Re: [stack] disallowing recursive definitions

On 8/3/08 3:03 AM, "John Cowan" <[email protected]> wrote:
> 
> ....
> Assembler: the ultimate concatenative language....

Indeed, except for those jumps, as of course you know. But the
mention of assembler triggers an old memory about something
I have wanted to write about for some time. It concerns not
so much the high or low level of a concatenative language,
but what its shortest programs are whose concatenation
computes the composition of what those shortest programs
are. In just about all concatenative languages the shortest
programs are atoms like swap, +, map, 123, ³hello², [a b],
the first three operators and the lest three push-ops. It is
from atoms such as these that programs are constructed by
concatenation. But could there not be small programs, not
formed by concatenating with others to form their composition,
which nevertheless have parts: MOLECULES

An assembly program consists of a sequence of lines, each
holding one instruction, to be executed in sequence unless
intercepted by a jump instruction. Each instruction produces
a change somewhere, and the concatenation of the lines
produces the composition of the changes. But instructions
have part, too. They consist of an operator such as mul, fetch,
store, ..., each followed by several inscrutables having to
do with where things come from and where they should go.
So an instruction is a sort of molecule composed of several
atoms. Now think of concatenative languages in which programs
are concatenated from molecules, each consisting of an
operator (like swap, + etc) together with additional parts
that complete what is meant. Note that the additional parts
are not further parameters that should be taken from the stack.
What useful additional parts may there be?

I would take a hint from unix, which has a rich collection of
what are called filters, programs that take one input fil and
produce one output file. The names of such programs, foo, bar,
baz and zot, can be concatenated to form what is called a pipe:
(here i dare not think what my mailer will do with the vertical bar)

foo | bar | baz | zot

and this concatenation will take one input file and produce one
output file such that ... You guessed it. But each of these programs
may have a useful default behaviour and also allow switches to
modify the default. The switches are typically single letters
precededd by a minus sign. So the pipe might actually look like
this:

foo ­a ­g | bar ­x | baz -e ­q ­w ­e ­r | zot ­m ­d

So in the terminology I am tempted to adopt, here we have
the concatenation of four molecules or instructions,
where the first instruction consists of  three atoms, namely
a program and two switches.

Apart from the pipe of output-input files, it may be necessary
to use other files, and there are lots of ways of doing that.

The upshot: have we in the concatenative world missed out
on something useful by not allowing parts to the smallest
programs. There is a lot one could and should discuss here,
but not me, not tonight.

  - Manfred



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