{-----------------------------------------------------------------------------
HyperHaskell
------------------------------------------------------------------------------}
{-# LANGUAGE CPP #-}
{-# LANGUAGE GADTSyntax, ExistentialQuantification, RankNTypes, ScopedTypeVariables #-}
{-# LANGUAGE OverloadedStrings #-}
module Main where
import Control.Concurrent
import Control.DeepSeq
import Control.Monad
import Control.Monad.Catch
import Control.Exception (AsyncException(UserInterrupt), evaluate)
import Data.Typeable
import Text.Read (readMaybe)
import System.Environment as System
-- Haskell interpreter
import Language.Haskell.Interpreter hiding (eval, setImports)
import qualified Language.Haskell.Interpreter as Hint
-- web
import Data.Aeson (toJSON, (.=))
import qualified Data.Aeson as JSON
import qualified Data.ByteString.Char8 as B
import Data.Text (Text)
import Data.String (fromString)
import Web.Scotty
-- Interpreter
import Hyper.Internal
say = putStrLn
{-----------------------------------------------------------------------------
Main
------------------------------------------------------------------------------}
defaultPort :: Int
defaultPort = 8024
main :: IO ()
main = do
env <- System.getEnvironment
let port = maybe defaultPort id $ readMaybe =<< Prelude.lookup "PORT" env
(hint, interpreterLoop) <- newInterpreter
forkIO $ scotty port (jsonAPI hint)
interpreterLoop -- See NOTE [MainThread]
{- NOTE [MainThread]
We fork the web server and run GHC in the main thread.
This is because GHC registers handlers for signals like SIGTERM,
but for some reason, these handlers only work correctly if GHC
also has the main thread.
-}
{-----------------------------------------------------------------------------
Exported JSON REST API
------------------------------------------------------------------------------}
jsonAPI :: Hint -> ScottyM ()
jsonAPI hint = do
post "/cancel" $ do
liftIO $ cancel hint
json $ JSON.object [ "status" .= t "ok" ]
post "/setImports" $
json . result =<< liftIO . setImports hint =<< param "query"
post "/loadFiles" $
json . result =<< liftIO . loadFiles hint =<< param "query"
post "/eval" $ do
json . result =<< liftIO . eval hint =<< param "query"
t s = fromString s :: Text
result :: JSON.ToJSON a => Result a -> JSON.Value
result (Left e) = JSON.object [ "status" .= t "error", "errors" .= err e]
where
err e = toJSON $ case e of
UnknownError s -> [t s]
WontCompile xs -> map (t . errMsg) xs
NotAllowed s -> [t s]
GhcException s -> [t s]
result (Right x) = JSON.object [ "status" .= t "ok", "value" .= toJSON x ]
instance JSON.ToJSON Graphic where
toJSON g = JSON.object [ "type" .= t "html", "value" .= gHtml g ]
{-----------------------------------------------------------------------------
Exported interpreter functions
------------------------------------------------------------------------------}
setImports :: Hint -> [String] -> IO (Result ())
loadFiles :: Hint -> [FilePath] -> IO (Result ())
eval :: Hint -> String -> IO (Result Graphic)
-- NOTE: We implicitely load the Prelude and Hyper modules
setImports hint = run hint . Hint.setImports
. (++ ["Prelude", "Hyper"]) . filter (not . null)
loadFiles hint = run hint . Hint.loadModules . filter (not . null)
eval hint expr = run hint $ do
-- NOTE: We wrap results into an implicit call to Hyper.display
m <- Hint.interpret ("Hyper.displayIO " ++ Hint.parens expr) (as :: IO Graphic)
liftIO $ do
g <- m
evaluate (force g) -- See NOTE [EvaluateToNF]
{- NOTE [EvaluateToNF]
We evaluate the result in the interpreter thread to full normal form,
because it may be that this evaluation does not terminate,
in which case the user is likely to trigger a `UserInterrupt` asynchronous exception.
But this exception is only delivered to and handled by the interpreter thread.
Otherwise, the web server would be stuck trying to evaluate the result
in order to serialize it, with no way for the user to interrupt this.
-}
{-----------------------------------------------------------------------------
Interpreter Backend
------------------------------------------------------------------------------}
type Result a = Either InterpreterError a
toInterpreterError :: SomeException -> InterpreterError
toInterpreterError e = case fromException e of
Just e -> e
Nothing -> UnknownError (displayException e)
#if MIN_VERSION_base(4,8,0)
#else
displayException :: SomeException -> String
displayException = show
#endif
-- | Haskell Interpreter.
data Hint = Hint
{ run :: forall a. Interpreter a -> IO (Result a)
, cancel :: IO ()
}
data Action where
Action :: Interpreter a -> MVar (Result a) -> Action
debug s = liftIO $ putStrLn s
-- | Create and initialize a Haskell interpreter.
newInterpreter :: IO (Hint, IO ()) -- ^ (send commands, interpreter loop)
newInterpreter = do
vin <- newEmptyMVar
evalThreadId <- newEmptyMVar -- ThreadID of the thread responsible for evaluation
let
handler :: Interpreter ()
handler = do
debug "Waiting for Haskell expression"
Action ma vout <- liftIO $ takeMVar vin
let right = liftIO . putMVar vout . Right =<< ma
let left = liftIO . putMVar vout . Left . toInterpreterError
debug "Got Haskell expression, evaluating"
right `catch` left
debug "Wrote result"
run :: Interpreter a -> IO (Result a)
run ma = do
vout <- newEmptyMVar
putMVar vin (Action ma vout)
a <- takeMVar vout
case a of
Right _ -> return ()
Left e -> debug $ show e
return a
cancel :: IO ()
cancel = do
t <- readMVar evalThreadId
throwTo t UserInterrupt
-- NOTE: `throwTo` may block if the thread `t` has masked asynchronous execptions.
debug "UserInterrupt, evaluation cancelled"
interpreterLoop :: IO ()
interpreterLoop = do
putMVar evalThreadId =<< myThreadId
-- NOTE: The failure branch of `catch` will `mask` asynchronous exceptions.
let go = forever $ handler `catch` (\UserInterrupt -> return ())
void $ runInterpreter go
return (Hint run cancel, interpreterLoop)