Re: Avoiding side effects

[Anders Wirzenius <anders@no.email.thanks.invalid>]

"(see below)" <yaldnif.w@blueyonder.co.uk> writes:

> On 08/10/2008 06:16, in article u1vyrbra1.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 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 ;-)
> > 
> > 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 avoid side effects. 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 having side effects. 

Is the dogm you refer to something like "functions without side
effects". 

I am not a professional programmer any more and I just
wanted to learn something about side effects. What is silly in
that?


-- 
Anders