[Haskell-cafe] Re: HDBC, character encoding

Peter Gammie peteg42 at gmail.com
Fri Apr 4 02:06:21 EDT 2008

On 03/04/2008, at 9:10 PM, John Goerzen wrote:

> On 2008-04-01, Peter Gammie <peteg42 at gmail.com> wrote:
>> I added some stuff to HSQL (not HDBC) and HaskellDB so that UTF8 can
>> be used to talk to the database. It's not very pretty though, so I
>> haven't tried to get it merged.
> Do you have a diff somewhere?  I'd be interested in your approach, to
> see if the same thing would make sense in HDBC.

My approach is simple: when creating a connection to the database, ask  
for two functions (a codec pair) and stash them with the rest of the  
DB state. The types involved are [Word8] and String. I started out  
trying to use ByteString instead of [Word8] but it didn't bring much  
to the table in my case.

> I had generally been of the opinion that HDBC should just pass data
> through, however it is obtained, and let the programmer set the
> encoding as desired.  If this approach isn't working for people, I'd
> like to fix it, but want to make sure it's done right.

Assuming you're talking about the FFI's mandated behaviour, I'm not  
very comfortable with the encoding depending on the C locale, for two  
main reasons:

- the program I'm hacking runs on some web host's server that is an  
unknown quantity.
- GHC has a few quirks in how it implements the FFI, better to avoid  
the part that interprets characters.

If you want to be general, I guess you could abandon String (at the  
HDBC level) and use [Word8]/ByteString everywhere, then provide some  
convenience wrappers. Then you can uniformly handle binary and textual  
data. I am not familiar with your project though.


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