Re: [Haskell-cafe] Automatically generate sum type members -> [String]

Also there is good article by Chris Done: http://chrisdone.com/posts/data-typeable. Hope this will be helpful. вт, 19 мая 2015 г. в 5:20, Adam Bergmark :

Using GHC Generics: http://hackage.haskell.org/package/generic-deriving-1.7.0/docs/Generics-Deri...

On Tue, May 19, 2015 at 1:29 AM, Tikhon Jelvis wrote:

...

You can get this information through the Data.Data module. There are two typeclasses which can be (have to be, I believe) derived for your data type, Data and Typeable. The Data class lets you access a representation of your type including type constructors.

To set this up, you need to import Data.Data and enable the DeriveDataTypeable extension:

{-# LANGUAGE DeriveDataTypeable #-} import Data.Data

data Codes = A0100A | A0500A deriving (Show, Data, Typeable)

Now you can get a representation of the type:

λ> dataTypeOf (undefined :: Codes) DataType {tycon = "Main.Codes", datarep = AlgRep [A0100A,A0500A]}

Since your type is an algebraic data type (AlgRep), the DataRep contains its constructors, which you can inspect with functions from the Data.Data module.

On Mon, May 18, 2015 at 4:20 PM, Cody Goodman < codygman.consulting@gmail.com> wrote:

...

Can I use either template Haskell, GHC Generics, or something else to get the list of Constructors in Codes? Then I could do `map show codeSumTypeMembers` and get `["A0100A","A0500A"]`?

Here's an example of solving this problem manually:

data Codes = A0100A | A0500A deriving Show

codeExists "A0100A" = True codeExists "A0500A" = True codeExists _ = False

main = print $ codeExists xmlElementName where xmlElementName = "A0500A"

-- λ> main -- True _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

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