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import Control.Monad
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
say "Load SomeModule.hs"
loadModules ["SomeModule.hs"]
--
say "Put the Prelude, Data.Map and *SomeModule in scope"
say "Data.Map is qualified as M!"
setTopLevelModules ["SomeModule"]
setImportsQ [("Prelude", Nothing), ("Data.Map", Just "M")]
--
say "Now we can query the type of an expression"
let expr1 = "M.singleton (f, g, h, 42)"
say $ "e.g. typeOf " ++ expr1
say =<< typeOf expr1
--
say $ "Observe that f, g and h are defined in SomeModule.hs, " ++
"but f is not exported. Let's check it..."
exports <- getModuleExports "SomeModule"
say (show exports)
--
say "We can also evaluate an expression; the result will be a string"
let expr2 = "length $ concat [[f,g],[h]]"
say $ concat ["e.g. eval ", show expr1]
a <- eval expr2
say (show a)
--
say "Or we can interpret it as a proper, say, int value!"
a_int <- interpret expr2 (as :: Int)
say (show a_int)
--
say "This works for any monomorphic type, even for function types"
let expr3 = "\\(Just x) -> succ x"
say $ "e.g. we interpret " ++ expr3 ++
" with type Maybe Int -> Int and apply it on Just 7"
fun <- interpret expr3 (as :: Maybe Int -> Int)
say . show $ fun (Just 7)
--
say "And sometimes we can even use the type system to infer the expected type (eg Maybe Bool -> Bool)!"
bool_val <- (interpret expr3 infer `ap` (return $ Just False))
say (show $ not bool_val)
--
say "Here we evaluate an expression of type string, that when evaluated (again) leads to a string"
res <- interpret "head $ map show [\"Worked!\", \"Didn't work\"]" infer >>= flip interpret infer
say res
say :: String -> Interpreter ()
say = liftIO . putStrLn
printInterpreterError :: InterpreterError -> IO ()
printInterpreterError e = putStrLn $ "Ups... " ++ (show e)
|
