simple collection of meta information via Data/Generics

GenFoo.hs

{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}

module Foo where

import GHC.Generics
import Data.Data

newtype FooT = FooD Int deriving (Generic, Data, Typeable)

someFoo :: FooT
someFoo = FooD 7

{- We can use generics to get the constructor name from someFoo,
 - as well as internal constructor information:

   *Foo >let (_,types) = runWriter $ gmapM (\d -> tell [typeOf d] >> return d)
   someFoo
   *Foo>> :t types
   types :: [TypeRep]
   *Foo> types
   [Int]

 -}

{- We can use getConName on the rep generated from someFoo as well
 -
   *Foo GHC.Generics> getConName $ from someFoo 
   "FooD"
 -}
class GConName a where
    getConName :: a -> String

instance (GConName (b c)) => GConName (M1 D a b c) where
    getConName (M1 x) = getConName x

instance Constructor a => GConName (M1 C a b c) where
    getConName = conName

-- a full Generic class would typically have more instances.