Enhance UnitId use

* use UnitId instead of String to identify wired-in units
* use UnitId instead of Unit in the backend (Unit are only use by
  Backpack to produce type-checked interfaces, not real code)
* rename lookup functions for consistency
* documentation

28 files changed, 152 insertions, 129 deletions

diff --git a/compiler/GHC/Builtin/Names.hs b/compiler/GHC/Builtin/Names.hs
index 36aba77356..a3d1fa5d5b 100644
--- a/compiler/GHC/Builtin/Names.hs
+++ b/compiler/GHC/Builtin/Names.hs
@@ -614,7 +614,7 @@ rOOT_MAIN       = mkMainModule (fsLit ":Main") -- Root module for initialisation
 
 mkInteractiveModule :: Int -> Module
 -- (mkInteractiveMoudule 9) makes module 'interactive:M9'
-mkInteractiveModule n = mkModule interactiveUnitId (mkModuleName ("Ghci" ++ show n))
+mkInteractiveModule n = mkModule interactiveUnit (mkModuleName ("Ghci" ++ show n))
 
 pRELUDE_NAME, mAIN_NAME :: ModuleName
 pRELUDE_NAME   = mkModuleNameFS (fsLit "Prelude")
@@ -625,28 +625,28 @@ dATA_ARRAY_PARALLEL_NAME      = mkModuleNameFS (fsLit "Data.Array.Parallel")
 dATA_ARRAY_PARALLEL_PRIM_NAME = mkModuleNameFS (fsLit "Data.Array.Parallel.Prim")
 
 mkPrimModule :: FastString -> Module
-mkPrimModule m = mkModule primUnitId (mkModuleNameFS m)
+mkPrimModule m = mkModule primUnit (mkModuleNameFS m)
 
 mkIntegerModule :: FastString -> Module
-mkIntegerModule m = mkModule integerUnitId (mkModuleNameFS m)
+mkIntegerModule m = mkModule integerUnit (mkModuleNameFS m)
 
 mkBaseModule :: FastString -> Module
-mkBaseModule m = mkModule baseUnitId (mkModuleNameFS m)
+mkBaseModule m = mkBaseModule_ (mkModuleNameFS m)
 
 mkBaseModule_ :: ModuleName -> Module
-mkBaseModule_ m = mkModule baseUnitId m
+mkBaseModule_ m = mkModule baseUnit m
 
 mkThisGhcModule :: FastString -> Module
-mkThisGhcModule m = mkModule thisGhcUnitId (mkModuleNameFS m)
+mkThisGhcModule m = mkThisGhcModule_ (mkModuleNameFS m)
 
 mkThisGhcModule_ :: ModuleName -> Module
-mkThisGhcModule_ m = mkModule thisGhcUnitId m
+mkThisGhcModule_ m = mkModule thisGhcUnit m
 
 mkMainModule :: FastString -> Module
-mkMainModule m = mkModule mainUnitId (mkModuleNameFS m)
+mkMainModule m = mkModule mainUnit (mkModuleNameFS m)
 
 mkMainModule_ :: ModuleName -> Module
-mkMainModule_ m = mkModule mainUnitId m
+mkMainModule_ m = mkModule mainUnit m
 
 {-
 ************************************************************************
diff --git a/compiler/GHC/Builtin/Names/TH.hs b/compiler/GHC/Builtin/Names/TH.hs
index 3cd55b566d..4dd1b43e83 100644
--- a/compiler/GHC/Builtin/Names/TH.hs
+++ b/compiler/GHC/Builtin/Names/TH.hs
@@ -170,7 +170,7 @@ thLib = mkTHModule (fsLit "Language.Haskell.TH.Lib.Internal")
 qqLib = mkTHModule (fsLit "Language.Haskell.TH.Quote")
 
 mkTHModule :: FastString -> Module
-mkTHModule m = mkModule thUnitId (mkModuleNameFS m)
+mkTHModule m = mkModule thUnit (mkModuleNameFS m)
 
 libFun, libTc, thFun, thTc, thCls, thCon, qqFun :: FastString -> Unique -> Name
 libFun = mk_known_key_name varName  thLib
diff --git a/compiler/GHC/ByteCode/Linker.hs b/compiler/GHC/ByteCode/Linker.hs
index 1fab779619..03c03fbf2b 100644
--- a/compiler/GHC/ByteCode/Linker.hs
+++ b/compiler/GHC/ByteCode/Linker.hs
@@ -169,7 +169,7 @@ nameToCLabel n suffix = mkFastString label
     occPart     = encodeZ (occNameFS (nameOccName n))
 
     label = concat
-        [ if pkgKey == mainUnitId then "" else packagePart ++ "_"
+        [ if pkgKey == mainUnit then "" else packagePart ++ "_"
         , modulePart
         , '_':occPart
         , '_':suffix
diff --git a/compiler/GHC/Cmm/CLabel.hs b/compiler/GHC/Cmm/CLabel.hs
index 8d85c5aed0..a0f8c6340d 100644
--- a/compiler/GHC/Cmm/CLabel.hs
+++ b/compiler/GHC/Cmm/CLabel.hs
@@ -186,7 +186,7 @@ data CLabel
 
   -- | A label from a .cmm file that is not associated with a .hs level Id.
   | CmmLabel
-        Unit                    -- what package the label belongs to.
+        UnitId                  -- what package the label belongs to.
         FastString              -- identifier giving the prefix of the label
         CmmLabelInfo            -- encodes the suffix of the label
 
@@ -552,7 +552,7 @@ mkSRTInfoLabel n = CmmLabel rtsUnitId lbl CmmInfo
 -----
 mkCmmInfoLabel,   mkCmmEntryLabel, mkCmmRetInfoLabel, mkCmmRetLabel,
   mkCmmCodeLabel, mkCmmDataLabel,  mkCmmClosureLabel
-        :: Unit -> FastString -> CLabel
+        :: UnitId -> FastString -> CLabel
 
 mkCmmInfoLabel      pkg str     = CmmLabel pkg str CmmInfo
 mkCmmEntryLabel     pkg str     = CmmLabel pkg str CmmEntry
@@ -583,7 +583,7 @@ mkApEntryLabel       upd off    = RtsLabel (RtsApEntry           upd off)
 -- A call to some primitive hand written Cmm code
 mkPrimCallLabel :: PrimCall -> CLabel
 mkPrimCallLabel (PrimCall str pkg)
-        = CmmLabel pkg str CmmPrimCall
+        = CmmLabel (toUnitId pkg) str CmmPrimCall
 
