[Haskell-cafe] Fwd: rolling span and groupBy for lists

[Harendra Kumar]

I guessed so and subscribed, CCing again to the libraries list, hoping it
will work this time. I think instead of saying "You are not allowed to post
to this mailing list" the message should say "You need to subscribe to post
to this list" and it can provide info about how to subscribe as well. Is it
too problematic (spam?) if these lists are open to all?

-harendra

On 5 February 2018 at 12:05, Markus Läll <markus.l2ll at gmail.com> wrote:

> Hi Harendra -- I think you just need to register to libraries at haskell.org
> to post there.
>
> On Mon, Feb 5, 2018 at 6:02 AM, Harendra Kumar <harendra.kumar at gmail.com>
> wrote:
>
>> Hi,
>>
>>
>> I am looking for the decision making authority or a place where questions
>> about haskell libraries like in the email below can be asked or answered.
>> ghc-devs told me that their list is not the right place for this and
>> redirected me to haskell-cafe or libraries at haskell.org. I tried sending
>> an email to libraries at haskell.org but that seems to be a closed list, my
>> email got rejected, so that also does not seem like the right place. Is
>> haskell cafe the right place? I was under the impression that
>> haskell-cafe is for general discussions and not an owner of any of the
>> libraries or any other haskell code. Are there any other mailing lists that
>> I am missing? I can raise a ticket at ghc trac but I guess that cannot be
>> the primary way to ask simple questions.
>>
>> -harendra
>>
>> ---------- Forwarded message ----------
>> From: <libraries-owner at haskell.org>
>> Date: 5 February 2018 at 09:34
>> Subject: Re: rolling span and groupBy for lists
>> To: harendra.kumar at gmail.com
>>
>>
>> You are not allowed to post to this mailing list, and your message has
>> been automatically rejected.  If you think that your messages are
>> being rejected in error, contact the mailing list owner at
>> libraries-owner at haskell.org.
>>
>>
>>
>>
>> ---------- Forwarded message ----------
>> From: Harendra Kumar <harendra.kumar at gmail.com>
>> To: David Feuer <david at well-typed.com>, libraries <libraries at haskell.org>
>> Cc: ghc-devs at haskell.org
>> Bcc:
>> Date: Mon, 5 Feb 2018 10:07:55 +0530
>> Subject: Re: rolling span and groupBy for lists
>> I was mainly asking if it makes sense to include these functions in
>> base/Data.List. Since the base package is maintained and ships along with
>> ghc, and the issues are also raised at ghc trac I thought this is the right
>> list. I am copying to libraries at haskell.org as well.
>>
>> -harendra
>>
>> On 5 February 2018 at 09:53, David Feuer <david at well-typed.com> wrote:
>>
>>> This is the wrong list. You probably meant to email haskell-cafe or
>>> perhaps libraries at haskell.org.
>>>
>>>
>>>
>>> David Feuer
>>> Well-Typed, LLP
>>>
>>> -------- Original message --------
>>> From: Harendra Kumar <harendra.kumar at gmail.com>
>>> Date: 2/4/18 10:50 PM (GMT-05:00)
>>> To: ghc-devs at haskell.org
>>> Subject: rolling span and groupBy for lists
>>>
>>> Hi,
>>>
>>> For a small problem, I was looking for a groupBy like function that
>>> groups
>>> based on a predicate on successive elements but I could not find one. I
>>> wrote these little functions for that purpose:
>>>
>>> -- | Like span, but with a predicate that compares two successive
>>> elements.
>>> The
>>> -- span ends when the two successive elements do not satisfy the
>>> predicate.
>>> rollingSpan :: (a -> a -> Bool) -> [a] -> ([a], [a])
>>> rollingSpan _ xs@[] = (xs, xs)
>>> rollingSpan _ xs@[_] = (xs, [])
>>> rollingSpan p (x1:xs@(x2:_))
>>>     | p x1 x2 =
>>>         let (ys, zs) = rollingSpan p xs
>>>         in (x1 : ys, zs)
>>>     | otherwise = ([x1], xs)
>>>
>>> -- | Like 'groupBy' but with a predicate that compares two successive
>>> elements.
>>> -- A group ends when two successive elements do not satisfy the
>>> predicate.
>>> rollingGroupBy :: (a -> a -> Bool) -> [a] -> [[a]]
>>> rollingGroupBy _ [] = []
>>> rollingGroupBy cmp xs =
>>>     let (ys, zs) = rollingSpan cmp xs
>>>     in ys : rollingGroupBy cmp zs
>>>
>>> Are there any existing functions that serve this purpose or is there any
>>> simpler way to achieve such functionality? If not, where is the right
>>> place
>>> for these, if any. Can they be included in Data.List in base?
>>>
>>> Thanks,
>>> Harendra
>>>
>>
>>
>>
>>
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>
>
>
> --
> Markus Läll
>
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