ghc-mod/NotCPP/LookupValueName.hs
2016-02-04 10:54:55 -08:00

45 lines
1.3 KiB
Haskell

{-# LANGUAGE CPP #-}
{-# LANGUAGE TemplateHaskell #-}
-- | This module uses scope lookup techniques to either export
-- 'lookupValueName' from @Language.Haskell.TH@, or define
-- its own 'lookupValueName', which attempts to do the
-- same job with just 'reify'. This will sometimes fail, but if it
-- succeeds it will give the answer that the real function would have
-- given.
--
-- The idea is that if you use lookupValueName from this module,
-- your client code will automatically use the best available name
-- lookup mechanism. This means that e.g. 'scopeLookup' can work
-- very well on recent GHCs and less well but still somewhat
-- usefully on older GHCs.
module NotCPP.LookupValueName (
lookupValueName
) where
import Language.Haskell.TH
import NotCPP.Utils
bestValueGuess :: String -> Q (Maybe Name)
bestValueGuess s = do
mi <- maybeReify (mkName s)
case mi of
Nothing -> no
Just i -> case i of
#if __GLASGOW_HASKELL__ >= 800
VarI n _ _ -> yes n
DataConI n _ _ -> yes n
#else
VarI n _ _ _ -> yes n
DataConI n _ _ _ -> yes n
#endif
_ -> err ["unexpected info:", show i]
where
no = return Nothing
yes = return . Just
err = fail . showString "NotCPP.bestValueGuess: " . unwords
$(recover [d| lookupValueName = bestValueGuess |] $ do
VarI{} <- reify (mkName "lookupValueName")
return [])