Re: [Haskell-cafe] extensible records - Vinyl - alternatives?

Hi Peter, If you compare the two, you can see that some parts are nearly the same: ::: ~ Tagged :& ~ HCons RNil ~ HNil The labels aren't there at runtime in either library, since the label that is part of ::: (or Tagged) is missing from the data constructor (ie. it is a phantom type). But you can still define functions that depend on the type of a record: see the Show instances of either record type for example. So in some weak sense you have the same "runtime information of labels" in both libraries. Regards, Adam On Mon, May 5, 2014 at 3:21 AM, Peter Althainz wrote:

Hi Adam,

thanks for your answer, I will re-check HList with Labelable labels. With regards to your question "named labels": good point, all records indeed have "named labels" so what was my statement? I actually thought that Vinyl does keep run-time information of the labels from a Blog about vinyl-gl, but actually I'm not so sure about it anymore, so it is more a question: do those alternatives of extensible records differentiate by the way they keep runtime information of labels?

regards Peter

2014-05-03 18:54 GMT+02:00 adam vogt :

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Hello Peter,

Could you show what you mean by "named labels"?

Vinyl is a fine choice, but have you looked at HList >= 0.3? The lenses/labels done with Data.HList.Labelable are prettier than the vinyl alternative in my biased opinion. Furthermore, they support changing types in the record unlike vinyl (ie. they provide a Lens not Lens').

HList is a bit slow at compile time http://code.haskell.org/~aavogt/HList-benchmark/a.html if you make records with many fields. That situation may improve soon if we take advantage of the ordering on Symbol that ghc-7.8 introduced. In other words, we will probably follow the lead of http://www.haskell.org/haskellwiki/CTRex and make Records sorted by their labels.

There are quite a few other libraries

http://www.haskell.org/haskellwiki/Extensible_record#Libraries_on_hackage. Also consider lens' makeClassy as another solution to the records problem.

Regards, Adam

On Sat, May 3, 2014 at 6:16 AM, Peter Althainz wrote:

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Dear All,

I'm searching a handsome library for handling large amounts of configuration data in a flexible manner. So to speak I want to use some kind of inheritance of data fields. I think this is where the extensible records discussion is a proper description of my use case.

I've found 2 libraries making this work, so far:

HList Vinyl

I currently prefer Vinyl due to the complex types in HList, lens compatibiliy, named labels. (I love the HList and OOHaskel papers, but for practical use, I currently prefer Vinyl).

What do you think, what is the best way nowadays to use extensible records? Is Vinyl a good choice from your point of view?

regards Peter

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