content: {-
  (c) The AQUA Project, Glasgow University, 1993-1998
  
  \section[CoreMonad]{The core pipeline monad}
  -}
  
  {-# LANGUAGE CPP, UndecidableInstances #-}
  
  module Eta.SimplCore.CoreMonad (
      -- * Configuration of the core-to-core passes
      CoreToDo(..), runWhen, runMaybe,
      SimplifierMode(..),
      FloatOutSwitches(..),
      pprPassDetails,
  
      -- * Plugins
      PluginPass, bindsOnlyPass,
  
      -- * Counting
      SimplCount, doSimplTick, doFreeSimplTick, simplCountN,
      pprSimplCount, plusSimplCount, zeroSimplCount,
      isZeroSimplCount, hasDetailedCounts, Tick(..),
  
      -- * The monad
      CoreM, runCoreM,
  
      -- ** Reading from the monad
      getHscEnv, getRuleBase, getModule,
      getDynFlags, getOrigNameCache, getPackageFamInstEnv,
      getPrintUnqualified,
  
      -- ** Writing to the monad
      addSimplCount,
  
      -- ** Lifting into the monad
      liftIO, liftIOWithCount,
      liftIO1, liftIO2, liftIO3, liftIO4,
  
      -- ** Global initialization
      reinitializeGlobals,
  
      -- ** Dealing with annotations
      getAnnotations, getFirstAnnotations,
  
      -- ** Screen output
      putMsg, putMsgS, errorMsg, errorMsgS,
      fatalErrorMsg, fatalErrorMsgS,
      debugTraceMsg, debugTraceMsgS,
      dumpIfSet_dyn,
  
  #ifdef ETA_REPL
      -- * Getting 'Name's
      thNameToGhcName
  #endif
    ) where
  
  #ifdef ETA_REPL
  import Eta.BasicTypes.Name( Name )
  #endif
  import Eta.Core.CoreSyn
  import Eta.Main.HscTypes
  import Eta.BasicTypes.NameCache
  import Eta.BasicTypes.Module
  import Eta.Main.DynFlags
  import Eta.Main.StaticFlags
  import Eta.Specialise.Rules            ( RuleBase )
  import Eta.BasicTypes.BasicTypes       ( CompilerPhase(..) )
  import Eta.Main.Annotations
  
  import Eta.Utils.IOEnv hiding     ( liftIO, failM, failWithM )
  import qualified Eta.Utils.IOEnv as IOEnv( liftIO )
  import Eta.TypeCheck.TcEnv            ( tcLookupGlobal )
  import Eta.TypeCheck.TcRnMonad        ( initTcForLookup )
  import Eta.BasicTypes.Var
  import Eta.Utils.Outputable
  import qualified Eta.Utils.Outputable as Outputable
  import Eta.Utils.FastString
  import qualified Eta.Main.ErrUtils as Err
  import Eta.Utils.Maybes
  import Eta.BasicTypes.UniqSupply
  import Eta.Utils.UniqFM       ( UniqFM, mapUFM, filterUFM )
  import Eta.Utils.MonadUtils
  
  import Eta.Utils.ListSetOps       ( runs )
  import Data.List
  import Data.Ord
  import Data.Dynamic
  import Data.IORef
  import Data.Map (Map)
  import qualified Data.Map as Map
  import Data.Word
  import qualified Control.Applicative as A
  import Control.Monad
  
  import Prelude hiding   ( read )
  
  #ifdef ETA_REPL
  import {-# SOURCE #-} Eta.TypeCheck.TcSplice ( lookupThName_maybe )
  import qualified Language.Eta.Meta as TH
  
  saveLinkerGlobals :: IO ()
  saveLinkerGlobals = return ()
  
  restoreLinkerGlobals :: () -> IO ()
  restoreLinkerGlobals () = return ()
  #else
  saveLinkerGlobals :: IO ()
  saveLinkerGlobals = return ()
  
  restoreLinkerGlobals :: () -> IO ()
  restoreLinkerGlobals () = return ()
  #endif
  
  
  {-
  ************************************************************************
  *                                                                      *
                The CoreToDo type and related types
            Abstraction of core-to-core passes to run.
  *                                                                      *
  ************************************************************************
  -}
  
  data CoreToDo           -- These are diff core-to-core passes,
                          -- which may be invoked in any order,
                          -- as many times as you like.
  
