Re: [Haskell-cafe] Helper classes for Generics
Hi Reiner, It is indeed not strictly necessary to define such helper classes for kind * generic functions. You do need them for kind * - * functions, though. Also, I think they should always be used because they help keep things separate. If we use an implementation of generics with DataKinds [1], then the helper classes always have a different kind from the user-facing classes. Cheers, Pedro [1] http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/GenericDeriving#Kindpolymorphicoverhaul On Mon, Mar 12, 2012 at 04:27, Reiner Pope reiner.p...@gmail.com wrote: Hi all, I've been playing with GHC's new generics features (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html). All the documentation I've seen suggests creating a helper class -- for instance, the GSerialize class in the above link -- on which one defines generic instances. It seems to me that this isn't necessary. For example, here's the the example from the GHC docs, but without a helper class: -- set the phantom type of Rep to (), to avoid ambiguity from0 :: Generic a = a - Rep a () from0 = from data Bit = O | I class Serialize a where put :: a - [Bit] default put :: (Generic a, Serialize (Rep a ())) = a - [Bit] put = put . from0 instance Serialize (U1 x) where put U1 = [] instance (Serialize (a x), Serialize (b x)) = Serialize ((a :*: b) x) where put (x :*: y) = put x ++ put y instance (Serialize (a x), Serialize (b x)) = Serialize ((a :+: b) x) where put (L1 x) = O : put x put (R1 x) = I : put x instance (Serialize (a x)) = Serialize (M1 i c a x) where put (M1 x) = put x instance (Serialize a) = Serialize (K1 i a x) where put (K1 x) = put x Is there a reason to prefer using helper classes? Or perhaps we should update the wiki page (http://www.haskell.org/haskellwiki/Generics) to avoid using helper classes? Regards, Reiner ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Helper classes for Generics
I'd have a question concerning GHC.Generics: how does it relate to SYB's Data.Generics? Is it intended to replace it or complete it? In other words: does class Data.Generics.Data class do things that class GHC.Generics.Generic can't do? Le 12 mars 2012 04:27, Reiner Pope reiner.p...@gmail.com a écrit : Hi all, I've been playing with GHC's new generics features (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html). All the documentation I've seen suggests creating a helper class -- for instance, the GSerialize class in the above link -- on which one defines generic instances. It seems to me that this isn't necessary. For example, here's the the example from the GHC docs, but without a helper class: -- set the phantom type of Rep to (), to avoid ambiguity from0 :: Generic a = a - Rep a () from0 = from data Bit = O | I class Serialize a where put :: a - [Bit] default put :: (Generic a, Serialize (Rep a ())) = a - [Bit] put = put . from0 instance Serialize (U1 x) where put U1 = [] instance (Serialize (a x), Serialize (b x)) = Serialize ((a :*: b) x) where put (x :*: y) = put x ++ put y instance (Serialize (a x), Serialize (b x)) = Serialize ((a :+: b) x) where put (L1 x) = O : put x put (R1 x) = I : put x instance (Serialize (a x)) = Serialize (M1 i c a x) where put (M1 x) = put x instance (Serialize a) = Serialize (K1 i a x) where put (K1 x) = put x Is there a reason to prefer using helper classes? Or perhaps we should update the wiki page (http://www.haskell.org/haskellwiki/Generics) to avoid using helper classes? Regards, Reiner ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Helper classes for Generics
Hi Yves, GHC.Generics [1] and SYB [2] are two rather different approaches to generic programming. There are things that can be done in one but not in the other, and there are things that are easier on one rather than the other. For instance, SYB tends to be very useful for large AST transformations, with functions that have a general behaviour but a couple of particular cases for a few constructors. GHC.Generics, on the other hand, can encode functions such as generic fmap and traverse. It lends itself better to optimisation since it doesn't use runtime casts, and as such tends to be faster than SYB. It isn't planned to replace SYB. Cheers, Pedro [1] http://www.haskell.org/haskellwiki/Generics [2] http://www.cs.uu.nl/wiki/bin/view/GenericProgramming/SYB On Mon, Mar 12, 2012 at 16:35, Yves Parès yves.pa...