Make lines stricter to fix a space leak

[Simon Marlow]

On 25/09/10 12:30, Ian Lynagh wrote:
> On Sat, Sep 25, 2010 at 03:45:15AM +0200, Daniel Fischer wrote:
>> On Saturday 25 September 2010 02:55:24, Ian Lynagh wrote:
>>> On Fri, Sep 24, 2010 at 09:21:19PM +0200, Daniel Fischer wrote:
>>>> Proposal: A stricter implementation of lines.
>>>>
>>>> Reason: The current implementation causes a space leak (cf.
>>>> http://homepages.inf.ed.ac.uk/wadler/papers/leak/leak.ps), at least in
>>>> GHC.
>>>>
>>>> The proposed implementation fixes the leak at the small cost of being
>>>> stricter if the first _|_ in the String is the first character of a
>>>> line.
>>>
>>> I think this changes the definition from one that currently has a space
>>> leak with GHC, to one which necessarily must have a space leak (as all
>>> of l must be held in memory while we look for a newline).
>>
>> No, with the proposed implementation, e.g. counting line lengths runs in
>> constant space:
>
> Ah, yes, you are right, sorry. I don't have a strong opinion, then.
>
> We ought to put the old definition into the H98 and H2010 packages,
> though. Hmm, but currently Prelude always comes from base.

Actually the haskell2010 package has its own Prelude, which could be 
different from the one in base if we wish.

Cheers,
	Simon