[Haskell-cafe] Data.ByteString.dropWhile

[Roman Leshchinskiy]

Thomas Conway wrote:
> Well, maybe I shoud be asking a higher level question then.
> 
> I have a function
> 
> tidy = reverse . dropWhile punk . reverse . dropWhile punk
>    where
>    punk = isPunctuation . chr . fromIntegral
> 
> which is leading to a significant amount of allocation, and you can see 
> why.
> 
> The way I'd like to write it is
> 
> tidy = dropWhile punk . dropWhileEnd punk
>    where ....
> 
> which has the obvious advantage of avoiding quite a bit of
> intermediate allocation.
> 
> Is there a another way?
> 
> I note that since I'm using a nice declarative language, the compiler
> CLEARLY should be transforming the first form into the second. :-)

The NDP library will implement this kind of fusion at some point 
(hopefully this year). We have a fairly clear idea of how to do it but 
not enough time.

Roman