Fix dll-split problem with patch 'Make Core Lint check for locally-bound GlobalId'

The trouble was that my changes made a lot more files transitively link with
DynFlags, which is the root module for the revolting Windows dll-split stuff.

Anyway this patch fixes it, in a good way:

 - Make GHC/Hooks *not* import DsMonad, because DsMonad imports too
   much other stuff (notably tcLookup variants).  Really, Hooks depends
   only on *types* not *code*.

 - To do this I need the DsM type, and the types it depends on,
   not to be part of DsMonad.  So I moved it to TcRnTypes, which is
   where the similar pieces for the TcM and IfM monads live.

 - We can then delete DsMonad.hs-boot

 - There are a bunch of knock-on change, of no great significance

9 files changed, 172 insertions, 210 deletions

diff --git a/compiler/deSugar/DsMeta.hs b/compiler/deSugar/DsMeta.hs
index b236f9cc7b..a94d996e7d 100644
--- a/compiler/deSugar/DsMeta.hs
+++ b/compiler/deSugar/DsMeta.hs
@@ -78,7 +78,7 @@ dsBracket :: HsBracket Name -> [PendingTcSplice] -> DsM CoreExpr
 dsBracket brack splices
   = dsExtendMetaEnv new_bit (do_brack brack)
   where
-    new_bit = mkNameEnv [(n, Splice (unLoc e)) | PendSplice n e <- splices]
+    new_bit = mkNameEnv [(n, DsSplice (unLoc e)) | PendSplice n e <- splices]
 
     do_brack (VarBr _ n) = do { MkC e1  <- lookupOcc n ; return e1 }
     do_brack (ExpBr e)   = do { MkC e1  <- repLE e     ; return e1 }
@@ -970,8 +970,8 @@ repSplice :: HsSplice Name -> DsM (Core a)
 repSplice (HsSplice n _)
  = do { mb_val <- dsLookupMetaEnv n
        ; case mb_val of
-           Just (Splice e) -> do { e' <- dsExpr e
-                                 ; return (MkC e') }
+           Just (DsSplice e) -> do { e' <- dsExpr e
+                                   ; return (MkC e') }
            _ -> pprPanic "HsSplice" (ppr n) }
                         -- Should not happen; statically checked
 
@@ -994,8 +994,8 @@ repE (HsVar x)            =
      ; case mb_val of
         Nothing          -> do { str <- globalVar x
                                ; repVarOrCon x str }
-        Just (Bound y)   -> repVarOrCon x (coreVar y)
-        Just (Splice e)  -> do { e' <- dsExpr e
+        Just (DsBound y)   -> repVarOrCon x (coreVar y)
+        Just (DsSplice e)  -> do { e' <- dsExpr e
                                ; return (MkC e') } }
 repE e@(HsIPVar _) = notHandled "Implicit parameters" (ppr e)
 
@@ -1434,7 +1434,7 @@ addBinds :: [GenSymBind] -> DsM a -> DsM a
 -- Add a list of fresh names for locally bound entities to the
 -- meta environment (which is part of the state carried around
 -- by the desugarer monad)
-addBinds bs m = dsExtendMetaEnv (mkNameEnv [(n,Bound id) | (n,id) <- bs]) m
+addBinds bs m = dsExtendMetaEnv (mkNameEnv [(n,DsBound id) | (n,id) <- bs]) m
 
 dupBinder :: (Name, Name) -> DsM (Name, DsMetaVal)
 dupBinder (new, old)
@@ -1469,9 +1469,9 @@ lookupOcc :: Name -> DsM (Core TH.Name)
 lookupOcc n
   = do {  mb_val <- dsLookupMetaEnv n ;
           case mb_val of
-                Nothing         -> globalVar n
-                Just (Bound x)  -> return (coreVar x)
-                Just (Splice _) -> pprPanic "repE:lookupOcc" (ppr n)
+                Nothing           -> globalVar n
+                Just (DsBound x)  -> return (coreVar x)
+                Just (DsSplice _) -> pprPanic "repE:lookupOcc" (ppr n)
     }
 
 globalVar :: Name -> DsM (Core TH.Name)
diff --git a/compiler/deSugar/DsMonad.hs b/compiler/deSugar/DsMonad.hs
index 7c5619982e..f01a9d8174 100644
--- a/compiler/deSugar/DsMonad.hs
+++ b/compiler/deSugar/DsMonad.hs
@@ -7,6 +7,7 @@
 -}
 
