Proposal: Make intersperse lazier

[Daniel Fischer]

On Thursday 16 September 2010 17:08:08, Duncan Coutts wrote:
> On 16 September 2010 15:39, Daniel Fischer <daniel.is.fischer at web.de> 
wrote:
> > The current implementation of Data.List.intersperse causes a space
> > leak under certain not uncommon circumstances.
> > Trac ticket: http://hackage.haskell.org/trac/ghc/ticket/4282
> > The proposed implementation,
> >
> > changes the semantics from
> >
> > intersperse (x : _|_) = _|_
> >
> > to
> >
> > intersperse (x : _|_) = x : _|_
>
> You mean:
>
> intersperse sep (x : _|_) = x : _|_

Oops, of course.

>
> We would also need to change intercalate to match:
>
> intercalate sep (x : _|_) = x ++ _|_
>
> Note that the current definition of intercalate in the base package
> will not need to change because it is defined in terms of intersperse,
> but its strictness specification does change.
>
> Assuming the proposal is updated with the corresponding change to
> intercalate,

You mean, also mention the consequences for intercalate explicitly?
Or something more/else?

> then I support the proposal. It is in the spirit of the
> Haskell98 List module for list functions to be as lazy as possible
> (except there are good reasons to be stricter, e.g. as in splitAt).
> Incidentally, the lazier version is also slightly more efficient.
>
> Duncan