising lisp compilers, e.g. sbcl). however, typically you'd want the vm to be easily portable / buildable in new environments, and that's much easier to achieve with c. and it is likely just easier to write this kind of low-level code in c (however i know plenty of people who will gladly demonstrate otherwise). consider that the jvm et al are also written in c(++), for much the same reasons of practicality.

gumby 3y ago
The C abstract machine is basically an overgrown PDP-11 at this point and most modern hardware is designed with that in mind with GPU and vector hardware being notable exceptions — and notably not being especially amenable to programming in C. It’s actually been an unfortunate and pernicious codependence IMHO.

lispm 3y ago

A Lisp and a compiler are two different things: Lisp is the whole thing and the Lisp compiler is just a component of a Lisp system. Now, one could write a virtual machine in Lisp, but usually one would write it in C or assembler, since that's what squeezes more performance out of the hardware and makes interfacing to the operating system 'easier' (threads, calls into the OS, memory management, interrupts, error handling, etc.). There are examples where (parts of) a virtual machine are written in Lisp. For example the Virtual-CPU emulator may be generated as C or assembler code from a Lisp program. There are also special versions of, say, the JVM written in Lisp to prove its correctness. Ideally one may want to have the core VM emulator written in assembler to reduce it to the most minimum hardware instructions per virtual machine instruction. The example you cited from 1962 is a Lisp compiler written in Lisp, compiled by itself, running in a Lisp whose runtime was written in assembler (IIRC).

uticus 3y ago
That helps, thank you. Based on what I've seen with Smalltalk, and playing around with the online Interlisp environment [0], I was under the impression an underlying OS was not a necessity [1]. [0] https://online.interlisp.org/main https://online.interlisp.org/main [1] Part of my confusion may stem from ideas like presented by Chuck Moore in Masterminds of Programming by Biancuzzi: "Operating systems are dauntingly complex and totally unnecessary. It’s a brilliant thing that Bill Gates has done in selling the world on the notion of operating systems. It’s probably the greatest con game the world has ever seen. An operating system does absolutely nothing for you. As long as you had something—a subroutine called disk driver, a subroutine called some kind of communication support, in the modern world, it doesn’t do anything else. In fact, Windows spends a lot of time with overlays and disk management all [sic] stuff like that which are irrelevant. You’ve got gigabyte disks; you’ve got megabyte RAMs. The world has changed in a way that renders the operating system unnecessary. What about device support? Chuck: You have a subroutine for each device. That’s a library, not an operating system. Call the ones you need or load the ones you need."
- lispm 3y ago
  http://lispm.de/genera-concepts http://lispm.de/genera-concepts
  - uticus 3y ago
    Fascinating. > Genera is your whole environment; it encompasses what you normally think of as an operating system as well as everything else - system commands and all other activities. From where you look at it, there is no "top-level" controller or exec.
    - lispm 3y ago
      But it has a sophisticated process scheduler, several garbage collectors, complex memory management, various network stacks, implementations of file systems (local and remote), virtual memory paging, software installer, printer scheduler, namespace server for configuration of networked resources (users, networks, printers, hosts, ...), mail server and client, ... It's not that it has "a subroutine" for a disk, but actually very extensive support for disks and file systems on disk. It's just that everything runs in one spared memory space, incl. all applications. Probably not a winning way to design a networked OS in today's Internet environment.

rmckayfleming 3y ago

It's more that it's easier to use C for two reasons. The first is that C is really popular and therefore pretty portable. It's a lingua franca. The other is that because the hosts are largely defined in C, it's easier to interact with. Of course, the host doesn't actually "speak C", it follows some form of ABI. But the reality is that implementing each ABI is non-trivial and you can avoid a lot of pain by just using the host's C compiler/linker/etc. that implements it for you.

rmckayfleming 3y ago
Like, SBCL compiles and assembles directly to machine code, that's very much the Lisp way. But SBCL has a lot of C that's involved in getting the SBCL image running and interacting with the host.