Re: [stack] S-K Construction of Dip?

On 3/4/07 9:12 AM, "William Tanksley, Jr" <[email protected]> wrote:
> 
> Manfred Von Thun <[email protected] <mailto:m.vonthun%40latrobe.edu.au>
> > wrote:
> 
> Thank you for the prompt and clear answers. To cut to the chase: I
> agree that the language "L" is both flat and concatenative, and that L
> is not enormously different from Joy.

Indeed, not enormously. But see below.

[..]

> However...
> 
> My first reaction was that although I confess that I have researched
> flatness for its own sake, I suspect that there are higher principles
> in language design than perfect flatness, and I believe that L's
> design compromises some of them. I don't think that's a bad thing --
> but I did believe that unless I point out the problems, the obvious
>> > I don¹t know what you mean by an unbalanced foyer. If you mean something
>> > like unbalanced parentheses, then you should get the warning in this L
>> > (whereas it
>> > would be an errorr in Joy):
>> > ³Incomplete program? more than one foyer remaining. See top foyer?²
> 
> Again, I was talking about Joy. Joy is not flat; it doesn't depend on
> your perspective. L _is_ flat; again, it doesn't depend on your
> perspective.

See your own comment above. You agree that L is concatenative (and flat),
and that Joy is concatenative (but not flat). I thought it was clear that
they
accept the same programs ­ more or less, perhaps. If so, then flatness is
in the eye of the beholder.

It seems we need a definition of identity between two programming languages.
(And keep in mind that any single language might have several very different
implementations.) Here is one attempt at a definition:

L1 is a sublanguage of L2 if and only if
For all programs P, if P is a correct program in L1, then P is a correct
program in L2,
and for all inputs I, program P with input I produces the same output in L1
and in L2.

L1 is identical with L2 if and only if they are sublanguages of each other.

I claim that Joy and L are identical in this sense ­ apart from the trivial
sense
that an incomplete Joy program (as Joy is currently implemented) produces
an error message (³end of input file, incomplete program²), whereas L
would not consider it to be incomplete. But surely this is a trivial
difference,
and is easily removed,

[..]
> 
>>> > > One thing I'm not clear on, though. Are these foyers available at
>>> > > runtime?
> 
>> > Yes, in the L-definition of runtime. This is not your definition, I know.
> 
> I think it is my definition as well -- what am I missing
> 
In most languages there is scantime, parsetime and runtime. In L there
are only scantime and runtime.
> 
> 
> 
>> > But
>> > L has a right to make its own definition. In L one would define your notion
>> > of runtime as: executing the content of the topmost foyer using the
>> > ONLY remaining foyer below as its stack. But the executions of topmost
>> > foyers would be exactly the same if there are further foyers below.
> 
> Nope, that's runtime. We're good.
> 
>>> > > In practical terms: if I split a Joy definition into two
>>> > > parts (cutting in the middle of a quotation), giving each part of the
>>> > > definition its own name, and then I define a function which contains
>>> > > the two parts one after the other, is the resulting definition
>>> > > equivalent to the original? For example:
> 
>> > Since when does being able to give names to the parts have anything to
>> > do with cuttability or flatness?
> 
> It doesn't -- names help clarify things. I assume syntax to assign
> names for the sake of clarity. If asked the same question about my 01
> language, I would assume the same thing.
> 
>>> > >DEFINE
>>> > >  Csucc   ==  [dup [i] dip] dip i.
>>> > >DEFINE
>>> > >  CsuccA == [dup [i];
>>> > >  CsuccB ==  dip] dip i;
>>> > >  CsuccC == CsuccA CsuccB.
> 
>>> > > Is CsuccC exactly the same as Csucc? Would it still be the same if
>>> > > CsuccC were defined in a DEFINE block apart from CsuccA or CsuccB?
> 
>> > I have not said anything about definitions in L, and your example does
>> > show that if L is to be of interest at all, then L needs to use a different
>> > style of definitions. Thank you.
> 
> Interesting. How would they differ?

Note the ³.² at the end of these definitions. If ³.² is to be allowed inside
a definition,
then a different notation might be needed, something like:

DEFINE a == ...; b == ...; c == ... END_DEF
> 
[..]
> 
>> > Thanks for the discussion, Billy. I hope I have cleared up a few things.
> 
> You certainly did! I hope I make more sense now that we're on the same page.
> 
>> >   - Manfred
> 
> -Billy
>  
 - Manfred    


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