Levels of code in Forth programing

Levels of code in Forth programing

Levels
of code in Forth programming

I had been programming in Fortran and assembler for a number of years
when I got my first personal computer. It was exciting.
On the first generation PC one had to
toggle in a paper tape loader from front panel switches, byte by byte,
then start the paper tape reader and then one could output to the led
on the front panel. I had waited for the
first model that booted from ROM, had a parallel port for keyboard
input and had video output from he factory, it was 1974.
The PC I got had a wonderful monitor program
that replaced a front panel with a nice video display of the contents
of all the CPU registers where one could change anything and single-step
through programs seeing everything visualized before you. One could also
the video for text and graphics display by your programs.

I found it very educational. About a year later I upgraded from 1KB
of RAM to 9KB and could now run an assembler or BASIC interpreter/editor
on the 8080. There was DOS but I could not afford a disk and used cassette
storage. I also found FIG-FORTH about that time. Since I had assembler
training I found that Forth let me do everything I could in assembler
and much more and do it much faster and re-use my old code that I had compiled
and added to the dictionary in my-language.

I started with voice and speaker recognition, voice output, and then
I added graphics and sound and 3D visualization with interactive
simulations of objects and access to the sub-logic/MS 3D databases
extensions to FIG-FORTH and sold my first system to NASA. I found
porting the whole environment fairly trivial from a cassette based
environment on 8080 to a better graphic and sound environment on
6502 with block based disk I/O access. I had been using Forth quite
a bit now and starting to learn more about it.

My Forth code was carefully layered. I had actually modified the
ROMs on my first machine to default into loading Forth. I had
access from the ROMs on up. I could use ROM code from RAM or write
my own CODE (assembler) words in Forth to form the lowest level of
software above the hardware. I had a layer of code of this type
for the registers, memory, and I/O ports. In some cases there was
a layer of code to define a serial port or other abstracted device
on some parallel port pins using a timer or something. Then there
was a layer of code to provide abstracted control over all the
abstracted hardware and software devices. A layer for the Forth
kernel, a layer for the high level Forth extensions, a layer
for my 3D and sound and voice and object, and finally of course
any application layer on top of this that I could save as a stand-alone
system. This seemed to fit with the evolving ideas in telecommunications
standards providing portable levels or layers.

I was deeply influenced by my first exposure to Smalltalk. At that time my
idea of an ideal environment was a Forth with Smalltalk-like object, graphic,
and GUI extensions. It ultimately wanted to have a source browser
assisted the user in tasks like metacompilation making them almost
transparent. I did add a layer for a Smalltalk-like GUI toolkit
to my Forth dictionary. It only adds a few K at most.

In the eighties I worked in telecommunications and I added appropriate
telecom protocol layers into the system and support for new modems,
and a scripting language layer, and of course scripts. I was also
researching AI in Forth, implementing ideas from LISP examples and
doing expert systems and neural nets and mixing them and building
robots. In the software I added
a layer for an inference engine for English language descriptions of
rule sets and a layer for the rules. I wrote a learning email report
and conversation engine AI program and had it running for a few
months. My boss could not distinguish it from me. That was my idea
of AI, smart enough to do my job for me and get paid at my salary
while I took a vacation.
A couple of years later I purchased
a Forth kit with the first Forth chip and got personal friendly
support from Charles Moore. My ideal language now needed to have
neural and rule based background tasks intelligently cooking
knowledge bases. I also studied parallel programming paradigms and
worked on parallel programming extensions to Forth. [Fox, 1991] [Fox, 1995]
My idealized environment
became a simple and fast parallel Forth chip optimized for AI code and
multimedia and an integrated version of all my Forth code. [Fox, 1993]

Now to jump ahead ten years, I found myself working with Charles Moore,
the inventor of Forth, on our latest custom VLSI. It was be his
fifth generation Forth chip, my first. I had worked with several
of the earlier generations of chips but not contributed to or owned
a license on the design as with the F21.

Working closely with him for a number of years changed most of my
ideas about Forth. I thought I knew Forth by this time and was somewhat
perplexed by what I saw Chuck do. I still could not get close to the results
that he got, either in productivity or quality. I tried very hard to
study and understand what he was doing different than the Forth
that I had learned. I recall that the first thing that jumped out at me
was that Chuck’s code didn’t have all those layers that my code had. There was
the abstracted code on top and the hardware drivers on the bottom and very little in between.

There was not a clear distinction in style at various levels as in my code where
there were always someone else’s code layered under mine that I could not or
dared not change. Chuck’s code looked abstracted and high level right from
the bottom, the top used almost as many primitives as the bottom code.

Of course we had optimized the hardware to get an instruction set to
minimize the software required to build an optimizing native code
compiler for Forth. This new improved Forth virtual machine was
now no longer a virtual layer in software, it was a layer of hardware.
Chuck put most of his efforts into optimizing the hardware for speed
and simplicity after the specification to support the improved virtual
machine and simplified optimizing compiler that was about five years
old now. This also eliminated the need for an assembler layer,
our native code was Forth, Forth was the assembler. We couldn’t
have it much nicer than this.

I was working mostly with software for the actual chips while Chuck
focused on the hardware, and using and refining his CAD software to
aid him in this process. I observed that he applied the same
style to his work on his PC based CAD software to the software
intended for this own chips. I asked him about it and he said
that he just ported to Pentium by mapping the ideas without adding
any extra layers of abstraction. He said that his chips sort of
enforced good Forth style but that on Pentium it takes a little
more effort.

