basicTypes/OccName.hs

    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
    -}

    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE BangPatterns #-}
    {-# LANGUAGE OverloadedStrings #-}

    -- |
    -- #name_types#
    -- GHC uses several kinds of name internally:
    --
    -- * 'OccName.OccName' represents names as strings with just a little more information:
    --   the \"namespace\" that the name came from, e.g. the namespace of value, type constructors or
    --   data constructors
    --
    -- * 'RdrName.RdrName': see "RdrName#name_types"
    --
    -- * 'Name.Name': see "Name#name_types"
    --
    -- * 'Id.Id': see "Id#name_types"
    --
    -- * 'Var.Var': see "Var#name_types"

    module OccName (
            -- * The 'NameSpace' type
            NameSpace, -- Abstract

            nameSpacesRelated,

            -- ** Construction
            -- $real_vs_source_data_constructors
            tcName, clsName, tcClsName, dataName, varName,
            tvName, srcDataName,

            -- ** Pretty Printing
            pprNameSpace, pprNonVarNameSpace, pprNameSpaceBrief,

            -- * The 'OccName' type
            OccName,        -- Abstract, instance of Outputable
            pprOccName,

            -- ** Construction
            mkOccName, mkOccNameFS,
            mkVarOcc, mkVarOccFS,
            mkDataOcc, mkDataOccFS,
            mkTyVarOcc, mkTyVarOccFS,
            mkTcOcc, mkTcOccFS,
            mkClsOcc, mkClsOccFS,
            mkDFunOcc,
            setOccNameSpace,
            demoteOccName,
            HasOccName(..),

            -- ** Derived 'OccName's
            isDerivedOccName,
            mkDataConWrapperOcc, mkWorkerOcc,
            mkMatcherOcc, mkBuilderOcc,
            mkDefaultMethodOcc, isDefaultMethodOcc, isTypeableBindOcc,
            mkNewTyCoOcc, mkClassOpAuxOcc,
            mkCon2TagOcc, mkTag2ConOcc, mkMaxTagOcc,
            mkClassDataConOcc, mkDictOcc, mkIPOcc,
            mkSpecOcc, mkForeignExportOcc, mkRepEqOcc,
            mkGenR, mkGen1R,
            mkDataTOcc, mkDataCOcc, mkDataConWorkerOcc,
            mkSuperDictSelOcc, mkSuperDictAuxOcc,
            mkLocalOcc, mkMethodOcc, mkInstTyTcOcc,
            mkInstTyCoOcc, mkEqPredCoOcc,
            mkRecFldSelOcc,
            mkTyConRepOcc,

            -- ** Deconstruction
            occNameFS, occNameString, occNameSpace,

            isVarOcc, isTvOcc, isTcOcc, isDataOcc, isDataSymOcc, isSymOcc, isValOcc,
            parenSymOcc, startsWithUnderscore,

            isTcClsNameSpace, isTvNameSpace, isDataConNameSpace, isVarNameSpace, isValNameSpace,

            -- * The 'OccEnv' type
            OccEnv, emptyOccEnv, unitOccEnv, extendOccEnv, mapOccEnv,
            lookupOccEnv, mkOccEnv, mkOccEnv_C, extendOccEnvList, elemOccEnv,
            occEnvElts, foldOccEnv, plusOccEnv, plusOccEnv_C, extendOccEnv_C,
            extendOccEnv_Acc, filterOccEnv, delListFromOccEnv, delFromOccEnv,
            alterOccEnv, pprOccEnv,

            -- * The 'OccSet' type
            OccSet, emptyOccSet, unitOccSet, mkOccSet, extendOccSet,
            extendOccSetList,
            unionOccSets, unionManyOccSets, minusOccSet, elemOccSet,
            isEmptyOccSet, intersectOccSet, intersectsOccSet,
            filterOccSet,

            -- * Tidying up
            TidyOccEnv, emptyTidyOccEnv, initTidyOccEnv,
            tidyOccName, avoidClashesOccEnv,

