Haskell interpreter: using "return"

hint_return.hs

import Control.Monad
import Data.List
import Language.Haskell.Interpreter

main :: IO ()
main = do r <- runInterpreter testHint
          case r of
            Left err -> printInterpreterError err
            Right () -> putStrLn "that's all folks"

-- observe that Interpreter () is an alias for InterpreterT IO ()
testHint :: Interpreter ()
testHint = do
  setImportsQ [("Prelude", Nothing), ("Data.Map", Just "M"), ("Language.Haskell.Interpreter", Nothing)]

  res <- interpret "return $ show $ 10+2" (as:: InterpreterT IO String)
  res1 <- res
  say  res1
  say "Bye"


say :: String -> Interpreter ()
say = liftIO . putStrLn



printInterpreterError :: InterpreterError -> IO ()
printInterpreterError e = putStrLn $ "Ups... " ++ (show e)