[Haskell-cafe] On the purity of Haskell

[Conal Elliott]

I wrote that post to point out the fuzziness that fuels many discussion
threads like this one. See also
http://conal.net/blog/posts/notions-of-purity-in-haskell/ and the comments.

I almost never find value in discussion about whether language X is
"functional", "pure", or even "referentially transparent", mainly because
those terms are used so imprecisely. In the notions-of-purity post, I
suggest another framing, as whether or not a language and/or collection of
data types is/are "denotative", to use Peter Landin's recommended
replacement for "functional", "declarative", etc. I included some quotes
and a link in that post. so people can track down what "denotative" means.
In my understanding, Haskell-with-IO is not denotative, simply because we
do not have a (precise/mathematical) model for IO. And this lack is by
design, as explained in the "toxic avenger" remarks in a comment on that
post.

I often hear explanations of what IO means (world-passing etc), but I don't
hear any consistent with Haskell's actual IO, which includes
nondeterministic concurrency. Perhaps the difficulties could be addressed,
but I doubt it, and I haven't seen claims pursued far enough to find out.

  - Conal

On Thu, Dec 29, 2011 at 4:42 PM, Steve Horne <sh006d3592 at blueyonder.co.uk>wrote:

>  On 30/12/2011 00:16, Sebastien Zany wrote:
>
> Steve Horne wrote:
>
>> I haven't seen this view explicitly articulated anywhere before
>>
>
>  See Conal Elliott's blog post The C language is purely functional<http://conal.net/blog/posts/the-c-language-is-purely-functional>
> .
>
> Thanks - yes, that's basically the same point. More concise - so clearer,
> but not going into all the same issues - but still the same theme.
>
>
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