@gmail.com wrote: I'd have a question concerning GHC.Generics: how does it relate to SYB's Data.Generics? Is it intended to replace it or complete it? In other words: does class Data.Generics.Data class do things that class GHC.Generics.Generic can't do? Le 12 mars 2012 04:27, Reiner Pope reiner.p...@gmail.com a écrit : Hi all, I've been playing with GHC's new generics features (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html). All the documentation I've seen suggests creating a helper class -- for instance, the GSerialize class in the above link -- on which one defines generic instances. It seems to me that this isn't necessary. For example, here's the the example from the GHC docs, but without a helper class: -- set the phantom type of Rep to (), to avoid ambiguity from0 :: Generic a = a - Rep a () from0 = from data Bit = O | I class Serialize a where put :: a - [Bit] default put :: (Generic a, Serialize (Rep a ())) = a - [Bit] put = put . from0 instance Serialize (U1 x) where put U1 = [] instance (Serialize (a x), Serialize (b x)) = Serialize ((a :*: b) x) where put (x :*: y) = put x ++ put y instance (Serialize (a x), Serialize (b x)) = Serialize ((a :+: b) x) where put (L1 x) = O : put x put (R1 x) = I : put x instance (Serialize (a x)) = Serialize (M1 i c a x) where put (M1 x) = put x instance (Serialize a) = Serialize (K1 i a x) where put (K1 x) = put x Is there a reason to prefer using helper classes? Or perhaps we should update the wiki page (http://www.haskell.org/haskellwiki/Generics) to avoid using helper classes? Regards, Reiner ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Helper classes for Generics
Thanks for the clarification. But could not class Data have been used for generic Deriving of classes? I imagine it would have been harder, but I fail to see if would have been possible... Le 12 mars 2012 16:58, José Pedro Magalhães j...@cs.uu.nl a écrit : Hi Yves, GHC.Generics [1] and SYB [2] are two rather different approaches to generic programming. There are things that can be done in one but not in the other, and there are things that are easier on one rather than the other. For instance, SYB tends to be very useful for large AST transformations, with functions that have a general behaviour but a couple of particular cases for a few constructors. GHC.Generics, on the other hand, can encode functions such as generic fmap and traverse. It lends itself better to optimisation since it doesn't use runtime casts, and as such tends to be faster than SYB. It isn't planned to replace SYB. Cheers, Pedro [1] http://www.haskell.org/haskellwiki/Generics [2] http://www.cs.uu.nl/wiki/bin/view/GenericProgramming/SYB On Mon, Mar 12, 2012 at 16:35, Yves Parès yves.pa...@gmail.com wrote: I'd have a question concerning GHC.Generics: how does it relate to SYB's Data.Generics? Is it intended to replace it or complete it? In other words: does class Data.Generics.Data class do things that class GHC.Generics.Generic can't do? Le 12 mars 2012 04:27, Reiner Pope reiner.p...@gmail.com a écrit : Hi all, I've been playing with GHC's new generics features (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html). All the documentation I've seen suggests creating a helper class -- for instance, the GSerialize class in the above link -- on which one defines generic instances. It seems to me that this isn't necessary. For example, here's the the example from the GHC docs, but without a helper class: -- set the phantom type of Rep to (), to avoid ambiguity from0 :: Generic a = a - Rep a () from0 = from data Bit = O | I class Serialize a where put :: a - [Bit] default put :: (Generic a, Serialize (Rep a ())) = a - [Bit] put = put . from0 instance Serialize (U1 x) where put U1 = [] instance (Serialize (a x), Serialize (b x)) = Serialize ((a :*: b) x) where put (x :*: y) = put x ++ put y instance (Serialize (a x), Serialize (b x)) = Serialize ((a :+: b) x) where put (L1 x) = O : put x put (R1 x) = I : put x instance (Serialize (a x)) = Serialize (M1 i c a x) where put (M1 x) = put x instance (Serialize a) = Serialize (K1 i a x) where put (K1 x) = put x Is there a reason to prefer using helper classes? Or perhaps we should update the wiki page (http://www.haskell.org/haskellwiki/Generics) to avoid using helper classes? Regards, Reiner ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Helper classes for Generics
