foldl laziness support. Reply

[Duncan Coutts]

On Mon, 2006-10-16 at 14:23 +0400, Serge D. Mechveliani wrote:
> Concerning the laziness support problem,
> 
> I thank people for explanations about  foldl and foldr.
> 
> >> I wonder how to avoid these numerous cost pitfalls.
> >> Maybe, the complier could do more optimization?
> 
> 
> Duncan Coutts <duncan.coutts at worc.ox.ac.uk>  writes
> 
> > There are important differences between foldl, foldl' and foldr. It is
> > quite important to choose the right one. I don't think this can be done
> > automatically.
> >
> > In my experience, the choice is almost always between foldl' and foldr.
> > 
> > [..]
> 
> I do not see  foldl'  in the standard library.
> Is it of the GHC lib extension?  has it strictness annotation?

It's in the standard Data.List module. It's not in the Prelude.

Duncan