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

[Geraldus]

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 <adam at bergmark.nl>:

> Using GHC Generics:
> http://hackage.haskell.org/package/generic-deriving-1.7.0/docs/Generics-Deriving-ConNames.html
>
>
> On Tue, May 19, 2015 at 1:29 AM, Tikhon Jelvis <tikhon at jelv.is> 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 at 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
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>>
>>
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