    = CoreDoSimplify      -- The core-to-core simplifier.
          Int                    -- Max iterations
          SimplifierMode
    | CoreDoPluginPass String PluginPass
    | CoreDoFloatInwards
    | CoreDoFloatOutwards FloatOutSwitches
    | CoreLiberateCase
    | CoreDoPrintCore
    | CoreDoStaticArgs
    | CoreDoCallArity
    | CoreDoStrictness
    | CoreDoWorkerWrapper
    | CoreDoSpecialising
    | CoreDoSpecConstr
    | CoreCSE
    | CoreDoRuleCheck CompilerPhase String   -- Check for non-application of rules
                                             -- matching this string
    | CoreDoVectorisation
    | CoreDoNothing                -- Useful when building up
    | CoreDoPasses [CoreToDo]      -- lists of these things
  
    | CoreDesugar    -- Right after desugaring, no simple optimisation yet!
    | CoreDesugarOpt -- CoreDesugarXXX: Not strictly a core-to-core pass, but produces
                         --                 Core output, and hence useful to pass to endPass
  
    | CoreTidy
    | CorePrep
  
  instance Outputable CoreToDo where
    ppr (CoreDoSimplify _ _)     = ptext (sLit "Simplifier")
    ppr (CoreDoPluginPass s _)   = ptext (sLit "Core plugin: ") <+> text s
    ppr CoreDoFloatInwards       = ptext (sLit "Float inwards")
    ppr (CoreDoFloatOutwards f)  = ptext (sLit "Float out") <> parens (ppr f)
    ppr CoreLiberateCase         = ptext (sLit "Liberate case")
    ppr CoreDoStaticArgs         = ptext (sLit "Static argument")
    ppr CoreDoCallArity          = ptext (sLit "Called arity analysis")
    ppr CoreDoStrictness         = ptext (sLit "Demand analysis")
    ppr CoreDoWorkerWrapper      = ptext (sLit "Worker Wrapper binds")
    ppr CoreDoSpecialising       = ptext (sLit "Specialise")
    ppr CoreDoSpecConstr         = ptext (sLit "SpecConstr")
    ppr CoreCSE                  = ptext (sLit "Common sub-expression")
    ppr CoreDoVectorisation      = ptext (sLit "Vectorisation")
    ppr CoreDesugar              = ptext (sLit "Desugar (before optimization)")
    ppr CoreDesugarOpt           = ptext (sLit "Desugar (after optimization)")
    ppr CoreTidy                 = ptext (sLit "Tidy Core")
    ppr CorePrep                 = ptext (sLit "CorePrep")
    ppr CoreDoPrintCore          = ptext (sLit "Print core")
    ppr (CoreDoRuleCheck {})     = ptext (sLit "Rule check")
    ppr CoreDoNothing            = ptext (sLit "CoreDoNothing")
    ppr (CoreDoPasses {})        = ptext (sLit "CoreDoPasses")
  
  pprPassDetails :: CoreToDo -> SDoc
  pprPassDetails (CoreDoSimplify n md) = vcat [ ptext (sLit "Max iterations =") <+> int n
                                              , ppr md ]
  pprPassDetails _ = Outputable.empty
  
  data SimplifierMode             -- See comments in SimplMonad
    = SimplMode
          { sm_names      :: [String] -- Name(s) of the phase
          , sm_phase      :: CompilerPhase
          , sm_rules      :: Bool     -- Whether RULES are enabled
          , sm_inline     :: Bool     -- Whether inlining is enabled
          , sm_case_case  :: Bool     -- Whether case-of-case is enabled
          , sm_eta_expand :: Bool     -- Whether eta-expansion is enabled
          }
  
  instance Outputable SimplifierMode where
      ppr (SimplMode { sm_phase = p, sm_names = ss
                     , sm_rules = r, sm_inline = i
                     , sm_eta_expand = eta, sm_case_case = cc })
         = ptext (sLit "SimplMode") <+> braces (
           sep [ ptext (sLit "Phase =") <+> ppr p <+>
                 brackets (text (concat $ intersperse "," ss)) <> comma
               , pp_flag i   (sLit "inline") <> comma
               , pp_flag r   (sLit "rules") <> comma
               , pp_flag eta (sLit "eta-expand") <> comma
               , pp_flag cc  (sLit "case-of-case") ])
           where
             pp_flag f s = ppUnless f (ptext (sLit "no")) <+> ptext s
  
  data FloatOutSwitches = FloatOutSwitches {
    floatOutLambdas   :: Maybe Int,  -- ^ Just n <=> float lambdas to top level, if
                                     -- doing so will abstract over n or fewer
                                     -- value variables
                                     -- Nothing <=> float all lambdas to top level,
                                     --             regardless of how many free variables
                                     -- Just 0 is the vanilla case: float a lambda
                                     --    iff it has no free vars
  
