Re: [stack] are concatenative languages applicative?

On 25/4/08 11:58 AM, "Don Groves" <[email protected]> wrote:

> On Apr 24, 2008, at 3:10 PM, John Nowak wrote:
> 
>> > First off, let me say that I'm not particularly interested in if Joy's
>> > 'i' is an 'eval'. This does, as Chris pointed out, seem to get us
>> > bogged down in implementation details.
> 
Emphatically, it is not an implementation detail. Any programming
language ultimately runs in machine language, which is sequential
(with jumps, though). At intermediate levels it can be implemented
in functional or in procedural languages. Any functional language
can be implemented in a functional or a procedural language, or
by rewriting ­ even concurrent rewriting. The details of the rewriting
will depend on the syntax of the functional language. For a
concatenative language, here is a (crazy, but correct) algorithm
for rewriting an expression in the language, using several clerical
workers concurrently:
> 
REPEAT:
    The workers at random select an operator in the expression.
    If it is immediately preceded by the appropriate number of
    operands, replace the operands and the operator by a value.
    (For example, (... 2  3 +  ...) is replaced by (... 5 ...).)
UNTIL there are no more operators in the expression
> 
This is a way of implementing any concatenative language, even
if crazy. The usual stack implementation of concatenative languages
is just an efficient way of finding operators that are immediately
preceded by their operands.

Whether Joy¹s i combinator is an eval is a semantic question that
is independent of the implementation, whether by stack or by
rewriting.
> 
 - Manfre


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