Hi Tom,
There is probably more than one way to do this. Did you try using the
package hint-server? [1] It has a very simple interface: you start a
"server" and obtain a handle; then you can run an interpreter action
using the handle. Something like this:
> runIn handle (interpret msg (as :: MyType))
This expression has type IO (Either InterpreterError MyType). You can
also run an interpreter action in the background.
Keep in mind that the ghc-api is not thread safe, though, so you
should start only one server and put the handle in an MVar....
Hope that helps
Daniel
[1] http://hackage.haskell.org/package/hint-server
On Jun 17, 2010, at 6:35 PM, Tom Jordan wrote:
I'm trying to receive small segments of Haskell code over a socket,
and be able to evaluate them in real time in GHCI.
I've already downloaded Hint and have run the test code, and it's
working great. I'm also using the socket server code from Ch.27 of
"Real World Haskell"
and that is working well also.
directly below is the function from the socket server code that
handles the incoming messages.
Instead of doing this: "putStrLn msg"... I want to send
whatever is captured in "msg" to the GHC interpreter that is used in
the Hint code, something like this: "eval msg".
I'm not sure how to combine both of these functionalities to
get them to work with each other..
-- A simple handler that prints incoming packets
plainHandler :: HandlerFunc
plainHandler addr msg =
putStrLn msg
Below is the full code for the socket server, then below that is
"SomeModule" used in the Hint example test below that.
-- file: ch27/syslogserver.hs
import Data.Bits
import Network.Socket
import Network.BSD
import Data.List
type HandlerFunc = SockAddr -> String -> IO ()
serveLog :: String -- ^ Port number or name; 514 is
default
-> HandlerFunc -- ^ Function to handle incoming
messages
-> IO ()
serveLog port handlerfunc = withSocketsDo $
do -- Look up the port. Either raises an exception or returns
-- a nonempty list.
addrinfos <- getAddrInfo
(Just (defaultHints {addrFlags = [AI_PASSIVE]}))
Nothing (Just port)
let serveraddr = head addrinfos
-- Create a socket
sock <- socket (addrFamily serveraddr) Datagram defaultProtocol
-- Bind it to the address we're listening to
bindSocket sock (addrAddress serveraddr)
-- Loop forever processing incoming data. Ctrl-C to abort.
procMessages sock
where procMessages sock =
do -- Receive one UDP packet, maximum length 1024 bytes,
-- and save its content into msg and its source
-- IP and port into addr
(msg, _, addr) <- recvFrom sock 1024
-- Handle it
handlerfunc addr msg
-- And process more messages
procMessages sock
-- A simple handler that prints incoming packets
plainHandler :: HandlerFunc
plainHandler addr msg =
putStrLn msg
-- main = serveLog "8008" plainHandler
----------------------------------------------------------------------------------------------------------------
module SomeModule(g, h) where
f = head
g = f [f]
h = f
----------------------------------------------------------------------------------------------------------------
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)
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