    floatOutConstants :: Bool,       -- ^ True <=> float constants to top level,
                                     --            even if they do not escape a lambda
    floatOutOverSatApps :: Bool      -- ^ True <=> float out over-saturated applications
                                     --            based on arity information.
                                     -- See Note [Floating over-saturated applications]
                                     -- in SetLevels
    }
  instance Outputable FloatOutSwitches where
      ppr = pprFloatOutSwitches
  
  pprFloatOutSwitches :: FloatOutSwitches -> SDoc
  pprFloatOutSwitches sw
    = ptext (sLit "FOS") <+> (braces $
       sep $ punctuate comma $
       [ ptext (sLit "Lam =")    <+> ppr (floatOutLambdas sw)
       , ptext (sLit "Consts =") <+> ppr (floatOutConstants sw)
       , ptext (sLit "OverSatApps =")   <+> ppr (floatOutOverSatApps sw) ])
  
  -- The core-to-core pass ordering is derived from the DynFlags:
  runWhen :: Bool -> CoreToDo -> CoreToDo
  runWhen True  do_this = do_this
  runWhen False _       = CoreDoNothing
  
  runMaybe :: Maybe a -> (a -> CoreToDo) -> CoreToDo
  runMaybe (Just x) f = f x
  runMaybe Nothing  _ = CoreDoNothing
  
  {-
  Note [RULEs enabled in SimplGently]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  RULES are enabled when doing "gentle" simplification.  Two reasons:
  
    * We really want the class-op cancellation to happen:
          op (df d1 d2) --> $cop3 d1 d2
      because this breaks the mutual recursion between 'op' and 'df'
  
    * I wanted the RULE
          lift String ===> ...
      to work in Template Haskell when simplifying
      splices, so we get simpler code for literal strings
  
  But watch out: list fusion can prevent floating.  So use phase control
  to switch off those rules until after floating.
  
  
  ************************************************************************
  *                                                                      *
               Types for Plugins
  *                                                                      *
  ************************************************************************
  -}
  
  -- | A description of the plugin pass itself
  type PluginPass = ModGuts -> CoreM ModGuts
  
  bindsOnlyPass :: (CoreProgram -> CoreM CoreProgram) -> ModGuts -> CoreM ModGuts
  bindsOnlyPass pass guts
    = do { binds' <- pass (mg_binds guts)
         ; return (guts { mg_binds = binds' }) }
  
  {-
  ************************************************************************
  *                                                                      *
               Counting and logging
  *                                                                      *
  ************************************************************************
  -}
  
  verboseSimplStats :: Bool
  verboseSimplStats = opt_PprStyle_Debug          -- For now, anyway
  
  zeroSimplCount     :: DynFlags -> SimplCount
  isZeroSimplCount   :: SimplCount -> Bool
  hasDetailedCounts  :: SimplCount -> Bool
  pprSimplCount      :: SimplCount -> SDoc
  doSimplTick        :: DynFlags -> Tick -> SimplCount -> SimplCount
  doFreeSimplTick    ::             Tick -> SimplCount -> SimplCount
  plusSimplCount     :: SimplCount -> SimplCount -> SimplCount
  
  data SimplCount
     = VerySimplCount !Int        -- Used when don't want detailed stats
  
     | SimplCount {
          ticks   :: !Int,        -- Total ticks
          details :: !TickCounts, -- How many of each type
  
          n_log   :: !Int,        -- N
          log1    :: [Tick],      -- Last N events; <= opt_HistorySize,
                                  --   most recent first
          log2    :: [Tick]       -- Last opt_HistorySize events before that
                                  -- Having log1, log2 lets us accumulate the
                                  -- recent history reasonably efficiently
       }
  
  type TickCounts = Map Tick Int
  
  simplCountN :: SimplCount -> Int
  simplCountN (VerySimplCount n)         = n
  simplCountN (SimplCount { ticks = n }) = n
  
  zeroSimplCount dflags
                  -- This is where we decide whether to do
                  -- the VerySimpl version or the full-stats version
    | dopt Opt_D_dump_simpl_stats dflags
    = SimplCount {ticks = 0, details = Map.empty,
                  n_log = 0, log1 = [], log2 = []}
    | otherwise
    = VerySimplCount 0
  
  isZeroSimplCount (VerySimplCount n)         = n==0
  isZeroSimplCount (SimplCount { ticks = n }) = n==0
  
  hasDetailedCounts (VerySimplCount {}) = False
  hasDetailedCounts (SimplCount {})     = True
  
  doFreeSimplTick tick sc@SimplCount { details = dts }
    = sc { details = dts `addTick` tick }
  doFreeSimplTick _ sc = sc
  
  doSimplTick dflags tick
      sc@(SimplCount { ticks = tks, details = dts, n_log = nl, log1 = l1 })
    | nl >= historySize dflags = sc1 { n_log = 1, log1 = [tick], log2 = l1 }
    | otherwise                = sc1 { n_log = nl+1, log1 = tick : l1 }
    where
      sc1 = sc { ticks = tks+1, details = dts `addTick` tick }
  
  doSimplTick _ _ (VerySimplCount n) = VerySimplCount (n+1)
  
