Re: [stack] disallowing recursive definitions

On Tue, Mar 4, 2008 at 12:42 AM, zallambo <[email protected]> wrote:
> --- In [email protected], Don Groves <dgroves@...> wrote:
> >
> >
> > On Mar 3, 2008, at 19:16 , John Nowak wrote:
> >
> > >
> > > On Mar 3, 2008, at 3:50 PM, William Tanksley, Jr wrote:
> > >
> > >>> With a concatenative tail-call you're passing the stack as an
> > >>> argument. In other words, you pass the entire state of the program!
> > >>
> > >> Yes, this is how concatenative languages are modeled. That's how
> > >> *every* step in their execution is modeled, not just tail-calls or
> > >> calls. If this were a problem, concatenative languages would be
> > >> universally problematic, not merely problematic in the presence of
> > >> tail-calls.
> > >
> > > Indeed, and I'd argue that this is exactly why many people find stack-
> > > based languages universally problematic. They're taking issue with all
> > > of this state passing, although they phrase it like "I can't keep the
> > > stack in my head". Of course this isn't a problem in practice,
> > > particularly when you have type inference involved and can get a quick
> > > summary of what a function cares about, but it does seem to be the
> > > source of many negative first impressions.
> >
> > Also, there has never been a requirement to "keep it all in one's head,"
> > that's what comments are for. Commenting with stack diagrams is very
> > useful!
> >
> > I know "real programmers" don't comment but in these languages, they
> > should.
> > --
> > don
>
> If code isn't readable without stack diagrams, comments seem like a
> poor fix. Rather, there should be a way to make the code itself more
> transparent. I think lambda expressions are a good replacement for
> stack diagrams. They make the stack explicit and are often easier to
> read. Compare:
>
> #x y u v -- (x*u - y*v) (x*v + y*u)
> dup4 [swap] dip * bury * swap - bury * bury * +
>
> [x y u v] [x u * y v * - x v * y u * +] lambda

<shamelessplug>

Cat supports this notation as: \x.\y.\u.\v.[x u * y v * - x v * y u * +]

</shamelessplug>