 
 -- Constructing ForeignLabels
@@ -1032,7 +1032,7 @@ labelDynamic config this_mod lbl =
   case lbl of
    -- is the RTS in a DLL or not?
    RtsLabel _ ->
-     externalDynamicRefs && (this_pkg /= rtsUnitId)
+     externalDynamicRefs && (this_pkg /= rtsUnit)
 
    IdLabel n _ _ ->
      externalDynamicRefs && isDynLinkName platform this_mod n
@@ -1040,7 +1040,7 @@ labelDynamic config this_mod lbl =
    -- When compiling in the "dyn" way, each package is to be linked into
    -- its own shared library.
    CmmLabel pkg _ _
-    | os == OSMinGW32 -> externalDynamicRefs && (this_pkg /= pkg)
+    | os == OSMinGW32 -> externalDynamicRefs && (toUnitId this_pkg /= pkg)
     | otherwise       -> externalDynamicRefs
 
    LocalBlockLabel _    -> False
diff --git a/compiler/GHC/Cmm/Parser.y b/compiler/GHC/Cmm/Parser.y
index eb1ccae3c6..bb502f8cbe 100644
--- a/compiler/GHC/Cmm/Parser.y
+++ b/compiler/GHC/Cmm/Parser.y
@@ -377,7 +377,7 @@ cmmtop  :: { CmmParse () }
         | cmmdata                       { $1 }
         | decl                          { $1 }
         | 'CLOSURE' '(' NAME ',' NAME lits ')' ';'
-                {% liftP . withHomeUnit $ \pkg ->
+                {% liftP . withHomeUnitId $ \pkg ->
                    do lits <- sequence $6;
                       staticClosure pkg $3 $5 (map getLit lits) }
 
@@ -398,7 +398,7 @@ cmmdata :: { CmmParse () }
 
 data_label :: { CmmParse CLabel }
     : NAME ':'
-                {% liftP . withHomeUnit $ \pkg ->
+                {% liftP . withHomeUnitId $ \pkg ->
                    return (mkCmmDataLabel pkg $1) }
 
 statics :: { [CmmParse [CmmStatic]] }
@@ -455,14 +455,14 @@ maybe_body :: { CmmParse () }
 
 info    :: { CmmParse (CLabel, Maybe CmmInfoTable, [LocalReg]) }
         : NAME
-                {% liftP . withHomeUnit $ \pkg ->
+                {% liftP . withHomeUnitId $ \pkg ->
                    do   newFunctionName $1 pkg
                         return (mkCmmCodeLabel pkg $1, Nothing, []) }
 
 
         | 'INFO_TABLE' '(' NAME ',' INT ',' INT ',' INT ',' STRING ',' STRING ')'
                 -- ptrs, nptrs, closure type, description, type
-                {% liftP . withHomeUnit $ \pkg ->
+                {% liftP . withHomeUnitId $ \pkg ->
                    do dflags <- getDynFlags
                       let prof = profilingInfo dflags $11 $13
                           rep  = mkRTSRep (fromIntegral $9) $
@@ -478,7 +478,7 @@ info    :: { CmmParse (CLabel, Maybe CmmInfoTable, [LocalReg]) }
 
         | 'INFO_TABLE_FUN' '(' NAME ',' INT ',' INT ',' INT ',' STRING ',' STRING ',' INT ')'
                 -- ptrs, nptrs, closure type, description, type, fun type
-                {% liftP . withHomeUnit $ \pkg ->
+                {% liftP . withHomeUnitId $ \pkg ->
                    do dflags <- getDynFlags
                       let prof = profilingInfo dflags $11 $13
                           ty   = Fun 0 (ArgSpec (fromIntegral $15))
@@ -496,7 +496,7 @@ info    :: { CmmParse (CLabel, Maybe CmmInfoTable, [LocalReg]) }
 
         | 'INFO_TABLE_CONSTR' '(' NAME ',' INT ',' INT ',' INT ',' INT ',' STRING ',' STRING ')'
                 -- ptrs, nptrs, tag, closure type, description, type
-                {% liftP . withHomeUnit $ \pkg ->
+                {% liftP . withHomeUnitId $ \pkg ->
                    do dflags <- getDynFlags
                       let prof = profilingInfo dflags $13 $15
                           ty  = Constr (fromIntegral $9)  -- Tag
@@ -515,7 +515,7 @@ info    :: { CmmParse (CLabel, Maybe CmmInfoTable, [LocalReg]) }
 
         | 'INFO_TABLE_SELECTOR' '(' NAME ',' INT ',' INT ',' STRING ',' STRING ')'
                 -- selector, closure type, description, type
-                {% liftP . withHomeUnit $ \pkg ->
+                {% liftP . withHomeUnitId $ \pkg ->
                    do dflags <- getDynFlags
                       let prof = profilingInfo dflags $9 $11
                           ty  = ThunkSelector (fromIntegral $5)
@@ -529,7 +529,7 @@ info    :: { CmmParse (CLabel, Maybe CmmInfoTable, [LocalReg]) }
 
         | 'INFO_TABLE_RET' '(' NAME ',' INT ')'
                 -- closure type (no live regs)
-                {% liftP . withHomeUnit $ \pkg ->
+                {% liftP . withHomeUnitId $ \pkg ->
                    do let prof = NoProfilingInfo
                           rep  = mkRTSRep (fromIntegral $5) $ mkStackRep []
                       return (mkCmmRetLabel pkg $3,
@@ -540,7 +540,7 @@ info    :: { CmmParse (CLabel, Maybe CmmInfoTable, [LocalReg]) }
 
         | 'INFO_TABLE_RET' '(' NAME ',' INT ',' formals0 ')'
                 -- closure type, live regs
-                {% liftP . withHomeUnit $ \pkg ->
+                {% liftP . withHomeUnitId $ \pkg ->
                    do dflags <- getDynFlags
                       let platform = targetPlatform dflags
                       live <- sequence $7
@@ -583,9 +583,9 @@ importName
         | 'CLOSURE' NAME
         { ($2, mkForeignLabel $2 Nothing ForeignLabelInExternalPackage IsData) }
 
-        -- A label imported with an explicit packageId.
+        -- A label imported with an explicit UnitId.
         | STRING NAME
-        { ($2, mkCmmCodeLabel (fsToUnit (mkFastString $1)) $2) }
+        { ($2, mkCmmCodeLabel (UnitId (mkFastString $1)) $2) }
 
 
 names   :: { [FastString] }
@@ -1163,7 +1163,7 @@ profilingInfo dflags desc_str ty_str
     then NoProfilingInfo
     else ProfilingInfo (BS8.pack desc_str) (BS8.pack ty_str)
 