  
  -- Don't use Map.unionWith because that's lazy, and we want to
  -- be pretty strict here!
  addTick :: TickCounts -> Tick -> TickCounts
  addTick fm tick = case Map.lookup tick fm of
                          Nothing -> Map.insert tick 1 fm
                          Just n  -> n1 `seq` Map.insert tick n1 fm
                                  where
                                     n1 = n+1
  
  
  plusSimplCount sc1@(SimplCount { ticks = tks1, details = dts1 })
                 sc2@(SimplCount { ticks = tks2, details = dts2 })
    = log_base { ticks = tks1 + tks2, details = Map.unionWith (+) dts1 dts2 }
    where
          -- A hackish way of getting recent log info
      log_base | null (log1 sc2) = sc1    -- Nothing at all in sc2
               | null (log2 sc2) = sc2 { log2 = log1 sc1 }
               | otherwise       = sc2
  
  plusSimplCount (VerySimplCount n) (VerySimplCount m) = VerySimplCount (n+m)
  plusSimplCount _                  _                  = panic "plusSimplCount"
         -- We use one or the other consistently
  
  pprSimplCount (VerySimplCount n) = ptext (sLit "Total ticks:") <+> int n
  pprSimplCount (SimplCount { ticks = tks, details = dts, log1 = l1, log2 = l2 })
    = vcat [ptext (sLit "Total ticks:    ") <+> int tks,
            blankLine,
            pprTickCounts dts,
            if verboseSimplStats then
                  vcat [blankLine,
                        ptext (sLit "Log (most recent first)"),
                        nest 4 (vcat (map ppr l1) $$ vcat (map ppr l2))]
            else Outputable.empty
      ]
  
  pprTickCounts :: Map Tick Int -> SDoc
  pprTickCounts counts
    = vcat (map pprTickGroup groups)
    where
      groups :: [[(Tick,Int)]]    -- Each group shares a comon tag
                                  -- toList returns common tags adjacent
      groups = runs same_tag (Map.toList counts)
      same_tag (tick1,_) (tick2,_) = tickToTag tick1 == tickToTag tick2
  
  pprTickGroup :: [(Tick, Int)] -> SDoc
  pprTickGroup group@((tick1,_):_)
    = hang (int (sum [n | (_,n) <- group]) <+> text (tickString tick1))
         2 (vcat [ int n <+> pprTickCts tick
                                      -- flip as we want largest first
                 | (tick,n) <- sortBy (flip (comparing snd)) group])
  pprTickGroup [] = panic "pprTickGroup"
  
  data Tick
    = PreInlineUnconditionally    Id
    | PostInlineUnconditionally   Id
  
    | UnfoldingDone               Id
    | RuleFired                   FastString      -- Rule name
  
    | LetFloatFromLet
    | EtaExpansion                Id      -- LHS binder
    | EtaReduction                Id      -- Binder on outer lambda
    | BetaReduction               Id      -- Lambda binder
  
  
    | CaseOfCase                  Id      -- Bndr on *inner* case
    | KnownBranch                 Id      -- Case binder
    | CaseMerge                   Id      -- Binder on outer case
    | AltMerge                    Id      -- Case binder
    | CaseElim                    Id      -- Case binder
    | CaseIdentity                Id      -- Case binder
    | FillInCaseDefault           Id      -- Case binder
  
    | BottomFound
    | SimplifierDone              -- Ticked at each iteration of the simplifier
  
  instance Outputable Tick where
    ppr tick = text (tickString tick) <+> pprTickCts tick
  
  instance Eq Tick where
    a == b = case a `cmpTick` b of
             EQ -> True
             _ -> False
  
  instance Ord Tick where
    compare = cmpTick
  
  tickToTag :: Tick -> Int
  tickToTag (PreInlineUnconditionally _)  = 0
  tickToTag (PostInlineUnconditionally _) = 1
  tickToTag (UnfoldingDone _)             = 2
  tickToTag (RuleFired _)                 = 3
  tickToTag LetFloatFromLet               = 4
  tickToTag (EtaExpansion _)              = 5
  tickToTag (EtaReduction _)              = 6
  tickToTag (BetaReduction _)             = 7
  tickToTag (CaseOfCase _)                = 8
  tickToTag (KnownBranch _)               = 9
  tickToTag (CaseMerge _)                 = 10
  tickToTag (CaseElim _)                  = 11
  tickToTag (CaseIdentity _)              = 12
  tickToTag (FillInCaseDefault _)         = 13
  tickToTag BottomFound                   = 14
  tickToTag SimplifierDone                = 16
  tickToTag (AltMerge _)                  = 17
  
