GHC.Driver.Monad

Ghc monad stuff

class (Functor m, ExceptionMonad m, HasDynFlags m, HasLogger m) => GhcMonad m where

A monad that has all the features needed by GHC API calls.

In short, a GHC monad

• allows embedding of IO actions,
• can log warnings,
• allows handling of (extensible) exceptions, and
• maintains a current session.

If you do not use Ghc or GhcT, make sure to call initGhcMonad before any call to the GHC API functions can occur.

Methods

getSession :: m HscEnv

setSession :: HscEnv -> m ()

Instances

GhcMonad Ghc

Defined in GHC.Driver.Monad

Methods

getSession :: Ghc HscEnv

setSession :: HscEnv -> Ghc ()

ExceptionMonad m => GhcMonad (GhcT m)

Defined in GHC.Driver.Monad

Methods

getSession :: GhcT m HscEnv

setSession :: HscEnv -> GhcT m ()

newtype Ghc a

A minimal implementation of a GhcMonad. If you need a custom monad, e.g., to maintain additional state consider wrapping this monad or using GhcT.

Constructors

Ghc

Fields

• unGhc :: Session -> IO a

Instances

MonadFix Ghc

Defined in GHC.Driver.Monad

Methods

mfix :: (a -> Ghc a) -> Ghc a

MonadIO Ghc

Defined in GHC.Driver.Monad

Methods

liftIO :: IO a -> Ghc a

Applicative Ghc

Defined in GHC.Driver.Monad

Methods

pure :: a -> Ghc a

(<*>) :: Ghc (a -> b) -> Ghc a -> Ghc b

liftA2 :: (a -> b -> c) -> Ghc a -> Ghc b -> Ghc c

(*>) :: Ghc a -> Ghc b -> Ghc b

(<*) :: Ghc a -> Ghc b -> Ghc a

Functor Ghc

Defined in GHC.Driver.Monad

Methods

fmap :: (a -> b) -> Ghc a -> Ghc b

(<$) :: a -> Ghc b -> Ghc a

Monad Ghc

Defined in GHC.Driver.Monad

Methods

(>>=) :: Ghc a -> (a -> Ghc b) -> Ghc b

(>>) :: Ghc a -> Ghc b -> Ghc b

return :: a -> Ghc a

MonadCatch Ghc

Defined in GHC.Driver.Monad

Methods

catch :: Exception e => Ghc a -> (e -> Ghc a) -> Ghc a

MonadMask Ghc

Defined in GHC.Driver.Monad

Methods

mask :: ((forall a. Ghc a -> Ghc a) -> Ghc b) -> Ghc b

uninterruptibleMask :: ((forall a. Ghc a -> Ghc a) -> Ghc b) -> Ghc b

generalBracket :: Ghc a -> (a -> ExitCase b -> Ghc c) -> (a -> Ghc b) -> Ghc (b, c)

MonadThrow Ghc

Defined in GHC.Driver.Monad

Methods

throwM :: Exception e => e -> Ghc a

GhcMonad Ghc

Defined in GHC.Driver.Monad

Methods

getSession :: Ghc HscEnv

setSession :: HscEnv -> Ghc ()

HasDynFlags Ghc

Defined in GHC.Driver.Monad

Methods

getDynFlags :: Ghc DynFlags

HasLogger Ghc

Defined in GHC.Driver.Monad

Methods

getLogger :: Ghc Logger

newtype GhcT m a

A monad transformer to add GHC specific features to another monad.

Note that the wrapped monad must support IO and handling of exceptions.

Constructors

GhcT

Fields

• unGhcT :: Session -> m a

Instances

MonadIO m => MonadIO (GhcT m)

Defined in GHC.Driver.Monad

Methods

liftIO :: IO a -> GhcT m a

Applicative m => Applicative (GhcT m)

Defined in GHC.Driver.Monad

Methods

pure :: a -> GhcT m a

(<*>) :: GhcT m (a -> b) -> GhcT m a -> GhcT m b

liftA2 :: (a -> b -> c) -> GhcT m a -> GhcT m b -> GhcT m c

(*>) :: GhcT m a -> GhcT m b -> GhcT m b

(<*) :: GhcT m a -> GhcT m b -> GhcT m a

Functor m => Functor (GhcT m)

Defined in GHC.Driver.Monad

Methods

fmap :: (a -> b) -> GhcT m a -> GhcT m b

(<$) :: a -> GhcT m b -> GhcT m a

Monad m => Monad (GhcT m)

Defined in GHC.Driver.Monad

Methods

(>>=) :: GhcT m a -> (a -> GhcT m b) -> GhcT m b

(>>) :: GhcT m a -> GhcT m b -> GhcT m b

return :: a -> GhcT m a

MonadCatch m => MonadCatch (GhcT m)

