[Haskell-cafe] Handling custom types in Takusen

[Bayley, Alistair]

> From: Salvatore Insalaco [mailto:kirby81 at gmail.com] 
> 
> 2007/7/27, Bayley, Alistair <Alistair_Bayley at invescoperpetual.co.uk>:
> > > Also, in Sqlite 3.4, they introduced new functions for incremental
> > > reading / writing of Blobs. I could use them in the future.
> >
> > Seems reasonable. I recall Oleg saying something privately 
> a while ago
> > about an API for large objects. He may have some ideas for this.
> 
> A good idea could be to do the marshalling / unmarshalling of Blob as
> CStringLen. It can then be used to construct PackedStrings and
> ByteStrings in O(1), or doing some custom computations with it. A
> CStringLen, even if contains Ptr CChar, can easily be converted to any
> pointer type.
> 
> Another idea could be using custom bind function for blobs, but the
> first solution is surely easier.

It was my intention to do it the other way around: marshall blob to Ptr
(), and then you can cast this to a Ptr CChar. Obviously you'd need to
retain the size information, so a blob basically becomes a (Ptr (), Int)
pair, just like a CStringLen...

At least this way you've got a type which says explicitly "this thing is
a blob", and then if you know better, i.e. it's really a CString, you
can cast it.

Actually, it wouldn't cost much to have both marshalling functions in
the low-level API, even if they both call the same Sqlite blob retrieval
function.

Alistair
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