{-# LANGUAGE LambdaCase, ScopedTypeVariables, TypeApplications #-}
import Control.Exception (throwIO)
import Control.Monad (when)
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.Writer (execWriterT, tell)
import Data.Foldable (for_)
import Data.List (isPrefixOf)
import Data.Typeable (Typeable)
import qualified Language.Haskell.Interpreter as Hint

-- |
-- Interpret expressions into values:
--
-- >>> eval @[Int] "[1,2] ++ [3]"
-- Right [1,2,3]
-- 
-- Send values from your compiled program to your interpreted program by
-- interpreting a function:
--
-- >>> Right f <- eval @(Int -> [Int]) "\\x -> [1..x]"
-- >>> f 5
-- [1,2,3,4,5]
eval :: forall t. Typeable t
     => String -> IO (Either Hint.InterpreterError t)
eval s = Hint.runInterpreter $ do
  Hint.setImports ["Prelude"]
  Hint.interpret s (Hint.as :: t)

-- |
-- >>> :{
-- do Right contents <- browse "Prelude"
--    for_ contents $ \(identifier, tp) -> do
--      when ("put" `isPrefixOf` identifier) $ do
--        putStrLn $ identifier ++ " :: " ++ tp
-- :}
-- putChar :: Char -> IO ()
-- putStr :: String -> IO ()
-- putStrLn :: String -> IO ()
browse :: Hint.ModuleName -> IO (Either Hint.InterpreterError [(String, String)])
browse moduleName = Hint.runInterpreter $ do
  Hint.setImports ["Prelude", "Data.Typeable", moduleName]
  exports <- Hint.getModuleExports moduleName
  execWriterT $ do
    for_ exports $ \case
      Hint.Fun identifier -> do
        tp <- lift $ Hint.typeOf identifier
        tell [(identifier, tp)]
      _ -> pure ()  -- skip datatypes and typeclasses