[Haskell-cafe] Reply-To: Header in Mailinglists (was: About "Fun with type functions" example)

[Jeremy Shaw]

Reply-to munging  has come up many times on this list (and others).
See this page for information on why many people do not like Reply-to
munging:

http://marc.merlins.org/netrants/listreplyto.html

- jeremy

On Thu, Nov 18, 2010 at 9:55 PM, Bastian Erdnüß <earthnut at web.de> wrote:
> Hi there,
>
> I just put an answer two this in beginners at haskell.org.  It was not on purpose to move the topic.  It's just that questions I feel I can answer are usually beginner level questions and so I'm not often writing in the cafe itself.
>
> It would make my life a little bit more easy if the mailing lists on haskell.org would add a Reply-To: header automatically to each message containing the address of the mailing list, the message was sent to.  Usually that's the place where others would want to sent the answers to, I would suppose.
>
> Is there a reason that that's not the case?  Am I missing something?  Or am I supposed to install a more cleaver mail client which can do that for me?  Is there one?  Probably written in Haskell ;-)
>
> Cheers,
> Bastian
>
> On Nov 19, 2010, at 1:07, Daniel Peebles wrote:
>
>> The best you can do with fromInt is something like Int -> (forall n. (Nat n)
>> => n -> r) -> r, since the type isn't known at compile time.
>>
>> On Thu, Nov 18, 2010 at 2:52 PM, Arnaud Bailly <arnaud.oqube at gmail.com>wrote:
>>
>>> Thanks a lot, that works perfectly fine!
>>> Did not know this one...
>>> BTW, I would be interested in the fromInt too.
>>>
>>> Arnaud
>>>
>>> On Thu, Nov 18, 2010 at 8:22 PM, Erik Hesselink <hesselink at gmail.com>
>>> wrote:
>>>> On Thu, Nov 18, 2010 at 20:17, Arnaud Bailly <arnaud.oqube at gmail.com>
>>> wrote:
>>>>> Hello,
>>>>> I am trying to understand and use the Nat n type defined in the
>>>>> aforementioned article. Unfortunately, the given code does not compile
>>>>> properly:
>>>>
>>>> [snip]
>>>>
>>>>> instance (Nat n) => Nat (Succ n) where
>>>>> toInt   _ = 1 + toInt (undefined :: n)
>>>>
>>>> [snip]
>>>>
>>>>> And here is the error:
>>>>>
>>>>> Naturals.hs:16:18:
>>>>>   Ambiguous type variable `n' in the constraint:
>>>>>     `Nat n' arising from a use of `toInt' at Naturals.hs:16:18-39
>>>>>   Probable fix: add a type signature that fixes these type variable(s)
>>>>
>>>> You need to turn on the ScopedTypeVariables extension (using {-#
>>>> LANGUAGE ScopedTypeVariables #-} at the top of your file, or
>>>> -XScopedTypeVariables at the command line). Otherwise, the 'n' in the
>>>> class declaration and in the function definition are different, and
>>>> you want them to be the same 'n'.
>>>>
>>>> Erik
>>>>
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