Re: [stack] Re: the concatenative wikipedia article

On Dec 31, 2008, at 4:24 PM, John Nowak wrote:

> On Dec 31, 2008, at 6:54 PM, Don Groves wrote:
>
>> I was leaning toward defining a concatenative (if that's the right
>> word) program as "a list of operators applied to a (possibly  
>> initially
>> empty) list of operands."
>
> I don't think this is a satisfactory definition for a few reason:
>
> 1. What exactly is a "list of operators"? Do you mean a sequence of
> functions reified as a list of objects? I don't think that's  
> necessary.

As I now belatedly recall, no doubt prompted by your words, I was
using "sequence of operators" and "sequence of operands" rather
than lists.


> 2. For me, the main advantage of a concatenative language is that you
> get rid of application. Manfred von Thun pointed this out in his "Joy
> compared with other functional languages" paper and I think it is
> critical to the definition of concatenative languages.

I'll review that paper. Perhaps my use of of the word "application" to
indicate the catenation of two sequences, e.g., [a b] [+] is confusing.


> 3. There's no reason that the data structure the functions operate on
> be a list or a stack. I recently proposed a language using vectors in
> the style of More's array theory. Earlier today, Chris proposed a
> language based on a deque. I believe XY works on a stack/queue tuple.
> Other possibilities are easy to dream up.

The reason I picked "sequence" is that it seems to be the most basic
ordered structure.


>> the order of application is not specified.
>
> This would depend on the language in question. Various evaluation
> strategies can be employed. In a language with side effects, the order
> of reduction is going to be important. One could even imagine a
> language with a term rewriting semantics that allows definitions of
> the form 'dup drop  -> id'. If your rewrite rules aren't confluent,
> the way in which you reduce will matter.

Many thanks for taking the time to comment, John. I'll tuck this away
with my notes for when the urge strikes again...
--
don

> - John