I've re-posted this question to focus more tightly on the specific error, and to better enumerate what I've already tried.
I'm trying to parse some Haskell code during the runtime of a Haskell program using the hint package.
The outer program compiles, but when I run it the inner compilation step fails. I'm getting a description of what I assume is a syntax problem, and a location in the "interactive" code, but I have no idea how to view the code in question.
Here's Main.hs
module Main where
import Data.List (intercalate)
import Polysemy (runM)
import qualified Language.Haskell.Interpreter as H
import qualified Effects as E
handleFailures :: Either H.InterpreterError a -> IO a
handleFailures (Left l) = ioError $ userError $ message l
where
message (H.WontCompile es) = intercalate "\n" (header : map unbox es)
message e = show e
header = "ERROR: Won't compile:"
unbox (H.GhcError e) = e
handleFailures (Right a) = return a
interpretation :: String -> H.Interpreter E.MyEffect
interpretation s = do
H.loadModules ["Effects"]
H.setImportsQ [("Prelude", Nothing), ("Effects", Nothing)]
effect <- H.interpret s (H.as :: E.MyEffect)
return effect
extractProgram :: String -> IO E.MyEffect
extractProgram s = do
p <- H.runInterpreter $ interpretation s
success <- handleFailures p
return success
main :: IO ()
main = do
userProvided <- readFile "UserProvided.hs"
userProgram <- extractProgram userProvided
runM . E.teletypeToIO . E.teletypePlusToIO $ userProgram
Effects.hs defines and provides helpers for a Polysemey Sem monad called MyEffect.
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE LambdaCase, BlockArguments #-}
{-# LANGUAGE GADTs, FlexibleContexts, TypeOperators, DataKinds, PolyKinds, ScopedTypeVariables #-}
module Effects where
import Polysemy
data Teletype m a where
ReadTTY :: Teletype m String
WriteTTY :: String -> Teletype m ()
makeSem ''Teletype
teletypeToIO :: Member (Embed IO) r => Sem (Teletype ': r) a -> Sem r a
teletypeToIO = interpret $ \case
ReadTTY -> embed getLine
WriteTTY msg -> embed $ putStrLn msg
data TeletypePlus m a where
ReadPlus :: TeletypePlus m String
WritePlus :: String -> TeletypePlus m ()
makeSem ''TeletypePlus
teletypePlusToIO :: Member (Embed IO) r => Sem (TeletypePlus ': r) a -> Sem r a
teletypePlusToIO = interpret $ \case
ReadPlus -> embed $ ("+" <>) <$> getLine
WritePlus msg -> embed $ putStrLn $ msg <> "+"
type MyEffect = Sem [TeletypePlus, Teletype, Embed IO] ()
UserProvided.hs contains a simple do expression in MyEffect.
do
i <- readTTY
j <- readPlus
let k = i <> j
writeTTY k
writePlus k
In order to get the polysemy package available at runtime, I have to enter run it from inside a cabal sandbox.
$ cabal build
Build profile: -w ghc-8.8.1 -O1
In order, the following will be built (use -v for more details):
- Hello-Polysemy-0.1.0.0 (exe:Hello-Polysemy) (file Main.hs changed)
Preprocessing executable 'Hello-Polysemy' for Hello-Polysemy-0.1.0.0..
Building executable 'Hello-Polysemy' for Hello-Polysemy-0.1.0.0..
[2 of 2] Compiling Main ( Main.hs, /home/mako/Git/Hello-Polysemy/dist-newstyle/buil/x86_64-linux/ghc-8.8.1/Hello-Polysemy-0.1.0.0/x/Hello-Polysemy/build/Hello-Polysemy/Hello-Polysemy-tmp/Main.o )
Linking /home/mako/Git/Hello-Polysemy/dist-newstyle/build/x86_64-linux/ghc-8.8.1/Hello-Polysemy-0.1.0.0/x/Hello-Polysemy/build/Hello-Polysemy/Hello-Polysemy ...
$ cabal exec bash
... but then ...
$ cabal run
Up to date
Hello-Polysemy: user error (ERROR: Won't compile:
<interactive>:10:135: error:
Operator applied to too few arguments: :)
So far as I can tell the only place I'm using the : operator is in Effects.hs, where (a) I'm actually using the type-operator ':, and (b) compilation succeeds just fine when Effects is imported into Main.hs.
Any suggestions for what the problem might be, or how I could learn more?
I already tried using Language.Haskell.Interpreter.Unsafe.unsafeRunInterpreterWithArgs ["-v4"]. That clarifies that it's talking about ghc-prim:GHC.Types.:{(w) d 66}), but I don't know what to do with that information.
Update:
I've tried various permutations of in-lining the "userProvided" code.
declaring the exact same Effect value inline in Main works fine. Replacing the string read from the file with an inline string of an even simpler value "writePlus \"asdf\"" doesn't change the error message.
