Re: [Haskell-cafe] Object oriented haskell.

How would setting/modification work in your scheme? This problem has been solved a couple of times within the Haskell community and you're most likely looking for a lens library. They make data accessors first class and a subset of them compose in a way that reads just like object oriented notation. For example, with `lens` you can do the following: data MyState = MyState { _person :: Person } data Person = Person { _pos :: (Int, Int) } makeLenses [''MyState, ''Person] (person.pos._1 += 1) :: State MyState () Notice that the lenses compose with (.), compose in the order you expect from OO programming (and opposite normal function composition -- though it's actually the same), and allow you to set (as well as view). The `lens` package also provides these lenses for most of base along with many other useful tools for this kind of programming (notice _1 that acts as an accessor into a tuple). On Thu, May 15, 2014 at 1:44 PM, Kyle Marek-Spartz < kyle.marek.spartz@gmail.com> wrote:

Recently, on LtU: http://lambda-the-ultimate.org/node/4951

Most relevantly: https://ghc.haskell.org/trac/ghc/wiki/Records/DeclaredOverloadedRecordFields...

– Kyle Marek-Spartz

On May 15, 2014, 12:38:29 PM, silvio wrote: ------------------------------

Hi Haskell,

I've been wondering if (.) is so cool in other languages why can't we make it even cooler in haskell. And went on to implement such a (.) based on multiparameter type classes and type families.

type family Output object action class Action object action where (.) :: object -> action -> Output object action

I'm not sure if this has been done before like this but i didn't find anything. I used Map as an example, and here is what I ended up with:

...

:m -Prelude import Prelude hiding ((.)) import Object import Object.Example import Data.Map hiding (size) let m = empty . [ 'f' := Just 1, 'o' := Just 2, 'o' := Nothing ] m fromList [('f',Just 1),('o',Nothing)] m . 'f' Just 1 m . size 2

I also have a pretty cool (almost) solution to the name collision problem.

Visit the project homepage for a more thorough explanation.

https://github.com/yokto/object

And to those who gonna hate on me because they like the (.) as function composition I have only this to say.

type instance Output (b -> c) (a -> b') = (a -> c) instance (b ~ b') => Action (b -> c) (a -> b') where f . g = f Prelude.. g

Have fun,

Silvio _______________________________________________ Haskell-Cafe mailing list mailto:Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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