            -- FsEnv
            FastStringEnv, emptyFsEnv, lookupFsEnv, extendFsEnv, mkFsEnv
        ) where

    import GhcPrelude

    import Util
    import Unique
    import DynFlags
    import UniqFM
    import UniqSet
    import FastString
    import FastStringEnv
    import Outputable
    import Lexeme
    import Binary
    import Control.DeepSeq
    import Data.Char
    import Data.Data

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Name space}
    *                                                                      *
    ************************************************************************
    -}

    data NameSpace = VarName        -- Variables, including "real" data constructors
                   | DataName       -- "Source" data constructors
                   | TvName         -- Type variables
                   | TcClsName      -- Type constructors and classes; Haskell has them
                                    -- in the same name space for now.
                   deriving( Eq, Ord )

    -- Note [Data Constructors]
    -- see also: Note [Data Constructor Naming] in DataCon.hs
    --
    -- $real_vs_source_data_constructors
    -- There are two forms of data constructor:
    --
    --      [Source data constructors] The data constructors mentioned in Haskell source code
    --
    --      [Real data constructors] The data constructors of the representation type, which may not be the same as the source type
    --
    -- For example:
    --
    -- > data T = T !(Int, Int)
    --
    -- The source datacon has type @(Int, Int) -> T@
    -- The real   datacon has type @Int -> Int -> T@
    --
    -- GHC chooses a representation based on the strictness etc.

    tcName, clsName, tcClsName :: NameSpace
    dataName, srcDataName      :: NameSpace
    tvName, varName            :: NameSpace

    -- Though type constructors and classes are in the same name space now,
    -- the NameSpace type is abstract, so we can easily separate them later
    tcName    = TcClsName           -- Type constructors
    clsName   = TcClsName           -- Classes
    tcClsName = TcClsName           -- Not sure which!

    dataName    = DataName
    srcDataName = DataName  -- Haskell-source data constructors should be
                            -- in the Data name space

    tvName      = TvName
    varName     = VarName

    isDataConNameSpace :: NameSpace -> Bool
    isDataConNameSpace DataName = True
    isDataConNameSpace _        = False

    isTcClsNameSpace :: NameSpace -> Bool
    isTcClsNameSpace TcClsName = True
    isTcClsNameSpace _         = False

    isTvNameSpace :: NameSpace -> Bool
    isTvNameSpace TvName = True
    isTvNameSpace _      = False

    isVarNameSpace :: NameSpace -> Bool     -- Variables or type variables, but not constructors
    isVarNameSpace TvName  = True
    isVarNameSpace VarName = True
    isVarNameSpace _       = False

    isValNameSpace :: NameSpace -> Bool
    isValNameSpace DataName = True
    isValNameSpace VarName  = True
    isValNameSpace _        = False

    pprNameSpace :: NameSpace -> SDoc
    pprNameSpace DataName  = text "data constructor"
    pprNameSpace VarName   = text "variable"
    pprNameSpace TvName    = text "type variable"
    pprNameSpace TcClsName = text "type constructor or class"

    pprNonVarNameSpace :: NameSpace -> SDoc
    pprNonVarNameSpace VarName = empty
    pprNonVarNameSpace ns = pprNameSpace ns

    pprNameSpaceBrief :: NameSpace -> SDoc
    pprNameSpaceBrief DataName  = char 'd'
    pprNameSpaceBrief VarName   = char 'v'
    pprNameSpaceBrief TvName    = text "tv"
    pprNameSpaceBrief TcClsName = text "tc"

    -- demoteNameSpace lowers the NameSpace if possible.  We can not know
    -- in advance, since a TvName can appear in an HsTyVar.
    -- See Note [Demotion] in RnEnv
    demoteNameSpace :: NameSpace -> Maybe NameSpace
    demoteNameSpace VarName = Nothing
    demoteNameSpace DataName = Nothing
    demoteNameSpace TvName = Nothing
    demoteNameSpace TcClsName = Just DataName

