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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Avoiding side effects
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References: <uljxa9o85.fsf@no.email.thanks.invalid> <wvbrod23gnol.fsf@sun.com>
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Date: Wed, 8 Oct 2008 09:35:43 +0200
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Date: 2008-10-08T09:35:38+02:00
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On Wed, 08 Oct 2008 05:16:22 GMT, Anders Wirzenius wrote:

> "(see below)" <yaldnif.w@blueyonder.co.uk> writes:
> 
>> On 07/10/2008 15:47, in article uprmc4g3i.fsf@no.email.thanks.invalid,
>> "Anders Wirzenius" <anders@no.email.thanks.invalid> wrote:
>> 
>>> "(see below)" <yaldnif.w@blueyonder.co.uk> writes:
>>> 
>>>> On 07/10/2008 12:08, in article wvbrfxn8hdc7.fsf@sun.com, "Ole-Hjalmar
>>>> Kristensen" <ole-hjalmar.kristensen@substitute_employer_here.com> wrote:
>>>> 
>>>>> Yes, I think any program which use a read/write interface to a file
>>>>> will have side effects in that sense. The only way I can think of for
>>>>> avoiding this would be to mmap the whole file, then it will appear as
>>>>> an array of bytes.
>>>> 
>>>> Why would stepping through an array not be thought a "side" effect?
>>> 
>>> A function that returns the row of that array and only that
>>> would perhaps be a function without side effects. The information
>>> in that row can be fetched when needed.
>> 
>> A function that always returns the same row of an array would be of little
>> use, I should think.
> 
> I have a feeling that the function can be programmed so that it returns
> different row (numbers, or pointers in that array) depending on
> the content of the rows in that array ;-)

... which (content) cannot itself be a function, when mutable. There is no
way out of "functional singularity." (:-))

Even a pure function is not a function in the promoted sense. It is a
subroutine with one dedicated out parameter, called "result," such that all
effect of execution is limited to that parameter.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de