Proposal for Data.List.splitBy
Marcus D. Gabriel
marcus at gabriel.name
Mon Jan 19 15:45:38 EST 2009
Brent Yorgey wrote:
> Not really. You are welcome to look at the source of
> Data.List.Split.Internals yourself;
Fair enough, I will look at it.
> Let me be clear---I am not against adding some splitting functions to
> Data.List, if consensus as to what these functions should be is
Not to worry, this was clear to me. I am sorry if my thread obscured this.
> If I were to write
> organizeBy :: ([a] -> Bool) -> [a] -> [([a], [a])]
> could you think of a specification such that this function
> would be a work horse in implementing Data.List.Split.Internals
> and Data.List.Split?
> I could, but I think the result would be rather uglier and harder to
> understand than the current implementation.
I understand. I do not perceive that I have expressed very well the way
that I am trying to conceptualise of this, but the observation of yours
above makes me conclude that adding a few splitter functions to
Data.List would just be arbitrary. (Alex already stated this point of
> Finally, this whole thread brings up the question in my mind
> about module design. As work is put into Data.List.Split, what
> is the guiding principle that prevents it from becoming
> Data.List.Extensions or to be a bit more direct,
> Are you serious?
Well, actually yes, I was serious, but see below.
> It seems quite clear to me that Data.List.Split will
> *not* turn into that. For one thing, it contains only list-splitting
> functions; for another thing, I do not foresee putting that much more
> work into it.
Ok, I was on a tangent. Given this above, no, I was not serious.
> A theoretical module which contains implementations/combinators for
> implementing every possible method of list-splitting known to man.
> This way no one has to argue about what the correct interface for
> split is, we can just have them all.
>> Is not this Data.List? In other words, what idea or theme does
>> a new Haskell programmer use to decide to first look into Data.List
>> as opposed to Data.List.Split and vice versa?
> I was being sort of facetious in that quote. =)
Ok, once again, I was on a tangent and drifting off topic. In my
defence, my parents-in-law were here for my Son's birthday which in
Alsace means a lot of good food and wine which also means I should not
write e-mails at night after such an event :).
So, to conclude, when I first started using Haskell 98, at one point in
time I was looking for some splitter idioms in the List module. The
functions break and span were close, but not it. The functions
> lines :: String -> [String]
> unlines :: [String] -> String
> words :: String -> [String]
> unwords :: [String] -> String
seemed out of place compared to everything else in the List module just
because of their type signature whereupon it seemed even more odd that I
could not just split /etc/passwd or /etc/group on ':' with something
directly suited to the task that was in the List module as an example.
Thanks for the thread,
Marcus D. Gabriel, Ph.D. Saint Louis, FRANCE
http://www.marcus.gabriel.name mailto:marcus at gabriel.name
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