-staticClosure :: Unit -> FastString -> FastString -> [CmmLit] -> CmmParse ()
+staticClosure :: UnitId -> FastString -> FastString -> [CmmLit] -> CmmParse ()
 staticClosure pkg cl_label info payload
   = do dflags <- getDynFlags
        let lits = mkStaticClosure dflags (mkCmmInfoLabel pkg info) dontCareCCS payload [] [] []
diff --git a/compiler/GHC/CoreToStg/Prep.hs b/compiler/GHC/CoreToStg/Prep.hs
index cc408ca46f..44e34aedbf 100644
--- a/compiler/GHC/CoreToStg/Prep.hs
+++ b/compiler/GHC/CoreToStg/Prep.hs
@@ -1556,9 +1556,9 @@ lookupNaturalSDataConName dflags hsc_env = case integerLibrary dflags of
 -- | Helper for 'lookupMkIntegerName', 'lookupIntegerSDataConName'
 guardIntegerUse :: DynFlags -> IO a -> IO a
 guardIntegerUse dflags act
-  | homeUnit dflags == primUnitId
+  | homeUnitId dflags == primUnitId
   = return $ panic "Can't use Integer in ghc-prim"
-  | homeUnit dflags == integerUnitId
+  | homeUnitId dflags == integerUnitId
   = return $ panic "Can't use Integer in integer-*"
   | otherwise = act
 
@@ -1568,11 +1568,11 @@ guardIntegerUse dflags act
 -- literals in `base`. If we do, we get interface loading error for GHC.Natural.
 guardNaturalUse :: DynFlags -> IO a -> IO a
 guardNaturalUse dflags act
-  | homeUnit dflags == primUnitId
+  | homeUnitId dflags == primUnitId
   = return $ panic "Can't use Natural in ghc-prim"
-  | homeUnit dflags == integerUnitId
+  | homeUnitId dflags == integerUnitId
   = return $ panic "Can't use Natural in integer-*"
-  | homeUnit dflags == baseUnitId
+  | homeUnitId dflags == baseUnitId
   = return $ panic "Can't use Natural in base"
   | otherwise = act
 
diff --git a/compiler/GHC/Driver/Backpack.hs b/compiler/GHC/Driver/Backpack.hs
index 2c04fb8b37..9dd5aeba85 100644
--- a/compiler/GHC/Driver/Backpack.hs
+++ b/compiler/GHC/Driver/Backpack.hs
@@ -366,7 +366,7 @@ buildUnit session cid insts lunit = do
 
 compileExe :: LHsUnit HsComponentId -> BkpM ()
 compileExe lunit = do
-    msgUnitId mainUnitId
+    msgUnitId mainUnit
     let deps_w_rns = hsunitDeps False (unLoc lunit)
         deps = map fst deps_w_rns
         -- no renaming necessary
diff --git a/compiler/GHC/Driver/CodeOutput.hs b/compiler/GHC/Driver/CodeOutput.hs
index db9b331d34..e9ac354090 100644
--- a/compiler/GHC/Driver/CodeOutput.hs
+++ b/compiler/GHC/Driver/CodeOutput.hs
@@ -131,7 +131,7 @@ outputC dflags filenm cmm_stream packages
          --   * -#include options from the cmdline and OPTIONS pragmas
          --   * the _stub.h file, if there is one.
          --
-         let rts = unsafeLookupUnit (pkgState dflags) rtsUnitId
+         let rts = unsafeLookupUnitId (pkgState dflags) rtsUnitId
 
          let cc_injects = unlines (map mk_include (unitIncludes rts))
              mk_include h_file =
@@ -223,7 +223,7 @@ outputForeignStubs dflags mod location stubs
 
         -- we need the #includes from the rts package for the stub files
         let rts_includes =
-               let rts_pkg = unsafeLookupUnit (pkgState dflags) rtsUnitId in
+               let rts_pkg = unsafeLookupUnitId (pkgState dflags) rtsUnitId in
                concatMap mk_include (unitIncludes rts_pkg)
             mk_include i = "#include \"" ++ i ++ "\"\n"
 
diff --git a/compiler/GHC/Driver/Finder.hs b/compiler/GHC/Driver/Finder.hs
index 09ef8e2d25..c3332a663c 100644
--- a/compiler/GHC/Driver/Finder.hs
+++ b/compiler/GHC/Driver/Finder.hs
@@ -345,7 +345,7 @@ findPackageModule hsc_env mod = do
         pkg_id = moduleUnit mod
         pkgstate = pkgState dflags
   --
-  case lookupInstalledPackage pkgstate pkg_id of
+  case lookupUnitId pkgstate pkg_id of
      Nothing -> return (InstalledNoPackage pkg_id)
      Just pkg_conf -> findPackageModule_ hsc_env mod pkg_conf
 
diff --git a/compiler/GHC/Driver/Main.hs b/compiler/GHC/Driver/Main.hs
index e5381e188f..5d9abc254a 100644
--- a/compiler/GHC/Driver/Main.hs
+++ b/compiler/GHC/Driver/Main.hs
@@ -1218,7 +1218,7 @@ checkPkgTrust pkgs = do
     let errors = S.foldr go [] pkgs
         state  = pkgState dflags
         go pkg acc
-            | unitIsTrusted $ getInstalledPackageDetails state pkg
+            | unitIsTrusted $ unsafeLookupUnitId state pkg
             = acc
             | otherwise
             = (:acc) $ mkErrMsg dflags noSrcSpan (pkgQual state)
diff --git a/compiler/GHC/Driver/Pipeline.hs b/compiler/GHC/Driver/Pipeline.hs
index bbc44a4653..5465ebefd9 100644
--- a/compiler/GHC/Driver/Pipeline.hs
+++ b/compiler/GHC/Driver/Pipeline.hs
@@ -515,7 +515,7 @@ linkingNeeded dflags staticLink linkables pkg_deps = do
         -- not extra_libraries or -l things from the command line.
         let pkgstate = pkgState dflags
         let pkg_hslibs  = [ (collectLibraryPaths dflags [c], lib)
-                          | Just c <- map (lookupInstalledPackage pkgstate) pkg_deps,
+                          | Just c <- map (lookupUnitId pkgstate) pkg_deps,
                             lib <- packageHsLibs dflags c ]
 
         pkg_libfiles <- mapM (uncurry (findHSLib dflags)) pkg_hslibs
@@ -1312,7 +1312,7 @@ runPhase (RealPhase cc_phase) input_fn dflags
                 -- way we do the import depends on whether we're currently compiling
                 -- the base package or not.
                        ++ (if platformOS platform == OSMinGW32 &&
-                              homeUnit dflags == baseUnitId
+                              homeUnitId dflags == baseUnitId
                                 then [ "-DCOMPILING_BASE_PACKAGE" ]
                                 else [])
 