  tickString :: Tick -> String
  tickString (PreInlineUnconditionally _) = "PreInlineUnconditionally"
  tickString (PostInlineUnconditionally _)= "PostInlineUnconditionally"
  tickString (UnfoldingDone _)            = "UnfoldingDone"
  tickString (RuleFired _)                = "RuleFired"
  tickString LetFloatFromLet              = "LetFloatFromLet"
  tickString (EtaExpansion _)             = "EtaExpansion"
  tickString (EtaReduction _)             = "EtaReduction"
  tickString (BetaReduction _)            = "BetaReduction"
  tickString (CaseOfCase _)               = "CaseOfCase"
  tickString (KnownBranch _)              = "KnownBranch"
  tickString (CaseMerge _)                = "CaseMerge"
  tickString (AltMerge _)                 = "AltMerge"
  tickString (CaseElim _)                 = "CaseElim"
  tickString (CaseIdentity _)             = "CaseIdentity"
  tickString (FillInCaseDefault _)        = "FillInCaseDefault"
  tickString BottomFound                  = "BottomFound"
  tickString SimplifierDone               = "SimplifierDone"
  
  pprTickCts :: Tick -> SDoc
  pprTickCts (PreInlineUnconditionally v) = ppr v
  pprTickCts (PostInlineUnconditionally v)= ppr v
  pprTickCts (UnfoldingDone v)            = ppr v
  pprTickCts (RuleFired v)                = ppr v
  pprTickCts LetFloatFromLet              = Outputable.empty
  pprTickCts (EtaExpansion v)             = ppr v
  pprTickCts (EtaReduction v)             = ppr v
  pprTickCts (BetaReduction v)            = ppr v
  pprTickCts (CaseOfCase v)               = ppr v
  pprTickCts (KnownBranch v)              = ppr v
  pprTickCts (CaseMerge v)                = ppr v
  pprTickCts (AltMerge v)                 = ppr v
  pprTickCts (CaseElim v)                 = ppr v
  pprTickCts (CaseIdentity v)             = ppr v
  pprTickCts (FillInCaseDefault v)        = ppr v
  pprTickCts _                            = Outputable.empty
  
  cmpTick :: Tick -> Tick -> Ordering
  cmpTick a b = case (tickToTag a `compare` tickToTag b) of
                  GT -> GT
                  EQ -> cmpEqTick a b
                  LT -> LT
  
  cmpEqTick :: Tick -> Tick -> Ordering
  cmpEqTick (PreInlineUnconditionally a)  (PreInlineUnconditionally b)    = a `compare` b
  cmpEqTick (PostInlineUnconditionally a) (PostInlineUnconditionally b)   = a `compare` b
  cmpEqTick (UnfoldingDone a)             (UnfoldingDone b)               = a `compare` b
  cmpEqTick (RuleFired a)                 (RuleFired b)                   = a `compare` b
  cmpEqTick (EtaExpansion a)              (EtaExpansion b)                = a `compare` b
  cmpEqTick (EtaReduction a)              (EtaReduction b)                = a `compare` b
  cmpEqTick (BetaReduction a)             (BetaReduction b)               = a `compare` b
  cmpEqTick (CaseOfCase a)                (CaseOfCase b)                  = a `compare` b
  cmpEqTick (KnownBranch a)               (KnownBranch b)                 = a `compare` b
  cmpEqTick (CaseMerge a)                 (CaseMerge b)                   = a `compare` b
  cmpEqTick (AltMerge a)                  (AltMerge b)                    = a `compare` b
  cmpEqTick (CaseElim a)                  (CaseElim b)                    = a `compare` b
  cmpEqTick (CaseIdentity a)              (CaseIdentity b)                = a `compare` b
  cmpEqTick (FillInCaseDefault a)         (FillInCaseDefault b)           = a `compare` b
  cmpEqTick _                             _                               = EQ
  
  {-
  ************************************************************************
  *                                                                      *
               Monad and carried data structure definitions
  *                                                                      *
  ************************************************************************
  -}
  
  newtype CoreState = CoreState {
          cs_uniq_supply :: UniqSupply
  }
  
  data CoreReader = CoreReader {
          cr_hsc_env :: HscEnv,
          cr_rule_base :: RuleBase,
          cr_module :: Module,
          cr_print_unqual :: PrintUnqualified,
  #ifdef ETA_REPL
          cr_globals :: ()
  #endif
  }
  