 {-# LANGUAGE FlexibleInstances #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}  -- instance MonadThings is necessarily an orphan
 
 module DsMonad (
         DsM, mapM, mapAndUnzipM,
@@ -64,10 +65,10 @@ import DynFlags
 import ErrUtils
 import FastString
 import Maybes
+import GHC.Fingerprint
 
 import Data.IORef
 import Control.Monad
-import GHC.Fingerprint
 
 {-
 ************************************************************************
@@ -115,17 +116,11 @@ orFail _        _        = CanFail
 {-
 ************************************************************************
 *                                                                      *
-                Monad stuff
+                Monad functions
 *                                                                      *
 ************************************************************************
-
-Now the mondo monad magic (yes, @DsM@ is a silly name)---carry around
-a @UniqueSupply@ and some annotations, which
-presumably include source-file location information:
 -}
 
-type DsM result = TcRnIf DsGblEnv DsLclEnv result
-
 -- Compatibility functions
 fixDs :: (a -> DsM a) -> DsM a
 fixDs    = fixM
@@ -135,62 +130,6 @@ type DsWarning = (SrcSpan, SDoc)
         -- and we'll do the print_unqual stuff later on to turn it
         -- into a Doc.
 
--- If '-XParallelArrays' is given, the desugarer populates this table with the corresponding
--- variables found in 'Data.Array.Parallel'.
---
-data PArrBuiltin
-        = PArrBuiltin
-        { lengthPVar         :: Var     -- ^ lengthP
-        , replicatePVar      :: Var     -- ^ replicateP
-        , singletonPVar      :: Var     -- ^ singletonP
-        , mapPVar            :: Var     -- ^ mapP
-        , filterPVar         :: Var     -- ^ filterP
-        , zipPVar            :: Var     -- ^ zipP
-        , crossMapPVar       :: Var     -- ^ crossMapP
-        , indexPVar          :: Var     -- ^ (!:)
-        , emptyPVar          :: Var     -- ^ emptyP
-        , appPVar            :: Var     -- ^ (+:+)
-        , enumFromToPVar     :: Var     -- ^ enumFromToP
-        , enumFromThenToPVar :: Var     -- ^ enumFromThenToP
-        }
-
-data DsGblEnv
-        = DsGblEnv
-        { ds_mod          :: Module             -- For SCC profiling
-        , ds_fam_inst_env :: FamInstEnv         -- Like tcg_fam_inst_env
-        , ds_unqual  :: PrintUnqualified
-        , ds_msgs    :: IORef Messages          -- Warning messages
-        , ds_if_env  :: (IfGblEnv, IfLclEnv)    -- Used for looking up global,
-                                                -- possibly-imported things
-        , ds_dph_env :: GlobalRdrEnv            -- exported entities of 'Data.Array.Parallel.Prim'
-                                                -- iff '-fvectorise' flag was given as well as
-                                                -- exported entities of 'Data.Array.Parallel' iff
-                                                -- '-XParallelArrays' was given; otherwise, empty
-        , ds_parr_bi :: PArrBuiltin             -- desugarar names for '-XParallelArrays'
-        , ds_static_binds :: IORef [(Fingerprint, (Id,CoreExpr))]
-          -- ^ Bindings resulted from floating static forms
-        }
-
-instance ContainsModule DsGblEnv where
-    extractModule = ds_mod
-
-data DsLclEnv = DsLclEnv {
-        ds_meta    :: DsMetaEnv,        -- Template Haskell bindings
-        ds_loc     :: SrcSpan           -- to put in pattern-matching error msgs
-     }
-
--- Inside [| |] brackets, the desugarer looks
--- up variables in the DsMetaEnv
-type DsMetaEnv = NameEnv DsMetaVal
-
-data DsMetaVal
-   = Bound Id           -- Bound by a pattern inside the [| |].
-                        -- Will be dynamically alpha renamed.
-                        -- The Id has type THSyntax.Var
-
-   | Splice (HsExpr Id) -- These bindings are introduced by
-                        -- the PendingSplices on a HsBracketOut
-
 initDs :: HscEnv
        -> Module -> GlobalRdrEnv -> TypeEnv -> FamInstEnv
        -> DsM a
@@ -302,8 +241,8 @@ mkDsEnvs dflags mod rdr_env type_env fam_inst_env msg_var static_binds_var
                            , ds_parr_bi = panic "DsMonad: uninitialised ds_parr_bi"
                            , ds_static_binds = static_binds_var
                            }
-        lcl_env = DsLclEnv { ds_meta = emptyNameEnv
-                           , ds_loc  = noSrcSpan
+        lcl_env = DsLclEnv { dsl_meta = emptyNameEnv
+                           , dsl_loc  = noSrcSpan
                            }
     in (gbl_env, lcl_env)
 
