Re: [stack] disallowing recursive definitions

On Mar 3, 2008, at 19:06 , Christopher Diggins wrote:

> On Tue, Mar 4, 2008 at 12:42 AM, zallambo <[email protected]> wrote:
>> --- In [email protected], Don Groves <dgroves@...> wrote:
>>>
>>>
>>> On Mar 3, 2008, at 19:16 , John Nowak wrote:
>>>
>>>>
>>>> On Mar 3, 2008, at 3:50 PM, William Tanksley, Jr wrote:
>>>>
>>>>>> With a concatenative tail-call you're passing the stack as an
>>>>>> argument. In other words, you pass the entire state of the  
>>>>>> program!
>>>>>
>>>>> Yes, this is how concatenative languages are modeled. That's how
>>>>> *every* step in their execution is modeled, not just tail-calls or
>>>>> calls. If this were a problem, concatenative languages would be
>>>>> universally problematic, not merely problematic in the presence of
>>>>> tail-calls.
>>>>
>>>> Indeed, and I'd argue that this is exactly why many people find  
>>>> stack-
>>>> based languages universally problematic. They're taking issue  
>>>> with all
>>>> of this state passing, although they phrase it like "I can't  
>>>> keep the
>>>> stack in my head". Of course this isn't a problem in practice,
>>>> particularly when you have type inference involved and can get a  
>>>> quick
>>>> summary of what a function cares about, but it does seem to be the
>>>> source of many negative first impressions.
>>>
>>> Also, there has never been a requirement to "keep it all in one's  
>>> head,"
>>> that's what comments are for. Commenting with stack diagrams is very
>>> useful!
>>>
>>> I know "real programmers" don't comment but in these languages, they
>>> should.
>>> --
>>> don
>>
>> If code isn't readable without stack diagrams, comments seem like a
>> poor fix. Rather, there should be a way to make the code itself more
>> transparent. I think lambda expressions are a good replacement for
>> stack diagrams. They make the stack explicit and are often easier to
>> read. Compare:
>>
>> #x y u v -- (x*u - y*v) (x*v + y*u)
>> dup4 [swap] dip * bury * swap - bury * bury * +
>>
>> [x y u v] [x u * y v * - x v * y u * +] lambda
>
> <shamelessplug>
>
> Cat supports this notation as: \x.\y.\u.\v.[x u * y v * - x v * y u  
> * +]
>
> </shamelessplug>


Naming stack locations is a nice way to reduce the cognitive load
and it looks like it works particularly well for mathematical  
algorithms.
How well does it work for non-mathematical things?
--
don



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