  -- Note: CoreWriter used to be defined with data, rather than newtype.  If it
  -- is defined that way again, the cw_simpl_count field, at least, must be
  -- strict to avoid a space leak (Trac #7702).
  newtype CoreWriter = CoreWriter {
          cw_simpl_count :: SimplCount
  }
  
  emptyWriter :: DynFlags -> CoreWriter
  emptyWriter dflags = CoreWriter {
          cw_simpl_count = zeroSimplCount dflags
      }
  
  plusWriter :: CoreWriter -> CoreWriter -> CoreWriter
  plusWriter w1 w2 = CoreWriter {
          cw_simpl_count = (cw_simpl_count w1) `plusSimplCount` (cw_simpl_count w2)
      }
  
  type CoreIOEnv = IOEnv CoreReader
  
  -- | The monad used by Core-to-Core passes to access common state, register simplification
  -- statistics and so on
  newtype CoreM a = CoreM { unCoreM :: CoreState -> CoreIOEnv (a, CoreState, CoreWriter) }
  
  instance Functor CoreM where
      fmap f ma = do
          a <- ma
          return (f a)
  
  instance Monad CoreM where
      return x = CoreM (\s -> nop s x)
      mx >>= f = CoreM $ \s -> do
              (x, s', w1) <- unCoreM mx s
              (y, s'', w2) <- unCoreM (f x) s'
              let w = w1 `plusWriter` w2
              return $ seq w (y, s'', w)
              -- forcing w before building the tuple avoids a space leak
              -- (Trac #7702)
  instance A.Applicative CoreM where
      pure = return
      (<*>) = ap
      (*>) = (>>)
  
  #if __GLASGOW_HASKELL__ > 800
  instance A.Alternative CoreM where
      empty   = CoreM (const A.empty)
      m <|> n = CoreM (\rs -> unCoreM m rs A.<|> unCoreM n rs)
  
  instance MonadPlus CoreM
  #else
  instance MonadPlus IO => A.Alternative CoreM where
      empty = mzero
      (<|>) = mplus
  
  -- For use if the user has imported Control.Monad.Error from MTL
  -- Requires UndecidableInstances
  instance MonadPlus IO => MonadPlus CoreM where
      mzero = CoreM (const mzero)
      m `mplus` n = CoreM (\rs -> unCoreM m rs `mplus` unCoreM n rs)
  #endif
  
  
  instance MonadUnique CoreM where
      getUniqueSupplyM = do
          us <- getS cs_uniq_supply
          let (us1, us2) = splitUniqSupply us
          modifyS (\s -> s { cs_uniq_supply = us2 })
          return us1
  
      getUniqueM = do
          us <- getS cs_uniq_supply
          let (u,us') = takeUniqFromSupply us
          modifyS (\s -> s { cs_uniq_supply = us' })
          return u
  
  runCoreM :: HscEnv
           -> RuleBase
           -> UniqSupply
           -> Module
           -> PrintUnqualified
           -> CoreM a
           -> IO (a, SimplCount)
  runCoreM hsc_env rule_base us mod print_unqual m = do
          glbls <- saveLinkerGlobals
          liftM extract $ runIOEnv (reader glbls) $ unCoreM m state
    where
      reader glbls = CoreReader {
              cr_hsc_env = hsc_env,
              cr_rule_base = rule_base,
              cr_module = mod,
              cr_globals = glbls,
              cr_print_unqual = print_unqual
          }
      state = CoreState {
              cs_uniq_supply = us
          }
  
      extract :: (a, CoreState, CoreWriter) -> (a, SimplCount)
      extract (value, _, writer) = (value, cw_simpl_count writer)
  
  {-
  ************************************************************************
  *                                                                      *
               Core combinators, not exported
  *                                                                      *
  ************************************************************************
  -}
  
  nop :: CoreState -> a -> CoreIOEnv (a, CoreState, CoreWriter)
  nop s x = do
      r <- getEnv
      return (x, s, emptyWriter $ (hsc_dflags . cr_hsc_env) r)
  
  read :: (CoreReader -> a) -> CoreM a
  read f = CoreM (\s -> getEnv >>= (\r -> nop s (f r)))
  
  getS :: (CoreState -> a) -> CoreM a
  getS f = CoreM (\s -> nop s (f s))
  
  modifyS :: (CoreState -> CoreState) -> CoreM ()
  modifyS f = CoreM (\s -> nop (f s) ())
  
  write :: CoreWriter -> CoreM ()
  write w = CoreM (\s -> return ((), s, w))
  