@@ -366,11 +305,10 @@ getGhcModeDs :: DsM GhcMode
 getGhcModeDs =  getDynFlags >>= return . ghcMode
 
 getSrcSpanDs :: DsM SrcSpan
-getSrcSpanDs = do { env <- getLclEnv; return (ds_loc env) }
+getSrcSpanDs = do { env <- getLclEnv; return (dsl_loc env) }
 
 putSrcSpanDs :: SrcSpan -> DsM a -> DsM a
-putSrcSpanDs new_loc thing_inside = updLclEnv (\ env -> env {ds_loc = new_loc}) thing_inside
-
+putSrcSpanDs new_loc thing_inside = updLclEnv (\ env -> env {dsl_loc = new_loc}) thing_inside
 warnDs :: SDoc -> DsM ()
 warnDs warn = do { env <- getGblEnv
                  ; loc <- getSrcSpanDs
@@ -489,14 +427,14 @@ dsGetFamInstEnvs
        ; return (eps_fam_inst_env eps, ds_fam_inst_env env) }
 
 dsGetMetaEnv :: DsM (NameEnv DsMetaVal)
-dsGetMetaEnv = do { env <- getLclEnv; return (ds_meta env) }
+dsGetMetaEnv = do { env <- getLclEnv; return (dsl_meta env) }
 
 dsLookupMetaEnv :: Name -> DsM (Maybe DsMetaVal)
-dsLookupMetaEnv name = do { env <- getLclEnv; return (lookupNameEnv (ds_meta env) name) }
+dsLookupMetaEnv name = do { env <- getLclEnv; return (lookupNameEnv (dsl_meta env) name) }
 
 dsExtendMetaEnv :: DsMetaEnv -> DsM a -> DsM a
 dsExtendMetaEnv menv thing_inside
-  = updLclEnv (\env -> env { ds_meta = ds_meta env `plusNameEnv` menv }) thing_inside
+  = updLclEnv (\env -> env { dsl_meta = dsl_meta env `plusNameEnv` menv }) thing_inside
 