@@ -2223,7 +2223,7 @@ getGhcVersionPathName dflags = do
   candidates <- case ghcVersionFile dflags of
     Just path -> return [path]
     Nothing -> (map (</> "ghcversion.h")) <$>
-               (getPackageIncludePath dflags [toUnitId rtsUnitId])
+               (getPackageIncludePath dflags [rtsUnitId])
 
   found <- filterM doesFileExist candidates
   case found of
diff --git a/compiler/GHC/Driver/Session.hs b/compiler/GHC/Driver/Session.hs
index 694874a179..9f4c30096e 100644
--- a/compiler/GHC/Driver/Session.hs
+++ b/compiler/GHC/Driver/Session.hs
@@ -1329,7 +1329,7 @@ defaultDynFlags mySettings llvmConfig =
         reductionDepth          = treatZeroAsInf mAX_REDUCTION_DEPTH,
         solverIterations        = treatZeroAsInf mAX_SOLVER_ITERATIONS,
 
-        homeUnitId              = toUnitId mainUnitId,
+        homeUnitId              = mainUnitId,
         homeUnitInstanceOfId    = Nothing,
         homeUnitInstantiations  = [],
 
@@ -1980,7 +1980,7 @@ homeUnit dflags =
          -- detect fully indefinite units: all their instantiations are hole
          -- modules and the home unit id is the same as the instantiating unit
          -- id (see Note [About units] in GHC.Unit)
-         | all (isHoleModule . snd) is && u == homeUnitId dflags
+         | all (isHoleModule . snd) is && indefUnit u == homeUnitId dflags
          -> mkVirtUnit (updateIndefUnitId (pkgState dflags) u) is
          -- otherwise it must be that we compile a fully definite units
          -- TODO: error when the unit is partially instantiated??
@@ -4637,10 +4637,10 @@ setMainIs arg
   | not (null main_fn) && isLower (head main_fn)
      -- The arg looked like "Foo.Bar.baz"
   = upd $ \d -> d { mainFunIs = Just main_fn,
-                   mainModIs = mkModule mainUnitId (mkModuleName main_mod) }
+                   mainModIs = mkModule mainUnit (mkModuleName main_mod) }
 
   | isUpper (head arg)  -- The arg looked like "Foo" or "Foo.Bar"
-  = upd $ \d -> d { mainModIs = mkModule mainUnitId (mkModuleName arg) }
+  = upd $ \d -> d { mainModIs = mkModule mainUnit (mkModuleName arg) }
 
   | otherwise                   -- The arg looked like "baz"
   = upd $ \d -> d { mainFunIs = Just arg }
diff --git a/compiler/GHC/Driver/Types.hs b/compiler/GHC/Driver/Types.hs
index 1b5591793b..3ddd4b1b26 100644
--- a/compiler/GHC/Driver/Types.hs
+++ b/compiler/GHC/Driver/Types.hs
@@ -1852,7 +1852,7 @@ shadowed_by ids = shadowed
 setInteractivePackage :: HscEnv -> HscEnv
 setInteractivePackage hsc_env
    = hsc_env { hsc_dflags = (hsc_dflags hsc_env)
-                { homeUnitId = toUnitId interactiveUnitId } }
+                { homeUnitId = interactiveUnitId } }
 
 setInteractivePrintName :: InteractiveContext -> Name -> InteractiveContext
 setInteractivePrintName ic n = ic{ic_int_print = n}
@@ -2030,7 +2030,7 @@ mkQualModule dflags mod
 -- with a unit id if the package ID would be ambiguous.
 mkQualPackage :: PackageState -> QueryQualifyPackage
 mkQualPackage pkgs uid
-     | uid == mainUnitId || uid == interactiveUnitId
+     | uid == mainUnit || uid == interactiveUnit
         -- Skip the lookup if it's main, since it won't be in the package
         -- database!
      = False
diff --git a/compiler/GHC/HsToCore/Coverage.hs b/compiler/GHC/HsToCore/Coverage.hs
index 81b95fba67..816768cc09 100644
--- a/compiler/GHC/HsToCore/Coverage.hs
+++ b/compiler/GHC/HsToCore/Coverage.hs
@@ -180,7 +180,7 @@ writeMixEntries dflags mod count entries filename
             mod_name = moduleNameString (moduleName mod)
 
             hpc_mod_dir
-              | moduleUnit mod == mainUnitId  = hpc_dir
+              | moduleUnit mod == mainUnit  = hpc_dir
               | otherwise = hpc_dir ++ "/" ++ unitString (moduleUnit mod)
 
             tabStop = 8 -- <tab> counts as a normal char in GHC's
@@ -1337,7 +1337,7 @@ hpcInitCode this_mod (HpcInfo tickCount hashNo)
     package_name = hcat (map (text.charToC) $ BS.unpack $
                          bytesFS (unitFS  (moduleUnit this_mod)))
     full_name_str
-       | moduleUnit this_mod == mainUnitId
+       | moduleUnit this_mod == mainUnit
        = module_name
        | otherwise
        = package_name <> char '/' <> module_name
diff --git a/compiler/GHC/HsToCore/Usage.hs b/compiler/GHC/HsToCore/Usage.hs
index 97ab4ba89a..c68248744f 100644
--- a/compiler/GHC/HsToCore/Usage.hs
+++ b/compiler/GHC/HsToCore/Usage.hs
@@ -86,7 +86,7 @@ mkDependencies iuid pluginModules
 
           raw_pkgs = foldr Set.insert (imp_dep_pkgs imports) plugin_dep_pkgs
 
-          pkgs | th_used   = Set.insert (toUnitId thUnitId) raw_pkgs
+          pkgs | th_used   = Set.insert thUnitId raw_pkgs
                | otherwise = raw_pkgs
 
           -- Set the packages required to be Safe according to Safe Haskell.
diff --git a/compiler/GHC/Parser/Lexer.x b/compiler/GHC/Parser/Lexer.x
index 542af41557..6778d5aa3f 100644
--- a/compiler/GHC/Parser/Lexer.x
+++ b/compiler/GHC/Parser/Lexer.x
@@ -55,7 +55,7 @@ module GHC.Parser.Lexer (
    appendError,
    allocateComments,
    MonadP(..),
-   getRealSrcLoc, getPState, withHomeUnit,
+   getRealSrcLoc, getPState, withHomeUnitId,
    failMsgP, failLocMsgP, srcParseFail,
    getErrorMessages, getMessages,
    popContext, pushModuleContext, setLastToken, setSrcLoc,
@@ -2088,7 +2088,7 @@ warnopt f options = f `EnumSet.member` pWarningFlags options
 -- See 'mkParserFlags' or 'mkParserFlags'' for ways to construct this.
 data ParserFlags = ParserFlags {
     pWarningFlags   :: EnumSet WarningFlag
-  , pHomeUnit       :: Unit        -- ^ unit currently being compiled
+  , pHomeUnitId     :: UnitId      -- ^ unit currently being compiled
   , pExtsBitmap     :: !ExtsBitmap -- ^ bitmap of permitted extensions
   }
 
