Re: [stack] Classifying languages by how they handle operands

On Jan 22, 2008, at 19:14 , William Tanksley, Jr wrote:

> Don Groves <[email protected]> wrote:
>> It occurred to me recently that one way to differentiate programming
>> languages is by how they handle operands.
>
> Sure thing -- sensible.
>
>> Lisp and its cousins use operands only once, placing them in a
>> structure preceded by an operator, (+ a b c) , effectively combining
>> their passing and evaluation.
>
> Let me add a word to your description:
> Lisp and its cousins place operands them in a *lexical* structure
> preceded by an operator, (+ a b c) , effectively combining their
> passing and evaluation.
>
> I also deleted "use operands only once", since I don't know what you
> mean by that. (What did you mean?)

Mea culpa, William, I should have said something like, "use operands in
only one form."

Many languages use operands in two distinct forms, one for evaluation,
x = a+b, and another for passing, DoSomethingWith(a,b). To me, the
combining of these into a single form is one of the beauties of Joy,
Lisp, etc.


>> The languages of interest to this group place operands in a structure
>> followed by a sequence of operators, (a b c) + +, which also combines
>> passing and evaluation.
>
> ...and here my modification is to stress that the structure is a  
> *semantic* one.
>
> The major difference is that the lexical structure is constrained to
> the medium of the language -- one-dimensional text parsed into a tree.
> A semantic structure can be more complex -- the operand flow for a
> stack language is a digraph rather than a tree.
>
> There are pros and cons to both.
>
>> While admittedly low level, is this concept worthy of further
>> discussion? Has it been discussed before, either here or elsewhere?
>
> I believe Manfred looked at it before... I can't recall which  
> paper, though.

Thanks, I'll look for it. And you make an excellent point about the  
lexical
vs. semantic structure.
--
Don


>> Don
>
> -Wm
>