On Tue, May 3, 2011 at 12:04 PM, Bryan O'Sullivan wrote:

On Tue, May 3, 2011 at 8:00 AM, Yitzchak Gale wrote:

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Could you please add a Semigroup instance for Text?

I'd strongly recommend writing an instance for the text package's Builder

type instead. Vastly more efficient for non-trivial jobs.

Unfortunately, I don't think I can really bring myself to do either. I was deliberately trying to keep the number of dependencies for the semigroups as low as possible in contrast to my previous efforts. In fact, I'll likely invert the dependencies from tagged and void, leaving only the dependency on containers, which is somewhat unavoidable, but still Haskell 98. My goal was to build a very small standardizable library. Data.Text requires dependencies that would take my package and a whole hierarchy of other Haskell 98 packages that are built on top of it, out of Haskell 98. -Edward

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Once you're doing that, I suppose you'd also want to add it for lazy Text and both kinds of ByteStrings.

Likewise, there's allegedly work afoot to write a builder for bytestrings.

On Tue, May 3, 2011 at 1:14 PM, Yitzchak Gale wrote:

You are quite right. These should really be defined in their respective packages. I don't think it's too onerous for them to add a dependency on semigroups, even before you reverse the few lightweight dependencies that semigroups has.

Unfortunately, the semigroups package will have to go into the Platform before either text or bytestring can make use of it. I think that would be great to have, but the getting from here to there is not necessarily fun.

On Tue, May 3, 2011 at 3:14 PM, Yitzchak Gale wrote:

I wrote:

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Could you please add a Semigroup instance for Text?

Edward Kmett wrote:

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Unfortunately, I don't think I can really bring myself to do either. I was deliberately trying to keep the number of dependencies for the semigroups as low as possible...

You are quite right. These should really be defined in their respective packages. I don't think it's too onerous for them to add a dependency on semigroups, even before you reverse the few lightweight dependencies that semigroups has.

Bryan O'Sullivan wrote:

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I'd strongly recommend writing an instance for the text package's Builder type instead. Vastly more efficient for non-trivial jobs.

Well, in my case, I'm iterating over many small Texts, slicing and dicing small groups of them in various ways to look for overlaps, and splicing the pieces back together in different combinations. It's quite fast as it is; what I'm looking for is to make the formulas look simpler and more understandable. I doubt that builders will be any help for that. Whereas using <> from semigroups instead of `T.append` or `mappend` is a huge help.

Can you locally define an operator (<>) for monoids?

Apart from my own use case, semigroups are a simple and fundamental idiom that I think will become much more widely used as people become more aware of them. Just like every Monad should have a Functor instance, every Monoid should have a Semigroup instance.

Thanks, Yitz

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