@@ -2183,8 +2183,8 @@ failLocMsgP loc1 loc2 str =
 getPState :: P PState
 getPState = P $ \s -> POk s s
 
-withHomeUnit :: (Unit -> a) -> P a
-withHomeUnit f = P $ \s@(PState{options = o}) -> POk s (f (pHomeUnit o))
+withHomeUnitId :: (UnitId -> a) -> P a
+withHomeUnitId f = P $ \s@(PState{options = o}) -> POk s (f (pHomeUnitId o))
 
 getExts :: P ExtsBitmap
 getExts = P $ \s -> POk s (pExtsBitmap . options $ s)
@@ -2500,7 +2500,7 @@ pragState dynflags buf loc = (mkPState dynflags buf loc) {
 mkParserFlags'
   :: EnumSet WarningFlag        -- ^ warnings flags enabled
   -> EnumSet LangExt.Extension  -- ^ permitted language extensions enabled
-  -> Unit                       -- ^ key of package currently being compiled
+  -> UnitId                     -- ^ id of the unit currently being compiled
   -> Bool                       -- ^ are safe imports on?
   -> Bool                       -- ^ keeping Haddock comment tokens
   -> Bool                       -- ^ keep regular comment tokens
@@ -2512,11 +2512,11 @@ mkParserFlags'
 
   -> ParserFlags
 -- ^ Given exactly the information needed, set up the 'ParserFlags'
-mkParserFlags' warningFlags extensionFlags homeUnit
+mkParserFlags' warningFlags extensionFlags homeUnitId
   safeImports isHaddock rawTokStream usePosPrags =
     ParserFlags {
       pWarningFlags = warningFlags
-    , pHomeUnit     = homeUnit
+    , pHomeUnitId   = homeUnitId
     , pExtsBitmap   = safeHaskellBit .|. langExtBits .|. optBits
     }
   where
@@ -2578,7 +2578,7 @@ mkParserFlags =
   mkParserFlags'
     <$> DynFlags.warningFlags
     <*> DynFlags.extensionFlags
-    <*> DynFlags.homeUnit
+    <*> DynFlags.homeUnitId
     <*> safeImportsOn
     <*> gopt Opt_Haddock
     <*> gopt Opt_KeepRawTokenStream
diff --git a/compiler/GHC/Runtime/Linker.hs b/compiler/GHC/Runtime/Linker.hs
index 22cd871fad..e45fce9bcc 100644
--- a/compiler/GHC/Runtime/Linker.hs
+++ b/compiler/GHC/Runtime/Linker.hs
@@ -143,7 +143,7 @@ emptyPLS = PersistentLinkerState
   --
   -- The linker's symbol table is populated with RTS symbols using an
   -- explicit list.  See rts/Linker.c for details.
-  where init_pkgs = map toUnitId [rtsUnitId]
+  where init_pkgs = [rtsUnitId]
 
 extendLoadedPkgs :: DynLinker -> [UnitId] -> IO ()
 extendLoadedPkgs dl pkgs =
@@ -1261,7 +1261,7 @@ linkPackages' hsc_env new_pks pls = do
         | new_pkg `elem` pkgs   -- Already linked
         = return pkgs
 
-        | Just pkg_cfg <- lookupInstalledPackage pkgstate new_pkg
+        | Just pkg_cfg <- lookupUnitId pkgstate new_pkg
         = do {  -- Link dependents first
                pkgs' <- link pkgs (unitDepends pkg_cfg)
                 -- Now link the package itself
diff --git a/compiler/GHC/StgToCmm/ExtCode.hs b/compiler/GHC/StgToCmm/ExtCode.hs
index 49f6a21b9c..e0b20021b3 100644
--- a/compiler/GHC/StgToCmm/ExtCode.hs
+++ b/compiler/GHC/StgToCmm/ExtCode.hs
@@ -61,7 +61,7 @@ data Named
         = VarN CmmExpr          -- ^ Holds CmmLit(CmmLabel ..) which gives the label type,
                                 --      eg, RtsLabel, ForeignLabel, CmmLabel etc.
 
-        | FunN   Unit           -- ^ A function name from this package
+        | FunN   UnitId         -- ^ A function name from this unit
         | LabelN BlockId        -- ^ A blockid of some code or data.
 
 -- | An environment of named things.
@@ -165,7 +165,7 @@ newLabel name = do
 -- | Add add a local function to the environment.
 newFunctionName
         :: FastString   -- ^ name of the function
-        -> Unit         -- ^ package of the current module
+        -> UnitId       -- ^ package of the current module
         -> ExtCode
 
 newFunctionName name pkg = addDecl name (FunN pkg)
@@ -204,7 +204,7 @@ lookupName name = do
   return $
      case lookupUFM env name of
         Just (VarN e)   -> e
-        Just (FunN pkg) -> CmmLit (CmmLabel (mkCmmCodeLabel pkg          name))
+        Just (FunN uid) -> CmmLit (CmmLabel (mkCmmCodeLabel uid       name))
         _other          -> CmmLit (CmmLabel (mkCmmCodeLabel rtsUnitId name))
 
 
diff --git a/compiler/GHC/StgToCmm/Prim.hs b/compiler/GHC/StgToCmm/Prim.hs
index b0f9fddad6..e70f50ee84 100644
--- a/compiler/GHC/StgToCmm/Prim.hs
+++ b/compiler/GHC/StgToCmm/Prim.hs
@@ -42,7 +42,7 @@ import GHC.Cmm.BlockId
 import GHC.Cmm.Graph
 import GHC.Stg.Syntax
 import GHC.Cmm
-import GHC.Unit         ( rtsUnitId )
+import GHC.Unit         ( rtsUnit )
 import GHC.Core.Type    ( Type, tyConAppTyCon )
 import GHC.Core.TyCon
 import GHC.Cmm.CLabel
@@ -3043,7 +3043,7 @@ emitCopyUpdRemSetPush platform hdr_size dst dst_off n =
         emit graph
   where
     lbl = mkLblExpr $ mkPrimCallLabel
-          $ PrimCall (fsLit "stg_copyArray_barrier") rtsUnitId
+          $ PrimCall (fsLit "stg_copyArray_barrier") rtsUnit
     args =
       [ mkIntExpr platform hdr_size
       , dst
diff --git a/compiler/GHC/StgToCmm/Utils.hs b/compiler/GHC/StgToCmm/Utils.hs
index 3815c2b698..6367f5e839 100644
--- a/compiler/GHC/StgToCmm/Utils.hs
+++ b/compiler/GHC/StgToCmm/Utils.hs
@@ -180,10 +180,10 @@ tagToClosure platform tycon tag
 --
 -------------------------------------------------------------------------
 