 -- | Gets a reference to the SPT entries created so far.
 dsGetStaticBindsVar :: DsM (IORef [(Fingerprint, (Id,CoreExpr))])
diff --git a/compiler/deSugar/DsMonad.hs-boot b/compiler/deSugar/DsMonad.hs-boot
deleted file mode 100644
index 12bc5ebcf8..0000000000
--- a/compiler/deSugar/DsMonad.hs-boot
+++ /dev/null
@@ -1,32 +0,0 @@
-module DsMonad (DsM) where
-
-import TcRnTypes
-
-data DsGblEnv
-data DsLclEnv
-type DsM result = TcRnIf DsGblEnv DsLclEnv result
-
-{-
-Some notes about this boot file (from Edsko):
-
-
-DsMonad has a (transitive) dependency on Hooks in at least two ways:
-once through Finder, which imports Packages, which imports Hooks; but
-that's easily solved, because Finder can import PackageState
-instead. However, it is less obvious to me how to resolve the
-following import cycle
-
-- DsMonad imports tcIfaceGlobal from TcIface
-- TcIface imports (loadWiredInHomeIface, loadInterface, loadDecls,
-findAndReadIface) from LoadIface
-- LoadIFace imports Hooks
-
-(There might be still others, this is the most direct one at the moment.)
-
-(Just to be clear, Hooks imports DsMonad because it needs the DsM type
-for the dsForeignsHook.)
-
-I'm sure this cycle can be broken somehow, but I'm not familiar enough
-with this part of the compiler to see if there is a natural point to
-do it.
--}
diff --git a/compiler/ghc.mk b/compiler/ghc.mk
index a33fde8d3f..97e64ecfd0 100644
--- a/compiler/ghc.mk
+++ b/compiler/ghc.mk
@@ -473,12 +473,10 @@ compiler_stage2_dll0_MODULES = \
 	Avail \
 	Bag \
 	BasicTypes \
-	BinIface \
 	Binary \
 	BooleanFormula \
 	BreakArray \
 	BufWrite \
-	BuildTyCl \
 	Class \
 	CmdLineParser \
 	CmmType \
@@ -489,7 +487,6 @@ compiler_stage2_dll0_MODULES = \
 	Constants \
 	CoreArity \
 	CoreFVs \
-	CoreLint \
 	CoreSubst \
 	CoreSyn \
 	CoreTidy \
@@ -501,7 +498,6 @@ compiler_stage2_dll0_MODULES = \
 	Demand \
 	Digraph \
 	DriverPhases \
-	DsMonad \
 	DynFlags \
 	Encoding \
 	ErrUtils \
@@ -512,7 +508,6 @@ compiler_stage2_dll0_MODULES = \
 	FastMutInt \
 	FastString \
 	FastTypes \
-	Finder \
 	Fingerprint \
 	FiniteMap \
 	ForeignCall \
@@ -532,7 +527,6 @@ compiler_stage2_dll0_MODULES = \
 	IOEnv \
 	Id \
 	IdInfo \
-	IfaceEnv \
 	IfaceSyn \
 	IfaceType \
 	InstEnv \
@@ -541,7 +535,6 @@ compiler_stage2_dll0_MODULES = \
 	Lexer \
 	ListSetOps \
 	Literal \
-	LoadIface \
 	Maybes \
 	MkCore \
 	MkId \
@@ -564,7 +557,6 @@ compiler_stage2_dll0_MODULES = \
 	Platform \
 	PlatformConstants \
 	PprCore \
-	PrelInfo \
 	PrelNames \
 	PrelRules \
 	Pretty \
@@ -576,11 +568,8 @@ compiler_stage2_dll0_MODULES = \
 	StaticFlags \
 	StringBuffer \
 	TcEvidence \
-	TcIface \
-	TcRnMonad \
 	TcRnTypes \
 	TcType \
-	TcTypeNats \
 	TrieMap \
 	TyCon \
 	Type \
diff --git a/compiler/main/Hooks.hs b/compiler/main/Hooks.hs
index 44f340aed9..3e797cad2e 100644
--- a/compiler/main/Hooks.hs
+++ b/compiler/main/Hooks.hs
@@ -1,5 +1,10 @@
 -- \section[Hooks]{Low level API hooks}
 
+-- NB: this module is SOURCE-imported by DynFlags, and should primarily
+--     refer to *types*, rather than *code*
+-- If you import too muchhere , then the revolting compiler_stage2_dll0_MODULES
+-- stuff in compiler/ghc.mk makes DynFlags link to too much stuff
+
 module Hooks ( Hooks
              , emptyHooks
              , lookupHook
@@ -27,7 +32,6 @@ import HscTypes
 import HsDecls
 import HsBinds
 import HsExpr
-import {-# SOURCE #-} DsMonad
 import OrdList
 import Id
 import TcRnTypes
diff --git a/compiler/typecheck/TcEnv.hs b/compiler/typecheck/TcEnv.hs
index f9e27fcf90..ca04a71132 100644
--- a/compiler/typecheck/TcEnv.hs
+++ b/compiler/typecheck/TcEnv.hs
@@ -1,7 +1,7 @@
 -- (c) The University of Glasgow 2006
 
