Maybe you want to use Data.Serialize? Encode to and from a bytestring. On Nov 24, 2016 1:24 PM, "Michael Snoyman" wrote:

It can't be done. Instances of Storable need to have a fixed serialized size, and Text values don't.

On Thu, Nov 24, 2016, 8:21 PM Cody Goodman 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! _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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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 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 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)

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