Proposal: Don't require users to use undefined

[Bas van Dijk]

On Tue, Oct 26, 2010 at 8:06 PM, Roman Leshchinskiy <rl at cse.unsw.edu.au> wrote:
> On 26/10/2010, at 17:15, Bas van Dijk wrote:
>
>> malloc :: Storable a => IO (Ptr a)
>> malloc  = doMalloc undefined
>>  where
>>    doMalloc       :: Storable b => b -> IO (Ptr b)
>>    doMalloc dummy  = mallocBytes (sizeOf dummy)
>>
>> I find the use of 'undefined' ugly;
>
> How about:
>
> malloc :: Storable a => IO (Ptr a)
> malloc  = doMalloc Nothing
>  where
>   doMalloc       :: Storable b => Maybe b -> IO (Ptr b)
>   doMalloc dummy  = mallocBytes (sizeOf dummy)

I don't think this will work because 'Maybe a' doesn't have a Storable instance.

> or perhaps
>
> data Dummy a = Dummy
>
> malloc :: Storable a => IO (Ptr a)
> malloc  = doMalloc Dummy
>  where
>   doMalloc       :: Storable b => Dummy b -> IO (Ptr b)
>   doMalloc dummy  = mallocBytes (sizeOf dummy)

Again I think this won't work because you need to add a Storable instance like:

instance Storable a => Storable (Dummy a) where
  sizeOf _ = sizeOf (undefined :: a)
  peek = ...
  poke = ...
  ...

Regards,

Bas