 {-# LANGUAGE CPP, FlexibleInstances #-}
-{-# OPTIONS_GHC -fno-warn-orphans #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}  -- instance MonadThings is necessarily an orphan
 
 module TcEnv(
         TyThing(..), TcTyThing(..), TcId,
diff --git a/compiler/typecheck/TcExpr.hs b/compiler/typecheck/TcExpr.hs
index 9a60ffb8ba..f5da0b2014 100644
--- a/compiler/typecheck/TcExpr.hs
+++ b/compiler/typecheck/TcExpr.hs
@@ -36,7 +36,7 @@ import TcPatSyn( tcPatSynBuilderOcc )
 import TcPat
 import TcMType
 import TcType
-import DsMonad hiding (Splice)
+import DsMonad
 import Id
 import ConLike
 import DataCon
diff --git a/compiler/typecheck/TcRnTypes.hs b/compiler/typecheck/TcRnTypes.hs
index 7ea9ae9622..7035bf310d 100644
--- a/compiler/typecheck/TcRnTypes.hs
+++ b/compiler/typecheck/TcRnTypes.hs
@@ -36,6 +36,10 @@ module TcRnTypes(
         TcTypeEnv, TcIdBinder(..), TcTyThing(..), PromotionErr(..),
         pprTcTyThingCategory, pprPECategory,
 
+        -- Desugaring types
+        DsM, DsLclEnv(..), DsGblEnv(..), PArrBuiltin(..),
+        DsMetaEnv, DsMetaVal(..),
+
         -- Template Haskell
         ThStage(..), PendingStuff(..), topStage, topAnnStage, topSpliceStage,
         ThLevel, impLevel, outerLevel, thLevel,
@@ -88,7 +92,7 @@ module TcRnTypes(
         pprArising, pprArisingAt,
 
         -- Misc other types
-        TcId, TcIdSet, TcTyVarBind(..), TcTyVarBinds, HoleSort(..)
+        TcId, TcIdSet, HoleSort(..)
 
   ) where
 
@@ -130,6 +134,7 @@ import DynFlags
 import Outputable
 import ListSetOps
 import FastString
+import GHC.Fingerprint
 
 import Data.Set (Set)
 import Control.Monad (ap, liftM)
@@ -153,27 +158,19 @@ import qualified Language.Haskell.TH as TH
 The monad itself has to be defined here, because it is mentioned by ErrCtxt
 -}
 
--- | Type alias for 'IORef'; the convention is we'll use this for mutable
--- bits of data in 'TcGblEnv' which are updated during typechecking and
--- returned at the end.
-type TcRef a     = IORef a
--- ToDo: when should I refer to it as a 'TcId' instead of an 'Id'?
-type TcId        = Id
-type TcIdSet     = IdSet
-
-
 type TcRnIf a b = IOEnv (Env a b)
-type IfM lcl  = TcRnIf IfGblEnv lcl         -- Iface stuff
-
-type IfG  = IfM ()                          -- Top level
-type IfL  = IfM IfLclEnv                    -- Nested
-
--- | Type-checking and renaming monad: the main monad that most type-checking
--- takes place in.  The global environment is 'TcGblEnv', which tracks
--- all of the top-level type-checking information we've accumulated while
--- checking a module, while the local environment is 'TcLclEnv', which
--- tracks local information as we move inside expressions.
-type TcRn = TcRnIf TcGblEnv TcLclEnv
+type TcRn       = TcRnIf TcGblEnv TcLclEnv    -- Type inference
+type IfM lcl    = TcRnIf IfGblEnv lcl         -- Iface stuff
+type IfG        = IfM ()                      --    Top level
+type IfL        = IfM IfLclEnv                --    Nested
+type DsM        = TcRnIf DsGblEnv DsLclEnv    -- Desugaring
+
+-- TcRn is the type-checking and renaming monad: the main monad that
+-- most type-checking takes place in.  The global environment is
+-- 'TcGblEnv', which tracks all of the top-level type-checking
+-- information we've accumulated while checking a module, while the
+-- local environment is 'TcLclEnv', which tracks local information as
+-- we move inside expressions.
 
