Proposal reminder: Add functions to get consecutive elements to Data.List

[Johan Holmquist]

Also these two were mentioned earlier (using zipConsecutivesWith):

    -- fibonacci:
    fibs = 1 : 1 : zipConsecutivesWith (+) fibs

    -- get the edges of a closed path defined by points (ps):
    edges ps = zipConsecutivesWith makeEdge (ps ++ take 1 ps)

There are two things to decide:

1. Whether this should indeed be added to base (Data.List)
2. What names we should use in case of inclusion in base

The proposed functions are:

    zipConsecutives :: [a] -> [(a,a)]

and

    zipConsecutivesWith :: (a -> a -> b) -> [a] -> [b]

I would not object to some shorter names, such as zipConsecs,
zipConsecsWith etc...

2016-05-19 7:37 GMT+02:00 David Feuer <david.feuer at gmail.com>:

> You promised a collection of use cases. I seem to have missed it. Could
> you send the link again?
> On May 19, 2016 1:35 AM, "Johan Holmquist" <holmisen at gmail.com> wrote:
>
>> The discussion period for this proposal is near (31 of May).
>>
>> So far I count 1 for and 2 against the proposal.
>>
>> Joachim Breitner made a good enumeration of some advantages of adding
>> these to base. Here is an enumeration of pros:
>>
>> * Availability in Data.List gives this pattern a common name.
>>
>> * A common name for this makes code easier to read and decreases the risk
>> of getting the definition wrong.
>>
>> * The argument won't have to be repeated, hence making it easier to chain
>> the functions.
>>
>> * List-fusion potential.
>>
>>
>> Tobias Florek pointed out that `zip <*> tail` can be used to define this
>> inline without the need for repeating the argument and made a reference to
>> the Fairbairn threshold. This is elegant, but I am afraid that people might
>> consider this obscure code golfing if used.
>>
>> Cheers
>> Johan Holmquist
>>
>>
>> ---------- Forwarded message ----------
>> From: Henning Thielemann <lemming at henning-thielemann.de>
>> Date: 2016-04-13 13:28 GMT+02:00
>> Subject: Re: Proposal: Add functions to get consecutive elements to
>> Data.List
>> To: Johan Holmquist <holmisen at gmail.com>
>> Cc: Haskell Libraries <libraries at haskell.org>
>>
>>
>>
>> On Wed, 13 Apr 2016, Johan Holmquist wrote:
>>
>> It is not strictly more general because it cannot handle empty sequences.
>>>
>>
>> Think of it as if it handles the non-[] case.
>>
>>
>> _______________________________________________
>> Libraries mailing list
>> Libraries at haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/libraries/attachments/20160519/f3c1e845/attachment-0001.html>