Re: Avoiding side effects

["(see below)" <yaldnif.w@blueyonder.co.uk>]

On 13/10/2008 14:21, in article
c3d10577-421a-4fb0-b27f-1395df583dd9@w1g2000prk.googlegroups.com, "Marco"
<prenom_nomus@yahoo.com> wrote:

> On Oct 13, 5:27 am, Anders Wirzenius <and...@no.email.thanks.invalid>
> wrote:
>> "(see below)" <yaldni...@blueyonder.co.uk> writes:
>>> On 08/10/2008 06:16, in article u1vyrbra1....@no.email.thanks.invalid,
>>> "Anders Wirzenius" <and...@no.email.thanks.invalid> wrote:
>> 
>>>> "(see below)" <yaldni...@blueyonder.co.uk> writes:
>> 
>>>>> On 07/10/2008 15:47, in article uprmc4g3i....@no.email.thanks.invalid,
>>>>> "Anders Wirzenius" <and...@no.email.thanks.invalid> wrote:
>> 
>>>>>> "(see below)" <yaldni...@blueyonder.co.uk> writes:
>> 
>>>>>>> On 07/10/2008 12:08, in article wvbrfxn8hdc7....@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 havesideeffects 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 withoutsideeffects. 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 ;-)
>> 
>>>> function Row_Number (Row_Number_In_Other_Array : in
>>>>                      Row_Number_Type)  return Row_Number_Type is
>>>>    --  Return a row number one higher than the row number of the row
>>>>    --  identical to the row in the other array.
>> 
>>> I think this beautifully illustrates the silliness that slavish adherence to
>>> dogma inevitably produces, in programming as in finance and politics.
>> 
>> The thread I started was about how to avoidsideeffects. From
>> the answers I have been reading that for a case where you compare
>> the content of two files, it is rather hard to do it with
>> functions without havingsideeffects.
>> 
>> Is the dogm you refer to something like "functions withoutside
>> effects".
>> 
>> I am not a professional programmer any more and I just
>> wanted to learn something aboutsideeffects. What is silly in
>> that?
> 
>   nothing, but I agree don't get carried away with the concept,
> Functional Programming is kind of an extreme backlash to the Object
> Oriented push of the late 80's and 90's, in the end, both are useful

FP started with LISP, ca. 1960, and turned into a major academic industry in
the early 1980s. Only AI rivals it as a wholesale waste of CS effort.

> but is important to keep as many functions "pure" as possible because
> these tend to be easier to verify and are more reusable in other
> contexts.
> 
>  http://en.wikipedia.org/wiki/Pure_function
> 
>  At work, we are trending away from the pure OO stuff to a mixed
> approach.

-- 
Bill Findlay
<surname><forename> chez blueyonder.co.uk