Transparent type annotations in Haskell

main.hs

{-# LANGUAGE DataKinds       #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeOperators   #-}

import           Meta

data R = R
    { bravo   :: Bool
    , charlie :: Char // "Charlie docs"
    }

$(mkMeta 'charlie)
-- meta_charlie = "LitT (StrTyLit \"Charlie docs\")"

main :: IO ()
main = putStrLn meta_charlie

Meta.hs

{-# LANGUAGE PolyKinds       #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeOperators   #-}

module Meta where

import           Control.Monad
import           Language.Haskell.TH

type a // b = a

mkMeta name = do
    VarI _ typ _ <- reify name
    let AppT _record (AppT (AppT (ConT con) _field) ann) = typ
    unless (con == ''(//)) $
        fail $ show con
    let metaName = mkName $ "meta_" <> nameBase name
    [d| $(varP metaName) = $(stringE $ show ann) |]