  -- \subsection{Lifting IO into the monad}
  
  -- | Lift an 'IOEnv' operation into 'CoreM'
  liftIOEnv :: CoreIOEnv a -> CoreM a
  liftIOEnv mx = CoreM (\s -> mx >>= (\x -> nop s x))
  
  instance MonadIO CoreM where
      liftIO = liftIOEnv . IOEnv.liftIO
  
  -- | Lift an 'IO' operation into 'CoreM' while consuming its 'SimplCount'
  liftIOWithCount :: IO (SimplCount, a) -> CoreM a
  liftIOWithCount what = liftIO what >>= (\(count, x) -> addSimplCount count >> return x)
  
  {-
  ************************************************************************
  *                                                                      *
               Reader, writer and state accessors
  *                                                                      *
  ************************************************************************
  -}
  
  getHscEnv :: CoreM HscEnv
  getHscEnv = read cr_hsc_env
  
  getRuleBase :: CoreM RuleBase
  getRuleBase = read cr_rule_base
  
  getPrintUnqualified :: CoreM PrintUnqualified
  getPrintUnqualified = read cr_print_unqual
  
  addSimplCount :: SimplCount -> CoreM ()
  addSimplCount count = write (CoreWriter { cw_simpl_count = count })
  
  -- Convenience accessors for useful fields of HscEnv
  
  instance HasDynFlags CoreM where
      getDynFlags = fmap hsc_dflags getHscEnv
  
  instance HasModule CoreM where
      getModule = read cr_module
  
  -- | The original name cache is the current mapping from 'Module' and
  -- 'OccName' to a compiler-wide unique 'Name'
  getOrigNameCache :: CoreM OrigNameCache
  getOrigNameCache = do
      nameCacheRef <- fmap hsc_NC getHscEnv
      liftIO $ fmap nsNames $ readIORef nameCacheRef
  
  getPackageFamInstEnv :: CoreM PackageFamInstEnv
  getPackageFamInstEnv = do
      hsc_env <- getHscEnv
      eps <- liftIO $ hscEPS hsc_env
      return $ eps_fam_inst_env eps
  
  {-
  ************************************************************************
  *                                                                      *
               Initializing globals
  *                                                                      *
  ************************************************************************
  
  This is a rather annoying function. When a plugin is loaded, it currently
  gets linked against a *newly loaded* copy of the GHC package. This would
  not be a problem, except that the new copy has its own mutable state
  that is not shared with that state that has already been initialized by
  the original GHC package.
  
  (NB This mechanism is sufficient for granting plugins read-only access to
  globals that are guaranteed to be initialized before the plugin is loaded.  If
  any further synchronization is necessary, I would suggest using the more
  sophisticated mechanism involving GHC.Conc.Sync.sharedCAF and rts/Globals.c to
  share a single instance of the global variable among the compiler and the
  plugins.  Perhaps we should migrate all global variables to use that mechanism,
  for robustness... -- NSF July 2013)
  
  This leads to loaded plugins calling GHC code which pokes the static flags,
  and then dying with a panic because the static flags *it* sees are uninitialized.
  
  There are two possible solutions:
    1. Export the symbols from the GHC executable from the GHC library and link
       against this existing copy rather than a new copy of the GHC library
    2. Carefully ensure that the global state in the two copies of the GHC
       library matches
  
  I tried 1. and it *almost* works (and speeds up plugin load times!) except
  on Windows. On Windows the GHC library tends to export more than 65536 symbols
  (see #5292) which overflows the limit of what we can export from the EXE and
  causes breakage.
  
  (Note that if the GHC executable was dynamically linked this wouldn't be a
  problem, because we could share the GHC library it links to.)
  
  We are going to try 2. instead. Unfortunately, this means that every plugin
  will have to say `reinitializeGlobals` before it does anything, but never mind.
  
  I've threaded the cr_globals through CoreM rather than giving them as an
  argument to the plugin function so that we can turn this function into
  (return ()) without breaking any plugins when we eventually get 1. working.
  -}
  
  reinitializeGlobals :: CoreM ()
  reinitializeGlobals = do
      linker_globals <- read cr_globals
      hsc_env <- getHscEnv
      let dflags = hsc_dflags hsc_env
      liftIO $ restoreLinkerGlobals linker_globals
      liftIO $ setUnsafeGlobalDynFlags dflags
  
  {-
  ************************************************************************
  *                                                                      *
               Dealing with annotations
  *                                                                      *
  ************************************************************************
  -}
  
