@hackage modulespection0.1.2.2

Collect all of the declarations in a module using Template Haskell (via the GHC API).

One can either get all the names, or just the declarations (only type declarations are supported right now).

Here is a quick example:

import Language.Haskell.TH.Module.Magic (names)

data Test = Test Int
newtype OtherTest = OtherTest Test

someFunction :: String -> String
someFunction = id

-- 'names' is Template Haskell function that will collect all of the
-- toplevel declaration names of the current file.
names >>= runIO . print >> return []

Which will spew the following when compiling:

[Test,OtherTest,someFunction]

There is also declarations which can be used, for example, to make sure that all types have ToJSON/FromJSON instances.

import Data.Aeson.TH (deriveJSON, defaultOptions)
import MonadUtils (concatMapM)
import Language.Haskell.TH.Module.Magic (declarations)

data Test = Test Int
newtype OtherTest = OtherTest Test

concatMapM (deriveJSON defaultOptions) =<< declarations

Which will make JSON instances for Test, OtherTest and any other types added to the file.

You can also do the same thing for an existing module.

import Data.Aeson.TH (deriveJSON, defaultOptions)
import MonadUtils (concatMapM)
import Language.Haskell.TH.Module.Magic (moduleDeclarations)
import Data.Monoid

concatMapM (deriveJSON defaultOptions) =<< moduleDeclarations "Data.Monoid"

Which will build instances for all the types in Data.Monoid.