    {-
    ************************************************************************
    *                                                                      *
    \subsection[Name-pieces-datatypes]{The @OccName@ datatypes}
    *                                                                      *
    ************************************************************************
    -}

    -- | Occurrence Name
    --
    -- In this context that means:
    -- "classified (i.e. as a type name, value name, etc) but not qualified
    -- and not yet resolved"
    data OccName = OccName
        { occNameSpace  :: !NameSpace
        , occNameFS     :: !FastString
        }

    instance Eq OccName where
        (OccName sp1 s1) == (OccName sp2 s2) = s1 == s2 && sp1 == sp2

    instance Ord OccName where
            -- Compares lexicographically, *not* by Unique of the string
        compare (OccName sp1 s1) (OccName sp2 s2)
            = (s1  `compare` s2) `thenCmp` (sp1 `compare` sp2)

    instance Data OccName where
      -- don't traverse?
      toConstr _   = abstractConstr "OccName"
      gunfold _ _  = error "gunfold"
      dataTypeOf _ = mkNoRepType "OccName"

    instance HasOccName OccName where
      occName = id

    instance NFData OccName where
      rnf x = x `seq` ()

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Printing}
    *                                                                      *
    ************************************************************************
    -}

    instance Outputable OccName where
        ppr = pprOccName

    instance OutputableBndr OccName where
        pprBndr _ = ppr
        pprInfixOcc n = pprInfixVar (isSymOcc n) (ppr n)
        pprPrefixOcc n = pprPrefixVar (isSymOcc n) (ppr n)

    pprOccName :: OccName -> SDoc
    pprOccName (OccName sp occ)
      = getPprStyle $ \ sty ->
        if codeStyle sty
        then ztext (zEncodeFS occ)
        else pp_occ <> pp_debug sty
      where
        pp_debug sty | debugStyle sty = braces (pprNameSpaceBrief sp)
                     | otherwise      = empty

        pp_occ = sdocWithDynFlags $ \dflags ->
                 if gopt Opt_SuppressUniques dflags
                 then text (strip_th_unique (unpackFS occ))
                 else ftext occ

            -- See Note [Suppressing uniques in OccNames]
        strip_th_unique ('[' : c : _) | isAlphaNum c = []
        strip_th_unique (c : cs) = c : strip_th_unique cs
        strip_th_unique []       = []

    {-
    Note [Suppressing uniques in OccNames]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    This is a hack to de-wobblify the OccNames that contain uniques from
    Template Haskell that have been turned into a string in the OccName.
    See Note [Unique OccNames from Template Haskell] in Convert.hs

    ************************************************************************
    *                                                                      *
    \subsection{Construction}
    *                                                                      *
    ************************************************************************
    -}

    mkOccName :: NameSpace -> String -> OccName
    mkOccName occ_sp str = OccName occ_sp (mkFastString str)

    mkOccNameFS :: NameSpace -> FastString -> OccName
    mkOccNameFS occ_sp fs = OccName occ_sp fs

    mkVarOcc :: String -> OccName
    mkVarOcc s = mkOccName varName s

    mkVarOccFS :: FastString -> OccName
    mkVarOccFS fs = mkOccNameFS varName fs

    mkDataOcc :: String -> OccName
    mkDataOcc = mkOccName dataName

    mkDataOccFS :: FastString -> OccName
    mkDataOccFS = mkOccNameFS dataName

    mkTyVarOcc :: String -> OccName
    mkTyVarOcc = mkOccName tvName

    mkTyVarOccFS :: FastString -> OccName
    mkTyVarOccFS fs = mkOccNameFS tvName fs

    mkTcOcc :: String -> OccName
    mkTcOcc = mkOccName tcName

    mkTcOccFS :: FastString -> OccName
    mkTcOccFS = mkOccNameFS tcName

    mkClsOcc :: String -> OccName
    mkClsOcc = mkOccName clsName

    mkClsOccFS :: FastString -> OccName
    mkClsOccFS = mkOccNameFS clsName

    -- demoteOccName lowers the Namespace of OccName.
    -- see Note [Demotion]
    demoteOccName :: OccName -> Maybe OccName
    demoteOccName (OccName space name) = do
      space' <- demoteNameSpace space
      return $ OccName space' name

