[Haskell-cafe] Creating a instance for (Storable Text)

[David Feuer]

Chris Wong, the Storable class documents that sizeOf and alignmentOf
are not supposed to depend on the values they're passed. If the class
were being designed today, we'd likely have something more like

sizeOf :: proxy a -> Int

or possibly

sizeOf# :: Proxy# a -> Int#

But when Storable was designed, the proxy-passing "pattern" had not
yet been established.

On Thu, Nov 24, 2016 at 8:59 PM, Chris Wong <lambda.fairy at gmail.com> wrote:
> Since Text is represented as UTF-16 underneath, you can retrieve the
> length in terms of 16-bit code units.
>
> I don't think you'll be able to mmap them though, since the backing
> array may be moved by the garbage collector.
>
> See https://hackage.haskell.org/package/text-1.2.2.1/docs/Data-Text-Foreign.html
>
> On Fri, Nov 25, 2016 at 7:20 AM, Cody Goodman
> <codygman.consulting at gmail.com> wrote:
>> Any ideas on how I'd write this instance? I know for it to be storable it
>> needs a size, couldn't I just get the length of the text? Has anyone did
>> anything similar?
>>
>> I ran into a surprise when trying to use storable-record and derive-storable
>> and tried using them with a record that contained a Text field.
>>
>> My end goal is having a vector of records that could contain Text, UTCTime,
>> or other similarly complex types which I can write as an mmap to disk and
>> then read back to the original format.
>>
>> Thanks!
>>
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>
>
>
> --
> Chris Wong (https://lambda.xyz)
>
> "I had not the vaguest idea what this meant and when I could not
> remember the words, my tutor threw the book at my head, which did not
> stimulate my intellect in any way." -- Bertrand Russell
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