On Sat, Feb 12, 2011 at 11:21:37AM -0500, Gwern Branwen wrote:

On Sat, Feb 12, 2011 at 11:00 AM, Robert Clausecker wrote:

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Is there any reason, that one can't find a function that splits a list at a seperator in the standard library? I imagined something like this:

   splitSeperator :: Eq a => a -> [a] -> [[a]]

   splitSeperator ',' "foo,bar,baz"      --> ["foo","bar","baz"]

Or something similar? This is needed so often, even if I can implement it in one line, is there any reason why it's not in the libs?

See http://hackage.haskell.org/package/split

The reason it's not in Data.List is because there are a bazillion different splits one might want (when I was pondering the issue before Brent released it, I had collected something like 8 different proposed splits), so no agreement could ever be reached.

It is curious though that the Python community managed to agree on a single implementation and include that in the standard library… So it is possible :) I also needed a split function and ended up with coding one that behaves like the Python one for my project. regards, iustin

On Sun, Feb 13, 2011 at 06:01:01PM +0800, Lyndon Maydwell wrote:

Does the Python implementation operate on Strings, or all lists?

Of course, just on strings.

I think this could be quite important as many split implementations take regular expressions as arguments. This could be quite challenging for general lists.

Agreed. But (in Python at least), split via re and split via (static) element are two separate functions, and split via element can be nicely replicated in Haskell. regards, iustin

That said, I would like to see some of these features in the split package.

On Sun, Feb 13, 2011 at 5:50 PM, Iustin Pop wrote:

...

On Sat, Feb 12, 2011 at 11:21:37AM -0500, Gwern Branwen wrote:

...

On Sat, Feb 12, 2011 at 11:00 AM, Robert Clausecker wrote:

...

Is there any reason, that one can't find a function that splits a list at a seperator in the standard library? I imagined something like this:

   splitSeperator :: Eq a => a -> [a] -> [[a]]

   splitSeperator ',' "foo,bar,baz"      --> ["foo","bar","baz"]

Or something similar? This is needed so often, even if I can implement it in one line, is there any reason why it's not in the libs?

See http://hackage.haskell.org/package/split

The reason it's not in Data.List is because there are a bazillion different splits one might want (when I was pondering the issue before Brent released it, I had collected something like 8 different proposed splits), so no agreement could ever be reached.

It is curious though that the Python community managed to agree on a single implementation and include that in the standard library… So it is possible :)

I also needed a split function and ended up with coding one that behaves like the Python one for my project.

regards, iustin

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On Sun, Feb 13, 2011 at 11:21:42AM +0100, Henning Thielemann wrote:

On Sun, 13 Feb 2011, Iustin Pop wrote:

...

On Sat, Feb 12, 2011 at 11:21:37AM -0500, Gwern Branwen wrote:

...

See http://hackage.haskell.org/package/split

The reason it's not in Data.List is because there are a bazillion different splits one might want (when I was pondering the issue before Brent released it, I had collected something like 8 different proposed splits), so no agreement could ever be reached.

It is curious though that the Python community managed to agree on a single implementation and include that in the standard library… So it is possible :)

It was not the implementation, that was discussed in length, but it was the question, what 'split' shall actually do.

Doh, of course I meant they managed to agree on a single definition of what split means. Sorry for bad wording.

If you are satisfied with a simple Haskell 98 implementation of a 'split' operation you might like 'chop' in http://hackage.haskell.org/packages/archive/utility-ht/0.0.5.1/doc/html/Data...

Probably, but when I can have my own version in ~4 lines of Haskell, I'd rather not have another dependency (that might or might not be packaged in my distro). regards, iustin

On Mon, Feb 14, 2011 at 07:52, Evan Laforge wrote:

the simple 'join :: String -> [String] -> String' and 'split :: String -> String -> [String]' versions work in enough cases.

BTW, this "join" is Data.List.intercalate. --Max

On Sun, Feb 13, 2011 at 11:33:16PM -0800, Donn Cave wrote:

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It is curious though that the Python community managed to agree on a single implementation and include that in the standard library

To me, it's more like 2 implementations, overloaded on the same function name.

Python 2.6.2 (r262:71600, Aug 30 2009, 15:41:32) [GCC 2.95.3-haiku-090629] on haiku1 Type "help", "copyright", "credits" or "license" for more information.

...

...

...

import string string.split(' ho ho ') ['ho', 'ho'] string.split(' ho ho ', ' ') ['', 'ho', 'ho', '']

I.e., let the separator parameter default (to whitespace), and you get what we have with Prelude.words, but specify a split character and you get a reversible split. It wasn't a new idea, the Bourne shell for example has a similar dual semantics depending on whether the separator is white space or not. Somehow doesn't seem right for Haskell, though.

Agreed, but I don't think that lacking a generic split functionality (as in reversible split) is also good. iustin

Quoth Peter Simons , ...

having a dictator is not a necessary prerequisite for the ability to make decisions. It's quite possible to decide controversial matters without a dictator -- say, by letting people vote.

The problem might be slightly miscast here, as an inability to reach a decision in the face of controversy, and overall I don't think you could make much of a case that Python's development is noticeably more decisive. If you really have 8 candidates for the semantics of separator-split, then even if everyone can bring themselves to agree on one, it's still just one, out of 8 missing functions, and it's fairly understandable that this might not be very appealing. Python also - is different in that function semantics can be conveniently overloaded (I forgot the "count" parameter, I often want that one - split at the first (n - 1) locations and leave the remainder intact) - is different as a general matter of style and niche - doesn't have our division between String and ByteString - makes it harder and more expensive to implement string.split() Anyway, before it gets to the point where the crowds are camping in the city square and demanding a vote, it might be interesting to see where the code comes down on the matter, so I looked at the hackage source I already happen to have at hand, a measly 252 Haskell source files. I found one (1) separator-split implementation. I was surprised at so few, as I've done it myself several times, so maybe I happen to have an unrepresentative sample? Donn