From: Paul Moore [mailto:p.f.moore@gmail.com]
If you don't need the entire list at once, then push your processing into the iteratee.
Hmm, that's what I was trying to avoid. The article I mentioned made a strong point that laziness allows you to factor out processing from IO - so you can write (for example)
main = do s <- getContents let r = map processIt (lines s) putStr (unlines r)
and laziness means that IO is performed "on demand", so that the above code never has to read the whole input into memory. I was hoping to do something similar for database access, with runSql taking the place of getContents. Having to incorporate "processIt" into the database access code breaks this idiom.
There's a big difference between getContents and Takusen: getContents has a non-trivial implementation (using unsafeInterleaveIO) that allows it to return data lazily. Takusen has no such implementation. I'm not sure if it would be possible. I don't really understand how getContents works; is there any advice or guidelines as to how to use (or abuse) unsafeInterleaveIO? Some googling has found: http://therning.org/magnus/archives/249 http://www.haskell.org/pipermail/haskell-cafe/2007-January/021373.html http://www.haskell.org/pipermail/haskell-cafe/2007-January/021407.html http://haskell.org/haskellwiki/IO_inside#unsafePerformIO_and_unsafeInter leaveIO
That's what my earlier code looked like, and I found it harder to understand than the getContents/process/put approach. I'm trying to explore ways of factoring data manipulation code out of database access functions, but maybe that's not the right way of doing it.
I don't think it's possible to pursue this style of programming with Takusen. If you do, you'll have to process the entire result-set into a data structure and then process it, which has obvious memory implications. Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************