    -- Name spaces are related if there is a chance to mean the one when one writes
    -- the other, i.e. variables <-> data constructors and type variables <-> type constructors
    nameSpacesRelated :: NameSpace -> NameSpace -> Bool
    nameSpacesRelated ns1 ns2 = ns1 == ns2 || otherNameSpace ns1 == ns2

    otherNameSpace :: NameSpace -> NameSpace
    otherNameSpace VarName = DataName
    otherNameSpace DataName = VarName
    otherNameSpace TvName = TcClsName
    otherNameSpace TcClsName = TvName

    {- | Other names in the compiler add additional information to an OccName.
    This class provides a consistent way to access the underlying OccName. -}
    class HasOccName name where
      occName :: name -> OccName

    {-
    ************************************************************************
    *                                                                      *
                    Environments
    *                                                                      *
    ************************************************************************

    OccEnvs are used mainly for the envts in ModIfaces.

    Note [The Unique of an OccName]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    They are efficient, because FastStrings have unique Int# keys.  We assume
    this key is less than 2^24, and indeed FastStrings are allocated keys
    sequentially starting at 0.

    So we can make a Unique using
            mkUnique ns key  :: Unique
    where 'ns' is a Char representing the name space.  This in turn makes it
    easy to build an OccEnv.
    -}

    instance Uniquable OccName where
          -- See Note [The Unique of an OccName]
      getUnique (OccName VarName   fs) = mkVarOccUnique  fs
      getUnique (OccName DataName  fs) = mkDataOccUnique fs
      getUnique (OccName TvName    fs) = mkTvOccUnique   fs
      getUnique (OccName TcClsName fs) = mkTcOccUnique   fs

    newtype OccEnv a = A (UniqFM a)
      deriving Data

    emptyOccEnv :: OccEnv a
    unitOccEnv  :: OccName -> a -> OccEnv a
    extendOccEnv :: OccEnv a -> OccName -> a -> OccEnv a
    extendOccEnvList :: OccEnv a -> [(OccName, a)] -> OccEnv a
    lookupOccEnv :: OccEnv a -> OccName -> Maybe a
    mkOccEnv     :: [(OccName,a)] -> OccEnv a
    mkOccEnv_C   :: (a -> a -> a) -> [(OccName,a)] -> OccEnv a
    elemOccEnv   :: OccName -> OccEnv a -> Bool
    foldOccEnv   :: (a -> b -> b) -> b -> OccEnv a -> b
    occEnvElts   :: OccEnv a -> [a]
    extendOccEnv_C :: (a->a->a) -> OccEnv a -> OccName -> a -> OccEnv a
    extendOccEnv_Acc :: (a->b->b) -> (a->b) -> OccEnv b -> OccName -> a -> OccEnv b
    plusOccEnv     :: OccEnv a -> OccEnv a -> OccEnv a
    plusOccEnv_C   :: (a->a->a) -> OccEnv a -> OccEnv a -> OccEnv a
    mapOccEnv      :: (a->b) -> OccEnv a -> OccEnv b
    delFromOccEnv      :: OccEnv a -> OccName -> OccEnv a
    delListFromOccEnv :: OccEnv a -> [OccName] -> OccEnv a
    filterOccEnv       :: (elt -> Bool) -> OccEnv elt -> OccEnv elt
    alterOccEnv        :: (Maybe elt -> Maybe elt) -> OccEnv elt -> OccName -> OccEnv elt