 -- | Historical "renaming monad" (now it's just 'TcRn').
 type RnM  = TcRn
@@ -181,26 +178,6 @@ type RnM  = TcRn
 -- | Historical "type-checking monad" (now it's just 'TcRn').
 type TcM  = TcRn
 
-{-
-Representation of type bindings to uninstantiated meta variables used during
-constraint solving.
--}
-
-data TcTyVarBind = TcTyVarBind TcTyVar TcType
-
-type TcTyVarBinds = Bag TcTyVarBind
-
-instance Outputable TcTyVarBind where
-  ppr (TcTyVarBind tv ty) = ppr tv <+> text ":=" <+> ppr ty
-
-{-
-************************************************************************
-*                                                                      *
-                The main environment types
-*                                                                      *
-************************************************************************
--}
-
 -- We 'stack' these envs through the Reader like monad infastructure
 -- as we move into an expression (although the change is focused in
 -- the lcl type).
@@ -226,6 +203,125 @@ instance ContainsDynFlags (Env gbl lcl) where
 instance ContainsModule gbl => ContainsModule (Env gbl lcl) where
     extractModule env = extractModule (env_gbl env)
 
+
+{-
+************************************************************************
+*                                                                      *
+                The interface environments
+              Used when dealing with IfaceDecls
+*                                                                      *
+************************************************************************
+-}
+
+data IfGblEnv
+  = IfGblEnv {
+        -- The type environment for the module being compiled,
+        -- in case the interface refers back to it via a reference that
+        -- was originally a hi-boot file.
+        -- We need the module name so we can test when it's appropriate
+        -- to look in this env.
+        if_rec_types :: Maybe (Module, IfG TypeEnv)
+                -- Allows a read effect, so it can be in a mutable
+                -- variable; c.f. handling the external package type env
+                -- Nothing => interactive stuff, no loops possible
+    }
+
+data IfLclEnv
+  = IfLclEnv {
+        -- The module for the current IfaceDecl
+        -- So if we see   f = \x -> x
+        -- it means M.f = \x -> x, where M is the if_mod
+        if_mod :: Module,
+
+        -- The field is used only for error reporting
+        -- if (say) there's a Lint error in it
+        if_loc :: SDoc,
+                -- Where the interface came from:
+                --      .hi file, or GHCi state, or ext core
+                -- plus which bit is currently being examined
+
+        if_tv_env  :: UniqFM TyVar,     -- Nested tyvar bindings
+                                        -- (and coercions)
+        if_id_env  :: UniqFM Id         -- Nested id binding
+    }
+
+{-
+************************************************************************
+*                                                                      *
+                Desugarer monad
+*                                                                      *
+************************************************************************
+
+Now the mondo monad magic (yes, @DsM@ is a silly name)---carry around
+a @UniqueSupply@ and some annotations, which
+presumably include source-file location information:
+-}
+
+-- If '-XParallelArrays' is given, the desugarer populates this table with the corresponding
+-- variables found in 'Data.Array.Parallel'.
+--
+data PArrBuiltin
+        = PArrBuiltin
+        { lengthPVar         :: Var     -- ^ lengthP
+        , replicatePVar      :: Var     -- ^ replicateP
+        , singletonPVar      :: Var     -- ^ singletonP
+        , mapPVar            :: Var     -- ^ mapP
+        , filterPVar         :: Var     -- ^ filterP
+        , zipPVar            :: Var     -- ^ zipP
+        , crossMapPVar       :: Var     -- ^ crossMapP
+        , indexPVar          :: Var     -- ^ (!:)
+        , emptyPVar          :: Var     -- ^ emptyP
+        , appPVar            :: Var     -- ^ (+:+)
+        , enumFromToPVar     :: Var     -- ^ enumFromToP
+        , enumFromThenToPVar :: Var     -- ^ enumFromThenToP
+        }
+
+data DsGblEnv
+        = DsGblEnv
+        { ds_mod          :: Module             -- For SCC profiling
+        , ds_fam_inst_env :: FamInstEnv         -- Like tcg_fam_inst_env
+        , ds_unqual  :: PrintUnqualified
+        , ds_msgs    :: IORef Messages          -- Warning messages
+        , ds_if_env  :: (IfGblEnv, IfLclEnv)    -- Used for looking up global,
+                                                -- possibly-imported things
+        , ds_dph_env :: GlobalRdrEnv            -- exported entities of 'Data.Array.Parallel.Prim'
+                                                -- iff '-fvectorise' flag was given as well as
+                                                -- exported entities of 'Data.Array.Parallel' iff
+                                                -- '-XParallelArrays' was given; otherwise, empty
+        , ds_parr_bi :: PArrBuiltin             -- desugarar names for '-XParallelArrays'
+        , ds_static_binds :: IORef [(Fingerprint, (Id,CoreExpr))]
+          -- ^ Bindings resulted from floating static forms
+        }
+
+instance ContainsModule DsGblEnv where
+    extractModule = ds_mod
+
+data DsLclEnv = DsLclEnv {
+        dsl_meta    :: DsMetaEnv,        -- Template Haskell bindings
+        dsl_loc     :: SrcSpan           -- to put in pattern-matching error msgs
+     }
+
+-- Inside [| |] brackets, the desugarer looks
+-- up variables in the DsMetaEnv
+type DsMetaEnv = NameEnv DsMetaVal
+
+data DsMetaVal
+   = DsBound Id         -- Bound by a pattern inside the [| |].
+                        -- Will be dynamically alpha renamed.
+                        -- The Id has type THSyntax.Var
+
+   | DsSplice (HsExpr Id) -- These bindings are introduced by
+                          -- the PendingSplices on a HsBracketOut
+
+
+{-
+************************************************************************
+*                                                                      *
+                Global typechecker environment
+*                                                                      *
+************************************************************************
+-}
+
 -- | 'TcGblEnv' describes the top-level of the module at the
 -- point at which the typechecker is finished work.
 -- It is this structure that is handed on to the desugarer
@@ -482,47 +578,6 @@ We gather two sorts of usage information
 
