Re: [stack] function/object ambiguity + quotation alternative

--- In [email protected], William Tanksley
<wtanksleyjr@...> wrote:
>
> Stevan Apter wrote:
> > From: "John Nowak" <john@...>
> > > What XY does seems even worse though! Here's why:
> > >    1. [dup] i == [dup] first i  (given, as per your example)
> > >    2. [dup] == [dup] first      (removing shared 'i' suffix)
> >>    3. id == first               (removing share '[dup]' prefix)
> 
> > no.  dup = [dup] first.
> 
> You're right, but he's also right -- you should always be able to remove
> identical suffixes from both sides of the equation, and in this case you
> can't do that.
> 
> -Wm
>


(2) does not follow from (1) and (3) does not follow from (2). In
general, you *cannot* remove common prefixes and suffixes. For instance,

If you could remove prefixes, then
   [dup] dup == [dup] [dup]
=> dup == [dup].

If you could remove suffixes, then
   2 [id] i == 1 [inc] i
=> 2 [id] == 1 [inc].

There's nothing special about concatenative languages in this regard;
as long as there are functions that aren't reversible (i.e. are not
one-to-one and onto), f(a) = f(b) does not imply a = b. And f(a) =
g(a) does not imply f = g.


I think John has a point though. We need a way to distinguish between
the function 'dup' and the object 'dup'. I suggest putting a single
quote in front of objects, like symbols in Scheme. So

[dup] i == dup
[dup] first == 'dup

However, we *don't* need to distinguish the number 42 from the
function 42. Pushing the number 42 on the stack is exactly the same as
applying the function 42 to the stack. So

[42] i == [42] first
42 == '42


Does anyone have another syntax for writing 'dup? I cannot recall
seeing any.

Justin