Defined in GHC.Driver.Monad

Methods

catch :: Exception e => GhcT m a -> (e -> GhcT m a) -> GhcT m a

MonadMask m => MonadMask (GhcT m)

Defined in GHC.Driver.Monad

Methods

mask :: ((forall a. GhcT m a -> GhcT m a) -> GhcT m b) -> GhcT m b

uninterruptibleMask :: ((forall a. GhcT m a -> GhcT m a) -> GhcT m b) -> GhcT m b

generalBracket :: GhcT m a -> (a -> ExitCase b -> GhcT m c) -> (a -> GhcT m b) -> GhcT m (b, c)

MonadThrow m => MonadThrow (GhcT m)

Defined in GHC.Driver.Monad

Methods

throwM :: Exception e => e -> GhcT m a

ExceptionMonad m => GhcMonad (GhcT m)

Defined in GHC.Driver.Monad

Methods

getSession :: GhcT m HscEnv

setSession :: HscEnv -> GhcT m ()

MonadIO m => HasDynFlags (GhcT m)

Defined in GHC.Driver.Monad

Methods

getDynFlags :: GhcT m DynFlags

MonadIO m => HasLogger (GhcT m)

Defined in GHC.Driver.Monad

Methods

getLogger :: GhcT m Logger

liftGhcT :: m a -> GhcT m a

reflectGhc :: Ghc a -> Session -> IO a

Reflect a computation in the Ghc monad into the IO monad.

You can use this to call functions returning an action in the Ghc monad inside an IO action. This is needed for some (too restrictive) callback arguments of some library functions:

libFunc :: String -> (Int -> IO a) -> IO a
ghcFunc :: Int -> Ghc a

ghcFuncUsingLibFunc :: String -> Ghc a -> Ghc a
ghcFuncUsingLibFunc str =
  reifyGhc $ \s ->
    libFunc $ \i -> do
      reflectGhc (ghcFunc i) s

reifyGhc :: (Session -> IO a) -> Ghc a

getSessionDynFlags :: GhcMonad m => m DynFlags

Grabs the DynFlags from the Session

liftIO :: MonadIO m => IO a -> m a

Lift a computation from the IO monad. This allows us to run IO computations in any monadic stack, so long as it supports these kinds of operations (i.e. IO is the base monad for the stack).

Example

import Control.Monad.Trans.State -- from the "transformers" library

printState :: Show s => StateT s IO ()
printState = do
  state <- get
  liftIO $ print state

Had we omitted liftIO, we would have ended up with this error:

• Couldn't match type ‘IO’ with ‘StateT s IO’
 Expected type: StateT s IO ()
   Actual type: IO ()

The important part here is the mismatch between StateT s IO () and IO ().

Luckily, we know of a function that takes an IO a and returns an (m a): liftIO, enabling us to run the program and see the expected results:

> evalStateT printState "hello"
"hello"

> evalStateT printState 3
3

data Session

The Session is a handle to the complete state of a compilation session. A compilation session consists of a set of modules constituting the current program or library, the context for interactive evaluation, and various caches.

Constructors

Session !(IORef HscEnv)

withSession :: GhcMonad m => (HscEnv -> m a) -> m a

Call the argument with the current session.

modifySession :: GhcMonad m => (HscEnv -> HscEnv) -> m ()

Set the current session to the result of applying the current session to the argument.

modifySessionM :: GhcMonad m => (HscEnv -> m HscEnv) -> m ()

Set the current session to the result of applying the current session to the argument.

withTempSession :: GhcMonad m => (HscEnv -> HscEnv) -> m a -> m a

Call an action with a temporarily modified Session.

Logger

modifyLogger :: GhcMonad m => (Logger -> Logger) -> m ()

Modify the logger

pushLogHookM :: GhcMonad m => (LogAction -> LogAction) -> m ()

Push a log hook on the stack

popLogHookM :: GhcMonad m => m ()

Pop a log hook from the stack

putLogMsgM :: GhcMonad m => MessageClass -> SrcSpan -> SDoc -> m ()

Put a log message

putMsgM :: GhcMonad m => SDoc -> m ()

Put a log message

withTimingM :: GhcMonad m => SDoc -> (b -> ()) -> m b -> m b

Time an action

Diagnostics

logDiagnostics :: GhcMonad m => Messages GhcMessage -> m ()

A monad that allows logging of diagnostics.

printException :: (HasLogger m, MonadIO m, HasDynFlags m) => SourceError -> m ()

Print the all diagnostics in a SourceError. Useful inside exception handlers.

type WarnErrLogger = forall m. (HasDynFlags m, MonadIO m, HasLogger m) => Maybe SourceError -> m ()

A function called to log warnings and errors.

defaultWarnErrLogger :: WarnErrLogger