 ************************************************************************
 *                                                                      *
-                The interface environments
-              Used when dealing with IfaceDecls
-*                                                                      *
-************************************************************************
--}
-
-data IfGblEnv
-  = IfGblEnv {
-        -- The type environment for the module being compiled,
-        -- in case the interface refers back to it via a reference that
-        -- was originally a hi-boot file.
-        -- We need the module name so we can test when it's appropriate
-        -- to look in this env.
-        if_rec_types :: Maybe (Module, IfG TypeEnv)
-                -- Allows a read effect, so it can be in a mutable
-                -- variable; c.f. handling the external package type env
-                -- Nothing => interactive stuff, no loops possible
-    }
-
-data IfLclEnv
-  = IfLclEnv {
-        -- The module for the current IfaceDecl
-        -- So if we see   f = \x -> x
-        -- it means M.f = \x -> x, where M is the if_mod
-        if_mod :: Module,
-
-        -- The field is used only for error reporting
-        -- if (say) there's a Lint error in it
-        if_loc :: SDoc,
-                -- Where the interface came from:
-                --      .hi file, or GHCi state, or ext core
-                -- plus which bit is currently being examined
-
-        if_tv_env  :: UniqFM TyVar,     -- Nested tyvar bindings
-                                        -- (and coercions)
-        if_id_env  :: UniqFM Id         -- Nested id binding
-    }
-
-{-
-************************************************************************
-*                                                                      *
                 The local typechecker environment
 *                                                                      *
 ************************************************************************
@@ -619,6 +674,14 @@ pass it inwards.
 
 -}
 
+-- | Type alias for 'IORef'; the convention is we'll use this for mutable
+-- bits of data in 'TcGblEnv' which are updated during typechecking and
+-- returned at the end.
+type TcRef a     = IORef a
+-- ToDo: when should I refer to it as a 'TcId' instead of an 'Id'?
+type TcId        = Id
+type TcIdSet     = IdSet
+
 ---------------------------
 -- Template Haskell stages and levels
 ---------------------------
diff --git a/compiler/typecheck/TcSplice.hs b/compiler/typecheck/TcSplice.hs
index a2ff9777b0..ade40adc1a 100644
--- a/compiler/typecheck/TcSplice.hs
+++ b/compiler/typecheck/TcSplice.hs
@@ -77,7 +77,7 @@ import TcEvidence( TcEvBinds(..) )
 import Id
 import IdInfo
 import DsExpr
-import DsMonad hiding (Splice)
+import DsMonad
 import Serialized
 import ErrUtils
 import SrcLoc