To jump forward another seven years, earlier
this month Chuck made a comment in an interview about
Forth in an Internet chat room. [Moore, 2002]
He was talking about the notions of
levels in the ANS Forth CATCH/THROW error handling method when he stated,
“What I do is to mix the low and high-level code into an integrated whole;
modify the low-level code as necessary for the application.
The notion of levels of code, as in communication protocols, is wrong.
There needn’t be so much code to make it necessary!”

It jumped out at me again. His approach is that there is a problem,
constrained by hardware, and an ideal solution expressed by
brevity, accuracy, reliability. In short quality. It’s
the ideal solution and nothing but the ideal solution.
Chuck’s code
has no layers that are fixed. He wrote all of it and it is as easy for
him to change any part of it as any other part of it. I knew
that. No wonder he doesn’t need all those levels. No wonder
he is so much more productive and writes so much better code. I had
written essays about this before, he doesn’t use all those layers
of abstractions. [Fox, 1998]

Later on in the chat session interview Chuck went on to say,
“Portability is not important.
Portability is not possible.
Real applications are closely coupled to hardware.
Change the platform and all the code changes.
If it didn’t, you wouldn’t have changed the platform.
To abstract the problem from the hardware requires massive software like Windows,
that’s a permanent tax on all applications to save some one-time programming.
Programmers should object to job-elimination concepts.
Of course, jobs are actually multiplied to deal with the hyper-complex abstraction.
And modern hardware has computers in the displays and disks.
They’ve already made many interfaces portable.
How many layers of portability are needed?”
[Moore, 2002]

Which brings me to the heart of the essay. Jack Woehr quotes
Chuck as saying, “Forth is more an approach than a specification for a
programming language.”
[Woehr, 1992]
Chuck said that the reason for Forth was to liberate the programmer,
to get them out from behind things that they couldn’t change, to let them
realize that idealized solution at the cutting edge of the capabilities
of any given the hardware, and to maximize their control over everything.
[Moore, 1970]

There is something that is a near mirror image of this and completely reversed.
The ANS Forth Programming Language
specification IS a formal specification for a programming language. Instead
of existing to avoid the inclusion of unwanted programming constraints on
a solution it formalizes further layers of mechanisms to embrace and mask
over these constraints, it adds to them.
It mandates adding a few further layers of abstraction in the name ‘portability.’
It loses any notion that the return stack is actually a return stack.
It looses any actual access to registers or even real memory.
It looses any notion of how anything works below more layers of abstraction.
It loses the real and useful behaviors of I/O devices behind layers
of abstraction.

Some authors of large ANS Forth systems
for popular environments have said that 99% of their work
and code was to deal with problems of the constraints
of the other abstracted layers in the systems into which they
integrate these ANS Forths. They tell us that these constraints dwarf the
standard Forth compilers themselves. This fact alone should account for Chuck’s
claim that they will write at least ten times as much code as he will
write to reach a solution. [Moore, 1999] I think Chuck is just being modest or hasn’t
paid close attention to just how much code these people have to write.
I think the evidence supports my claim that they are likely to write
a hundred times as much code as Chuck will write for a given
problem specification. Chuck has only claimed that ‘C’ programmers
write a hundred times more code than he will write. [Moore, 1999]

The ANS Forth standard is at least one, maybe two orders of magnitude
more complex than Mr. Moore’s approach to Forth. He says that code
should be so simple that most type of errors simply can’t happen.
In the late eighties and early nineties Chuck quit writing
code in Forth and experimented with sourceless programming. His first versions of
his VLSI CAD software, OKAD, were constructed without source using his tools
in his OK operating system. Later he return to Forth programming
and rewrote OKAD II under his new colorForth. [Moore, 2000]
In the chat session Chuck was asked,
“How did you come to the conclusion that Forth was too complex,
and that sourceless programming was your next move?”

His reply was,
“Maybe by reading the Forth Standard.” [Moore, 2002]

References:

[Fox, 1991] Fox, Jeffrey A.,
Forth-Linda Parallelizing Forth, FORML Conference Proceedings, 1991

[Fox, 1995] Fox, Jeffrey A.,
Distributed Shared Memory in Forth, Parallel Forth,
Internet, 1995

[Fox, 1993] Fox, Jeffrey A. and Montvelishsky, Michael,
F21 and F*F, Parallelizing Forth,
FORML Conference Proceedings, 1993

[Moore, 2002] Moore, Charles H.,
Internet Chat, May 5, 2002

[Fox, 1998] Fox, Jeffrey A.,
Low Fat Computing, Internet, 1998

[Woehr, 1992] Woehr, Jack J., Seeing Forth, page 83, available from Offete Enterprises,
San Mateo, CA, 1992

[Moore, 1970] Moore, Charles H. and Leach, Geoffrey C.,
FORTH – A Language for Interactive Computing
(pdf)
(html),
Amsterdam NY: Mohasco Industries, Inc. (internal pub.) 1970.

[Moore, 1999] Moore, Charles H.,
1x Forth, Charles Moore, Interview 4/13/99

[Moore, 1999] Moore, Charles H.,
Dispelling the User Illusion, SVFIG, 5/22/99

[Moore, 2000] Moore, Charles H.,
colorforth web site, Internet, 2000

Jeff Fox, 5/29/02

UltraTechnology.com homepage



http://www.ultratechnology.com/levels.htm