-emitRtsCall :: Unit -> FastString -> [(CmmExpr,ForeignHint)] -> Bool -> FCode ()
+emitRtsCall :: UnitId -> FastString -> [(CmmExpr,ForeignHint)] -> Bool -> FCode ()
 emitRtsCall pkg fun args safe = emitRtsCallGen [] (mkCmmCodeLabel pkg fun) args safe
 
-emitRtsCallWithResult :: LocalReg -> ForeignHint -> Unit -> FastString
+emitRtsCallWithResult :: LocalReg -> ForeignHint -> UnitId -> FastString
         -> [(CmmExpr,ForeignHint)] -> Bool -> FCode ()
 emitRtsCallWithResult res hint pkg fun args safe
    = emitRtsCallGen [(res,hint)] (mkCmmCodeLabel pkg fun) args safe
diff --git a/compiler/GHC/SysTools.hs b/compiler/GHC/SysTools.hs
index 036220b7c1..04bfea46ce 100644
--- a/compiler/GHC/SysTools.hs
+++ b/compiler/GHC/SysTools.hs
@@ -276,7 +276,7 @@ linkDynLib dflags0 o_files dep_packages
                       OSMinGW32 ->
                           pkgs
                       _ ->
-                          filter ((/= rtsUnitId) . mkUnit) pkgs
+                          filter ((/= rtsUnitId) . unitId) pkgs
     let pkg_link_opts = let (package_hs_libs, extra_libs, other_flags) = collectLinkOpts dflags pkgs_no_rts
                         in  package_hs_libs ++ extra_libs ++ other_flags
 
diff --git a/compiler/GHC/SysTools/ExtraObj.hs b/compiler/GHC/SysTools/ExtraObj.hs
index ef04468ebd..789a3ed661 100644
--- a/compiler/GHC/SysTools/ExtraObj.hs
+++ b/compiler/GHC/SysTools/ExtraObj.hs
@@ -57,7 +57,7 @@ mkExtraObj dflags extn xs
       -- set of include directories and PIC flags.
       cOpts = map Option (picCCOpts dflags)
                     ++ map (FileOption "-I")
-                            (unitIncludeDirs $ unsafeLookupUnit pkgs rtsUnitId)
+                            (unitIncludeDirs $ unsafeLookupUnit pkgs rtsUnit)
 
       -- When compiling assembler code, we drop the usual C options, and if the
       -- compiler is Clang, we add an extra argument to tell Clang to ignore
diff --git a/compiler/GHC/Tc/Errors.hs b/compiler/GHC/Tc/Errors.hs
index 41bc8cd269..d38b7adcbd 100644
--- a/compiler/GHC/Tc/Errors.hs
+++ b/compiler/GHC/Tc/Errors.hs
@@ -2174,7 +2174,7 @@ sameOccExtra ty1 ty2
       | otherwise  -- Imported things have an UnhelpfulSrcSpan
       = hang (quotes (ppr nm))
            2 (sep [ text "is defined in" <+> quotes (ppr (moduleName mod))
-                  , ppUnless (same_pkg || pkg == mainUnitId) $
+                  , ppUnless (same_pkg || pkg == mainUnit) $
                     nest 4 $ text "in package" <+> quotes (ppr pkg) ])
        where
          pkg = moduleUnit mod
diff --git a/compiler/GHC/Tc/Utils/Backpack.hs b/compiler/GHC/Tc/Utils/Backpack.hs
index 66733b0618..5643ec05fb 100644
--- a/compiler/GHC/Tc/Utils/Backpack.hs
+++ b/compiler/GHC/Tc/Utils/Backpack.hs
@@ -568,7 +568,7 @@ mergeSignatures
             let insts = instUnitInsts iuid
                 isFromSignaturePackage =
                     let inst_uid = instUnitInstanceOf iuid
-                        pkg = getInstalledPackageDetails pkgstate (indefUnit inst_uid)
+                        pkg = unsafeLookupUnitId pkgstate (indefUnit inst_uid)
                     in null (unitExposedModules pkg)
             -- 3(a). Rename the exports according to how the dependency
             -- was instantiated.  The resulting export list will be accurate
diff --git a/compiler/GHC/Tc/Utils/Monad.hs b/compiler/GHC/Tc/Utils/Monad.hs
index 5030c61fd3..ca85a087b6 100644
--- a/compiler/GHC/Tc/Utils/Monad.hs
+++ b/compiler/GHC/Tc/Utils/Monad.hs
@@ -265,7 +265,7 @@ initTc hsc_env hsc_src keep_rn_syntax mod loc do_this
                 tcg_rdr_env        = emptyGlobalRdrEnv,
                 tcg_fix_env        = emptyNameEnv,
                 tcg_field_env      = emptyNameEnv,
-                tcg_default        = if moduleUnit mod == primUnitId
+                tcg_default        = if moduleUnit mod == primUnit
                                      then Just []  -- See Note [Default types]
                                      else Nothing,
                 tcg_type_env       = emptyNameEnv,
diff --git a/compiler/GHC/Unit/Info.hs b/compiler/GHC/Unit/Info.hs
index 917c55bca6..d348f7e9e2 100644
--- a/compiler/GHC/Unit/Info.hs
+++ b/compiler/GHC/Unit/Info.hs
@@ -167,9 +167,9 @@ expandedUnitInfoId p =
 
 definiteUnitInfoId :: UnitInfo -> Maybe DefUnitId
 definiteUnitInfoId p =
-    case mkUnit p of
-        RealUnit def_uid -> Just def_uid
-        _               -> Nothing
+    if unitIsIndefinite p
+       then Nothing
+       else Just (Definite (unitId p))
 
