Call to arms: lambda-case is stuck and needs your help

[Mikhail Vorozhtsov]

On 07/09/2012 09:49 PM, Simon Marlow wrote:
> On 09/07/2012 15:04, Mikhail Vorozhtsov wrote:
>> Hi Simon.
>>
>> On 07/09/2012 08:23 PM, Simon Marlow wrote:
>>> On 07/07/2012 16:07, Strake wrote:
>>>> On 07/07/2012, Jonas Almström Duregård <jonas.duregard at chalmers.se>
>>>> wrote:
>>>>> Couldn't we use \\ for multi-case lambdas with layout?
>>>>>
>>>>> If not, these are my preferences in order (all are single argument
>>>>> versions):
>>>>> 1: Omission: "case of". There seems to be some support for this but it
>>>>> was not included in the summary.
>>>>> 2: Omission with clarification: "\case of"
>>>>> 3: "\of"  - but I think this is a little weird. It's nice to have
>>>>> short keywords but not at the expense of intuition. The goal here is
>>>>> to drop the variable name not the case keyword, right?
>>>>>
>>>>> Regards,
>>>>> Jonas
>>>>
>>>> Well, since this is now suddenly a ranked-choice election, I shall
>>>> re-cast my vote:
>>>
>>> I think some misunderstanding has crept in - we're not planning to count
>>> votes or anything here.  If you have new suggestions or know of reasons
>>> for/against existing proposals then please post, otherwise there's no
>>> need to post just to express your personal preference.
>> Could you express your opinion on the case "comma sugar", i.e.
>>
>> case x, y of
>>    P1, P2 -> ...
>>    P3, P4 -> ...
>>
>> as sugar for
>>
>> case (# x, y #) of
>>    (# P1, P2 #) -> ...
>>    (# P3, P4 #) -> ...
>
> I like this.
Good!

>
>> and respectively
>>
>> \case
>>    P1, P2 -> ...
>>    P3, P4 -> ...
>>
>> as sugar for
>>
>> \x y -> case x, y of
>>    P1, P2 -> ...
>>    P3, P4 -> ...
>
> That looks a bit strange to me, because I would expect
>
>   \case
>      P1, P2 -> ...
>      P3, P4 -> ...
>
> to be a function of type (# a, b #) -> ...
Hm, maybe I put it slightly wrong. Desugaring is really only a means of 
implementation here. Would you still expect tuples for \case if you 
didn't see the way `case x, y of ...` was implemented (or thought that 
it is a primitive construct)?