[Haskell-cafe] On the purity of Haskell

[Bardur Arantsson]

On 12/29/2011 07:07 PM, Steve Horne wrote:
> On 29/12/2011 10:05, Jerzy Karczmarczuk wrote:
>> Sorry, a long and pseudo-philosophical treatise. Trash it before reading.
>>
>> Heinrich Apfelmus:
>>> You could say that side effects have been moved from functions to
>>> some other type (namely IO) in Haskell.
>> I have no reason to be categorical, but I believe that calling the
>> interaction of a Haskell programme with the World - a "side effect" is
>> sinful, and it is a source of semantical trouble.
>>
>> People do it, SPJ (cited by S. Horne) did it as well, and this is too
>> bad.
>> People, when you eat a sandwich: are you doing "side effects"?? If you
>> break a tooth on it, this IS a side effect, but neither the eating nor
>> digesting it, seems to be one.
>>
> By definition, an intentional effect is a side-effect. To me, it's by
> deceptive redefinition - and a lot of arguments rely on mixing
> definitions - but nonetheless the jargon meaning is correct within
> programming and has been for decades. It's not going to go away.
>

This doesn't sound right to me. To me, a "side effect" is something 
which happens as a (intended or unintended) consequence of something 
else. An effect which you want to happen (e.g. by calling a procedure, 
or letting the GHC runtime interpreting an IO Int) is just "an effect".