It could, yes. Actually, using DefaultSignatures you can probably use SYB for defining classes with generic default methods, by adding Data and Typeable constraints instead of Generic. Cheers, Pedro 2012/3/12 Yves Parès yves.pa...@gmail.com Thanks for the clarification. But could not class Data have been used for generic Deriving of classes? I imagine it would have been harder, but I fail to see if would have been possible... Le 12 mars 2012 16:58, José Pedro Magalhães j...@cs.uu.nl a écrit : Hi Yves, GHC.Generics [1] and SYB [2] are two rather different approaches to generic programming. There are things that can be done in one but not in the other, and there are things that are easier on one rather than the other. For instance, SYB tends to be very useful for large AST transformations, with functions that have a general behaviour but a couple of particular cases for a few constructors. GHC.Generics, on the other hand, can encode functions such as generic fmap and traverse. It lends itself better to optimisation since it doesn't use runtime casts, and as such tends to be faster than SYB. It isn't planned to replace SYB. Cheers, Pedro [1] http://www.haskell.org/haskellwiki/Generics [2] http://www.cs.uu.nl/wiki/bin/view/GenericProgramming/SYB On Mon, Mar 12, 2012 at 16:35, Yves Parès yves.pa...@gmail.com wrote: I'd have a question concerning GHC.Generics: how does it relate to SYB's Data.Generics? Is it intended to replace it or complete it? In other words: does class Data.Generics.Data class do things that class GHC.Generics.Generic can't do? Le 12 mars 2012 04:27, Reiner Pope reiner.p...@gmail.com a écrit : Hi all, I've been playing with GHC's new generics features (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html). All the documentation I've seen suggests creating a helper class -- for instance, the GSerialize class in the above link -- on which one defines generic instances. It seems to me that this isn't necessary. For example, here's the the example from the GHC docs, but without a helper class: -- set the phantom type of Rep to (), to avoid ambiguity from0 :: Generic a = a - Rep a () from0 = from data Bit = O | I class Serialize a where put :: a - [Bit] default put :: (Generic a, Serialize (Rep a ())) = a - [Bit] put = put . from0 instance Serialize (U1 x) where put U1 = [] instance (Serialize (a x), Serialize (b x)) = Serialize ((a :*: b) x) where put (x :*: y) = put x ++ put y instance (Serialize (a x), Serialize (b x)) = Serialize ((a :+: b) x) where put (L1 x) = O : put x put (R1 x) = I : put x instance (Serialize (a x)) = Serialize (M1 i c a x) where put (M1 x) = put x instance (Serialize a) = Serialize (K1 i a x) where put (K1 x) = put x Is there a reason to prefer using helper classes? Or perhaps we should update the wiki page (http://www.haskell.org/haskellwiki/Generics) to avoid using helper classes? Regards, Reiner ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Helper classes for Generics
Hi all, I've been playing with GHC's new generics features (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html). All the documentation I've seen suggests creating a helper class -- for instance, the GSerialize class in the above link -- on which one defines generic instances. It seems to me that this isn't necessary. For example, here's the the example from the GHC docs, but without a helper class: -- set the phantom type of Rep to (), to avoid ambiguity from0 :: Generic a = a - Rep a () from0 = from data Bit = O | I class Serialize a where put :: a - [Bit] default put :: (Generic a, Serialize (Rep a ())) = a - [Bit] put = put . from0 instance Serialize (U1 x) where put U1 = [] instance (Serialize (a x), Serialize (b x)) = Serialize ((a :*: b) x) where put (x :*: y) = put x ++ put y instance (Serialize (a x), Serialize (b x)) = Serialize ((a :+: b) x) where put (L1 x) = O : put x put (R1 x) = I : put x instance (Serialize (a x)) = Serialize (M1 i c a x) where put (M1 x) = put x instance (Serialize a) = Serialize (K1 i a x) where put (K1 x) = put x Is there a reason to prefer using helper classes? Or perhaps we should update the wiki page (http://www.haskell.org/haskellwiki/Generics) to avoid using helper classes? Regards, Reiner___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