    emptyOccEnv      = A emptyUFM
    unitOccEnv x y = A $ unitUFM x y
    extendOccEnv (A x) y z = A $ addToUFM x y z
    extendOccEnvList (A x) l = A $ addListToUFM x l
    lookupOccEnv (A x) y = lookupUFM x y
    mkOccEnv     l    = A $ listToUFM l
    elemOccEnv x (A y)       = elemUFM x y
    foldOccEnv a b (A c)     = foldUFM a b c
    occEnvElts (A x)         = eltsUFM x
    plusOccEnv (A x) (A y)   = A $ plusUFM x y
    plusOccEnv_C f (A x) (A y)       = A $ plusUFM_C f x y
    extendOccEnv_C f (A x) y z   = A $ addToUFM_C f x y z
    extendOccEnv_Acc f g (A x) y z   = A $ addToUFM_Acc f g x y z
    mapOccEnv f (A x)        = A $ mapUFM f x
    mkOccEnv_C comb l = A $ addListToUFM_C comb emptyUFM l
    delFromOccEnv (A x) y    = A $ delFromUFM x y
    delListFromOccEnv (A x) y  = A $ delListFromUFM x y
    filterOccEnv x (A y)       = A $ filterUFM x y
    alterOccEnv fn (A y) k     = A $ alterUFM fn y k

    instance Outputable a => Outputable (OccEnv a) where
        ppr x = pprOccEnv ppr x

    pprOccEnv :: (a -> SDoc) -> OccEnv a -> SDoc
    pprOccEnv ppr_elt (A env) = pprUniqFM ppr_elt env

    type OccSet = UniqSet OccName

    emptyOccSet       :: OccSet
    unitOccSet        :: OccName -> OccSet
    mkOccSet          :: [OccName] -> OccSet
    extendOccSet      :: OccSet -> OccName -> OccSet
    extendOccSetList  :: OccSet -> [OccName] -> OccSet
    unionOccSets      :: OccSet -> OccSet -> OccSet
    unionManyOccSets  :: [OccSet] -> OccSet
    minusOccSet       :: OccSet -> OccSet -> OccSet
    elemOccSet        :: OccName -> OccSet -> Bool
    isEmptyOccSet     :: OccSet -> Bool
    intersectOccSet   :: OccSet -> OccSet -> OccSet
    intersectsOccSet  :: OccSet -> OccSet -> Bool
    filterOccSet      :: (OccName -> Bool) -> OccSet -> OccSet

    emptyOccSet       = emptyUniqSet
    unitOccSet        = unitUniqSet
    mkOccSet          = mkUniqSet
    extendOccSet      = addOneToUniqSet
    extendOccSetList  = addListToUniqSet
    unionOccSets      = unionUniqSets
    unionManyOccSets  = unionManyUniqSets
    minusOccSet       = minusUniqSet
    elemOccSet        = elementOfUniqSet
    isEmptyOccSet     = isEmptyUniqSet
    intersectOccSet   = intersectUniqSets
    intersectsOccSet s1 s2 = not (isEmptyOccSet (s1 `intersectOccSet` s2))
    filterOccSet      = filterUniqSet

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Predicates and taking them apart}
    *                                                                      *
    ************************************************************************
    -}

    occNameString :: OccName -> String
    occNameString (OccName _ s) = unpackFS s

    setOccNameSpace :: NameSpace -> OccName -> OccName
    setOccNameSpace sp (OccName _ occ) = OccName sp occ

    isVarOcc, isTvOcc, isTcOcc, isDataOcc :: OccName -> Bool

    isVarOcc (OccName VarName _) = True
    isVarOcc _                   = False

    isTvOcc (OccName TvName _) = True
    isTvOcc _                  = False

    isTcOcc (OccName TcClsName _) = True
    isTcOcc _                     = False

    -- | /Value/ 'OccNames's are those that are either in
    -- the variable or data constructor namespaces
    isValOcc :: OccName -> Bool
    isValOcc (OccName VarName  _) = True
    isValOcc (OccName DataName _) = True
    isValOcc _                    = False

    isDataOcc (OccName DataName _) = True
    isDataOcc _                    = False

    -- | Test if the 'OccName' is a data constructor that starts with
    -- a symbol (e.g. @:@, or @[]@)
    isDataSymOcc :: OccName -> Bool
    isDataSymOcc (OccName DataName s) = isLexConSym s
    isDataSymOcc _                    = False
    -- Pretty inefficient!