  -- | Get all annotations of a given type. This happens lazily, that is
  -- no deserialization will take place until the [a] is actually demanded and
  -- the [a] can also be empty (the UniqFM is not filtered).
  --
  -- This should be done once at the start of a Core-to-Core pass that uses
  -- annotations.
  --
  -- See Note [Annotations]
  getAnnotations :: Typeable a => ([Word8] -> a) -> ModGuts -> CoreM (UniqFM [a])
  getAnnotations deserialize guts = do
       hsc_env <- getHscEnv
       ann_env <- liftIO $ prepareAnnotations hsc_env (Just guts)
       return (deserializeAnns deserialize ann_env)
  
  -- | Get at most one annotation of a given type per Unique.
  getFirstAnnotations :: Typeable a => ([Word8] -> a) -> ModGuts -> CoreM (UniqFM a)
  getFirstAnnotations deserialize guts
    = liftM (mapUFM head . filterUFM (not . null))
    $ getAnnotations deserialize guts
  
  {-
  Note [Annotations]
  ~~~~~~~~~~~~~~~~~~
  A Core-to-Core pass that wants to make use of annotations calls
  getAnnotations or getFirstAnnotations at the beginning to obtain a UniqFM with
  annotations of a specific type. This produces all annotations from interface
  files read so far. However, annotations from interface files read during the
  pass will not be visible until getAnnotations is called again. This is similar
  to how rules work and probably isn't too bad.
  
  The current implementation could be optimised a bit: when looking up
  annotations for a thing from the HomePackageTable, we could search directly in
  the module where the thing is defined rather than building one UniqFM which
  contains all annotations we know of. This would work because annotations can
  only be given to things defined in the same module. However, since we would
  only want to deserialise every annotation once, we would have to build a cache
  for every module in the HTP. In the end, it's probably not worth it as long as
  we aren't using annotations heavily.
  
  ************************************************************************
  *                                                                      *
                  Direct screen output
  *                                                                      *
  ************************************************************************
  -}
  
  msg :: (DynFlags -> SDoc -> IO ()) -> SDoc -> CoreM ()
  msg how doc = do
          dflags <- getDynFlags
          liftIO $ how dflags doc
  
  -- | Output a String message to the screen
  putMsgS :: String -> CoreM ()
  putMsgS = putMsg . text
  
  -- | Output a message to the screen
  putMsg :: SDoc -> CoreM ()
  putMsg = msg Err.putMsg
  
  -- | Output a string error to the screen
  errorMsgS :: String -> CoreM ()
  errorMsgS = errorMsg . text
  
  -- | Output an error to the screen
  errorMsg :: SDoc -> CoreM ()
  errorMsg = msg Err.errorMsg
  
  -- | Output a fatal string error to the screen. Note this does not by itself cause the compiler to die
  fatalErrorMsgS :: String -> CoreM ()
  fatalErrorMsgS = fatalErrorMsg . text
  
  -- | Output a fatal error to the screen. Note this does not by itself cause the compiler to die
  fatalErrorMsg :: SDoc -> CoreM ()
  fatalErrorMsg = msg Err.fatalErrorMsg
  
  -- | Output a string debugging message at verbosity level of @-v@ or higher
  debugTraceMsgS :: String -> CoreM ()
  debugTraceMsgS = debugTraceMsg . text
  
  -- | Outputs a debugging message at verbosity level of @-v@ or higher
  debugTraceMsg :: SDoc -> CoreM ()
  debugTraceMsg = msg (flip Err.debugTraceMsg 3)
  
  -- | Show some labelled 'SDoc' if a particular flag is set or at a verbosity level of @-v -ddump-most@ or higher
  dumpIfSet_dyn :: DumpFlag -> String -> SDoc -> CoreM ()
  dumpIfSet_dyn flag str = msg (\dflags -> Err.dumpIfSet_dyn dflags flag str)
  
  {-
  ************************************************************************
  *                                                                      *
                 Finding TyThings
  *                                                                      *
  ************************************************************************
  -}
  
  instance MonadThings CoreM where
      lookupThing name = do
          hsc_env <- getHscEnv
          liftIO $ initTcForLookup hsc_env (tcLookupGlobal name)
  
  {-
  ************************************************************************
  *                                                                      *
                 Template Haskell interoperability
  *                                                                      *
  ************************************************************************
  -}
  
  #ifdef ETA_REPL
  -- | Attempt to convert a Template Haskell name to one that GHC can
  -- understand. Original TH names such as those you get when you use
  -- the @'foo@ syntax will be translated to their equivalent GHC name
  -- exactly. Qualified or unqualifed TH names will be dynamically bound
  -- to names in the module being compiled, if possible. Exact TH names
  -- will be bound to the name they represent, exactly.
  thNameToGhcName :: TH.Name -> CoreM (Maybe Name)
  thNameToGhcName th_name = do
      hsc_env <- getHscEnv
      liftIO $ initTcForLookup hsc_env (lookupThName_maybe th_name)
  #endif
  