Re: [stack] Properties of Concatenative langauges and Forth

Christopher Diggins <[email protected]> wrote:
> In a concatenative language, I believe evaluation order should be
> unimportant.
> For example:
> f g h <=> (f g) h <=> f (g h)

This is the associative property. You need to be careful calling it
"evaluation order", though; evaluation order matters with respect to
dataflow -- you can't fully evaluate an expression whose parameters
aren't all known at evaluation time.

> Does Forth have this property?

Yes, except where you're using macros or other compiling words.

> Another property that I expect from a concatenative language is that
> any subsequence of terms can be replaced with a subroutine whose
> definition consists of that subsequence, without changing the meaning
> of the program.

Yes; this is an important one for me. It's included in the new
proposed "Concatenative" page. It's actually a direct consequence of
the associative property.

> I believe this follows from the description of Joy
> that says that the syntax is a homomorphism to the semantics.

I'm not familiar with that claim, but it is indeed important that the
semantics and syntax have the same associative property. I don't know
whether that makes it a homomorphism.

I expressed this a while back by saying that "a concatenative language
maps the associative operation of syntactic concatenation onto the
semantics of an associative operation on functions." This isn't as
good of a definition as the others we're considering, but it does say
what you're examining here.

> Does Forth have this property?

Yes.

> What about Enchilada?

I believe so.

> FWIW: I like Steven Apter's informal definition a lot. Concatenative
> means Joy-like. I am really worrying so much about definitions because
> I am interested in trying to get at the heart of what makes Joy so
> darn interesting from a theoretical stand-point, so that I can talk to
> academics and say "see, Joy is not like your language!"

It's kind of odd to say that Postscript and Forth are Joy-like.

But really, as long as you're just going by examples, you don't have a
theory. That's okay; but it's not enough to make something interesting
from a theoretical standpoint.

> - Christopher

-Wm