[Haskell-cafe] On the purity of Haskell

[Conal Elliott]

On Fri, Dec 30, 2011 at 9:30 AM, Colin Adams <colinpauladams at gmail.com>wrote:

>
>
> On 30 December 2011 17:27, Conal Elliott <conal at conal.net> wrote:
>
>>  On Fri, Dec 30, 2011 at 9:20 AM, Colin Adams <colinpauladams at gmail.com>wrote:
>>
>>>
>>> proof: f is a function, and it is taking the same argument each time.
>>> Therefore the result is the same each time.
>>>
>>
>> Careful of circular reasoning here. Is f actually a "function" in the
>> mathematical sense? It's that math sense that you need to reach your
>> conclusion.
>>
>> Yes. Because Haskell is a functional programming language.
>

And how do you know that claim to be true?

And do you mean a *purely* functional language? Otherwise f might be in the
impure part. If you do mean *purely* functional, aren't you arguing for
purity by assuming purity?

Moreover, do you have a precise definition for "functional"? I've witnessed
a lot of these arguments and have seen a diversity of interpretations.
Which is why I recommend shifting away from such fuzzy terms and following
Peter Landin's recommended more precise & substantive replacement, namely
"denotative". (See
http://conal.net/blog/posts/is-haskell-a-purely-functional-language/#comment-35882for
a quote and reference.)

  - Conal
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