Re: Proposal: Add a splitBy / splitOn in Data.List

What about just adding Data.List.Split to base? -- Dan Burton On Fri, Nov 2, 2018 at 8:56 AM Elliot Cameron wrote:

I didn't realize cabal now supported scripting. I suppose that addresses a large number of my use cases for having this.

I didn't mean choosing different delimiters but only a single multielement delimiter, albeit that is also not flexible. If we also had a multicharacter replace function then a single-element split would be more tolerable.

I'm still in favor of providing one or two of the most common, most flexible versions of this just to help newcomers from other languages that have these functions in their standard libraries, but my opinion is not very strongly held.

On Fri, Nov 2, 2018, 8:18 AM Theodore Lief Gannon

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If you accept more than one delimiter but drop them, you've lost info about which one caused each break and can't map them back. It's more generic to keep them, since you can still filter.

On Fri, Nov 2, 2018, 4:39 AM Elliot Cameron

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Despite these subtleties, I must confess I've often wanted to whip up a quick script and been frustrated that these functions are missing from base. For example using Haskell as a sed/awk alternative can be pleasant *if* the functions you need are in base. What's more, in many years I've only really wanted one or two versions of this.

What if we added the most flexible of versions and included only that? This version would accept multicharacter delimiters, always throw them away, and always produce a new entry in the result for every occurrence of the delimiter. If you don't want the empty entries, you can filter. If you don't want leading, you can dropWhile. If you want the delimiters back, you can map. This seems like a nice trade-off for just being available in base.

On Fri, Nov 2, 2018, 1:51 AM Edward Kmett

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The main thing that prevented it from going into base is the number of subtleties about what precisely it means to properly "split" something.

Most languages make fairly arbitrary calls on topics such as:

* Do you split on list elements (e.g. ',') or list of elements, so you can multi-character delimiters ", "? What about multiple types of thing that are all delimiters, e.g. any whitespace character? * What do you do with the delimiters? * What happens with runs of delimiters? * What about initial or final runs of delimiters (e.g. leading spaces)?

The end result was that a split package was written by Brent Yorgey back in 2008 or so that rather comprehensively covers the design space, and it was incorporated into the Haskell Platform.

http://hackage.haskell.org/package/split-0.2.3.3/docs/Data-List-Split.html

-Edward

On Thu, Nov 1, 2018 at 1:34 PM Saurabh Nanda wrote:

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This has certainly been discussed before. A quick Google search turned up the following past discussions:

- https://mail.haskell.org/pipermail/libraries/2006-July/005494.html - https://mail.haskell.org/pipermail/libraries/2012-July/018228.html

Is there anything blocking this discussion & implementation? Anything that can be done to unblock it?

-- Saurabh.

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