 -- | Create a UnitPprInfo from a UnitInfo
 mkUnitPprInfo :: GenUnitInfo u -> UnitPprInfo
diff --git a/compiler/GHC/Unit/State.hs b/compiler/GHC/Unit/State.hs
index 64c4fdaee2..7f81605435 100644
--- a/compiler/GHC/Unit/State.hs
+++ b/compiler/GHC/Unit/State.hs
@@ -21,12 +21,14 @@ module GHC.Unit.State (
         -- * Querying the package config
         lookupUnit,
         lookupUnit',
-        lookupInstalledPackage,
+        unsafeLookupUnit,
+        lookupUnitId,
+        lookupUnitId',
+        unsafeLookupUnitId,
+
         lookupPackageName,
         improveUnit,
         searchPackageId,
-        unsafeLookupUnit,
-        getInstalledPackageDetails,
         displayUnitId,
         listVisibleModuleNames,
         lookupModuleInAllPackages,
@@ -393,7 +395,7 @@ type InstalledPackageIndex = Map UnitId UnitInfo
 emptyUnitInfoMap :: UnitInfoMap
 emptyUnitInfoMap = UnitInfoMap emptyUDFM emptyUniqSet
 
--- | Find the unit we know about with the given unit id, if any
+-- | Find the unit we know about with the given unit, if any
 lookupUnit :: PackageState -> Unit -> Maybe UnitInfo
 lookupUnit pkgs = lookupUnit' (allowVirtualUnits pkgs) (unitInfoMap pkgs)
 
@@ -409,6 +411,28 @@ lookupUnit' True m@(UnitInfoMap pkg_map _) uid = case uid of
    VirtUnit i -> fmap (renamePackage m (instUnitInsts i))
                       (lookupUDFM pkg_map (instUnitInstanceOf i))
 
+-- | Find the unit we know about with the given unit id, if any
+lookupUnitId :: PackageState -> UnitId -> Maybe UnitInfo
+lookupUnitId state uid = lookupUnitId' (unitInfoMap state) uid
+
+-- | Find the unit we know about with the given unit id, if any
+lookupUnitId' :: UnitInfoMap -> UnitId -> Maybe UnitInfo
+lookupUnitId' (UnitInfoMap db _) uid = lookupUDFM db uid
+
+
+-- | Looks up the given unit in the package state, panicing if it is not found
+unsafeLookupUnit :: HasDebugCallStack => PackageState -> Unit -> UnitInfo
+unsafeLookupUnit state u = case lookupUnit state u of
+   Just info -> info
+   Nothing   -> pprPanic "unsafeLookupUnit" (ppr u)
+
+-- | Looks up the given unit id in the package state, panicing if it is not found
+unsafeLookupUnitId :: HasDebugCallStack => PackageState -> UnitId -> UnitInfo
+unsafeLookupUnitId state uid = case lookupUnitId state uid of
+   Just info -> info
+   Nothing   -> pprPanic "unsafeLookupUnitId" (ppr uid)
+
+
 -- | Find the package we know about with the given package name (e.g. @foo@), if any
 -- (NB: there might be a locally defined unit name which overrides this)
 lookupPackageName :: PackageState -> PackageName -> Maybe IndefUnitId
@@ -429,26 +453,6 @@ extendUnitInfoMap (UnitInfoMap pkg_map closure) new_pkgs
   where add pkg_map p = addToUDFM (addToUDFM pkg_map (expandedUnitInfoId p) p)
                                   (unitId p) p
 
--- | Looks up the package with the given id in the package state, panicing if it is
--- not found
-unsafeLookupUnit :: HasDebugCallStack => PackageState -> Unit -> UnitInfo
-unsafeLookupUnit pkgs pid =
-    case lookupUnit pkgs pid of
-      Just info -> info
-      Nothing   -> pprPanic "unsafeLookupUnit" (ppr pid)
-
-lookupInstalledPackage :: PackageState -> UnitId -> Maybe UnitInfo
-lookupInstalledPackage pkgstate uid = lookupInstalledPackage' (unitInfoMap pkgstate) uid
-
-lookupInstalledPackage' :: UnitInfoMap -> UnitId -> Maybe UnitInfo
-lookupInstalledPackage' (UnitInfoMap db _) uid = lookupUDFM db uid
-
-getInstalledPackageDetails :: HasDebugCallStack => PackageState -> UnitId -> UnitInfo
-getInstalledPackageDetails pkgstate uid =
-    case lookupInstalledPackage pkgstate uid of
-      Just config -> config
-      Nothing -> pprPanic "getInstalledPackageDetails" (ppr uid)
-
 -- | Get a list of entries from the package database.  NB: be careful with
 -- this function, although all packages in this map are "visible", this
 -- does not imply that the exposed-modules of the package are available
@@ -945,12 +949,9 @@ pprTrustFlag flag = case flag of
 --
 -- See Note [Wired-in units] in GHC.Unit.Module
 
-type WiredInUnitId = String
+type WiredInUnitId = UnitId
 type WiredPackagesMap = Map WiredUnitId WiredUnitId
 
-wired_in_unitids :: [WiredInUnitId]
-wired_in_unitids = map unitString wiredInUnitIds
-
 findWiredInPackages
    :: DynFlags
    -> PackagePrecedenceIndex
@@ -968,9 +969,9 @@ findWiredInPackages dflags prec_map pkgs vis_map = do
         matches :: UnitInfo -> WiredInUnitId -> Bool
         pc `matches` pid
             -- See Note [The integer library] in GHC.Builtin.Names
-            | pid == unitString integerUnitId
+            | pid == integerUnitId
             = unitPackageNameString pc `elem` ["integer-gmp", "integer-simple"]
-        pc `matches` pid = unitPackageNameString pc == pid
+        pc `matches` pid = unitPackageName pc == PackageName (unitIdFS pid)
 
         -- find which package corresponds to each wired-in package
         -- delete any other packages with the same name
@@ -1005,7 +1006,7 @@ findWiredInPackages dflags prec_map pkgs vis_map = do
                 notfound = do
                           debugTraceMsg dflags 2 $
                             text "wired-in package "
-                                 <> text wired_pkg
+                                 <> ftext (unitIdFS wired_pkg)
                                  <> text " not found."
                           return Nothing
                 pick :: UnitInfo
@@ -1013,20 +1014,20 @@ findWiredInPackages dflags prec_map pkgs vis_map = do
                 pick pkg = do
                         debugTraceMsg dflags 2 $
                             text "wired-in package "
-                                 <> text wired_pkg
+                                 <> ftext (unitIdFS wired_pkg)
                                  <> text " mapped to "
                                  <> ppr (unitId pkg)
                         return (Just (wired_pkg, pkg))
 
 
-  mb_wired_in_pkgs <- mapM (findWiredInPackage pkgs) wired_in_unitids
+  mb_wired_in_pkgs <- mapM (findWiredInPackage pkgs) wiredInUnitIds
   let
         wired_in_pkgs = catMaybes mb_wired_in_pkgs
         pkgstate = pkgState dflags
 
         wiredInMap :: Map WiredUnitId WiredUnitId
         wiredInMap = Map.fromList
-          [ (key, Definite (stringToUnitId wiredInUnitId))
+          [ (key, Definite wiredInUnitId)
           | (wiredInUnitId, pkg) <- wired_in_pkgs
           , Just key <- pure $ definiteUnitInfoId pkg
           ]
@@ -1542,7 +1543,8 @@ mkPackageState dflags dbs preload0 = do
       -- add base & rts to the preload packages
       basicLinkedPackages
        | gopt Opt_AutoLinkPackages dflags
-          = filter (flip elemUDFM (unUnitInfoMap pkg_db))
+          = fmap (RealUnit . Definite) $
+            filter (flip elemUDFM (unUnitInfoMap pkg_db))
                 [baseUnitId, rtsUnitId]
        | otherwise = []
       -- but in any case remove the current package from the set of
@@ -1991,7 +1993,7 @@ getPreloadPackagesAnd dflags pkgids0 =
       pairs = zip pkgids (repeat Nothing)
   in do
   all_pkgs <- throwErr dflags (foldM (add_package dflags pkg_map) preload pairs)
-  return (map (getInstalledPackageDetails state) all_pkgs)
+  return (map (unsafeLookupUnitId state) all_pkgs)
 
 -- Takes a list of packages, and returns the list with dependencies included,
 -- in reverse dependency order (a package appears before those it depends on).
@@ -2023,7 +2025,7 @@ add_package :: DynFlags
 add_package dflags pkg_db ps (p, mb_parent)
   | p `elem` ps = return ps     -- Check if we've already added this package
   | otherwise =
-      case lookupInstalledPackage' pkg_db p of
+      case lookupUnitId' pkg_db p of
         Nothing -> Failed (missingPackageMsg p <>
                            missingDependencyMsg mb_parent)
         Just pkg -> do
@@ -2062,7 +2064,7 @@ missingDependencyMsg (Just parent)
 mkIndefUnitId :: PackageState -> FastString -> IndefUnitId
 mkIndefUnitId pkgstate raw =
     let uid = UnitId raw
-    in case lookupInstalledPackage pkgstate uid of
+    in case lookupUnitId pkgstate uid of
          Nothing -> Indefinite uid Nothing -- we didn't find the unit at all
          Just c  -> Indefinite uid $ Just $ mkUnitPprInfo c
 
@@ -2073,7 +2075,7 @@ updateIndefUnitId pkgstate uid = mkIndefUnitId pkgstate (unitIdFS (indefUnit uid
 
 displayUnitId :: PackageState -> UnitId -> Maybe String
 displayUnitId pkgstate uid =
-    fmap unitPackageIdString (lookupInstalledPackage pkgstate uid)
+    fmap unitPackageIdString (lookupUnitId pkgstate uid)
 
 -- -----------------------------------------------------------------------------
 -- Displaying packages
diff --git a/compiler/GHC/Unit/Types.hs b/compiler/GHC/Unit/Types.hs
index 6e04526607..63816d5b09 100644
--- a/compiler/GHC/Unit/Types.hs
+++ b/compiler/GHC/Unit/Types.hs
@@ -62,6 +62,16 @@ module GHC.Unit.Types
    , mainUnitId
    , thisGhcUnitId
    , interactiveUnitId
+
+   , primUnit
+   , integerUnit
+   , baseUnit
+   , rtsUnit
+   , thUnit
+   , mainUnit
+   , thisGhcUnit
+   , interactiveUnit
+
    , isInteractiveModule
    , wiredInUnitIds
 
@@ -162,7 +172,7 @@ pprModule mod@(Module p n)  = getPprStyle doc
  where
   doc sty
     | codeStyle sty =
-        (if p == mainUnitId
+        (if p == mainUnit
                 then empty -- never qualify the main package in code
                 else ztext (zEncodeFS (unitFS p)) <> char '_')
             <> pprModuleName n
@@ -612,27 +622,38 @@ For `integer-gmp`/`integer-simple` we also change the base name to
 See Note [The integer library] in "GHC.Builtin.Names".
 -}
 
-integerUnitId, primUnitId,
-  baseUnitId, rtsUnitId,
-  thUnitId, mainUnitId, thisGhcUnitId, interactiveUnitId  :: Unit
-primUnitId        = fsToUnit (fsLit "ghc-prim")
-integerUnitId     = fsToUnit (fsLit "integer-wired-in")
-   -- See Note [The integer library] in "GHC.Builtin.Names"
-baseUnitId        = fsToUnit (fsLit "base")
-rtsUnitId         = fsToUnit (fsLit "rts")
-thUnitId          = fsToUnit (fsLit "template-haskell")
-thisGhcUnitId     = fsToUnit (fsLit "ghc")
-interactiveUnitId = fsToUnit (fsLit "interactive")
+integerUnitId, primUnitId, baseUnitId, rtsUnitId,
+  thUnitId, mainUnitId, thisGhcUnitId, interactiveUnitId  :: UnitId
+
+integerUnit, primUnit, baseUnit, rtsUnit,
+  thUnit, mainUnit, thisGhcUnit, interactiveUnit  :: Unit
+
+primUnitId        = UnitId (fsLit "ghc-prim")
+integerUnitId     = UnitId (fsLit "integer-wired-in")
+baseUnitId        = UnitId (fsLit "base")
+rtsUnitId         = UnitId (fsLit "rts")
+thisGhcUnitId     = UnitId (fsLit "ghc")
+interactiveUnitId = UnitId (fsLit "interactive")
+thUnitId          = UnitId (fsLit "template-haskell")
+
+thUnit            = RealUnit (Definite thUnitId)
+primUnit          = RealUnit (Definite primUnitId)
+integerUnit       = RealUnit (Definite integerUnitId)
+baseUnit          = RealUnit (Definite baseUnitId)
+rtsUnit           = RealUnit (Definite rtsUnitId)
+thisGhcUnit       = RealUnit (Definite thisGhcUnitId)
+interactiveUnit   = RealUnit (Definite interactiveUnitId)
 
 -- | This is the package Id for the current program.  It is the default
 -- package Id if you don't specify a package name.  We don't add this prefix
 -- to symbol names, since there can be only one main package per program.
-mainUnitId      = fsToUnit (fsLit "main")
+mainUnitId = UnitId (fsLit "main")
+mainUnit = RealUnit (Definite mainUnitId)
 
 isInteractiveModule :: Module -> Bool
-isInteractiveModule mod = moduleUnit mod == interactiveUnitId
+isInteractiveModule mod = moduleUnit mod == interactiveUnit
 
-wiredInUnitIds :: [Unit]
+wiredInUnitIds :: [UnitId]
 wiredInUnitIds =
    [ primUnitId
    , integerUnitId