    -- | Test if the 'OccName' is that for any operator (whether
    -- it is a data constructor or variable or whatever)
    isSymOcc :: OccName -> Bool
    isSymOcc (OccName DataName s)  = isLexConSym s
    isSymOcc (OccName TcClsName s) = isLexSym s
    isSymOcc (OccName VarName s)   = isLexSym s
    isSymOcc (OccName TvName s)    = isLexSym s
    -- Pretty inefficient!

    parenSymOcc :: OccName -> SDoc -> SDoc
    -- ^ Wrap parens around an operator
    parenSymOcc occ doc | isSymOcc occ = parens doc
                        | otherwise    = doc

    startsWithUnderscore :: OccName -> Bool
    -- ^ Haskell 98 encourages compilers to suppress warnings about unsed
    -- names in a pattern if they start with @_@: this implements that test
    startsWithUnderscore occ = headFS (occNameFS occ) == '_'

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Making system names}
    *                                                                      *
    ************************************************************************

    Here's our convention for splitting up the interface file name space:

       d...         dictionary identifiers
                    (local variables, so no name-clash worries)

    All of these other OccNames contain a mixture of alphabetic
    and symbolic characters, and hence cannot possibly clash with
    a user-written type or function name

       $f...        Dict-fun identifiers (from inst decls)
       $dmop        Default method for 'op'
       $pnC         n'th superclass selector for class C
       $wf          Worker for function 'f'
       $sf..        Specialised version of f
       D:C          Data constructor for dictionary for class C
       NTCo:T       Coercion connecting newtype T with its representation type
       TFCo:R       Coercion connecting a data family to its representation type R

    In encoded form these appear as Zdfxxx etc

            :...            keywords (export:, letrec: etc.)
    --- I THINK THIS IS WRONG!

    This knowledge is encoded in the following functions.

    @mk_deriv@ generates an @OccName@ from the prefix and a string.
    NB: The string must already be encoded!
    -}

    -- | Build an 'OccName' derived from another 'OccName'.
    --
    -- Note that the pieces of the name are passed in as a @[FastString]@ so that
    -- the whole name can be constructed with a single 'concatFS', minimizing
    -- unnecessary intermediate allocations.
    mk_deriv :: NameSpace
             -> FastString      -- ^ A prefix which distinguishes one sort of
                                -- derived name from another
             -> [FastString]    -- ^ The name we are deriving from in pieces which
                                -- will be concatenated.
             -> OccName
    mk_deriv occ_sp sys_prefix str =
        mkOccNameFS occ_sp (concatFS $ sys_prefix : str)

    isDerivedOccName :: OccName -> Bool
    -- ^ Test for definitions internally generated by GHC.  This predicte
    -- is used to suppress printing of internal definitions in some debug prints
    isDerivedOccName occ =
       case occNameString occ of
         '$':c:_ | isAlphaNum c -> True   -- E.g.  $wfoo
         c:':':_ | isAlphaNum c -> True   -- E.g.  N:blah   newtype coercions
         _other                 -> False

    isDefaultMethodOcc :: OccName -> Bool
    isDefaultMethodOcc occ =
       case occNameString occ of
         '$':'d':'m':_ -> True
         _ -> False

    -- | Is an 'OccName' one of a Typeable @TyCon@ or @Module@ binding?
    -- This is needed as these bindings are renamed differently.
    -- See Note [Grand plan for Typeable] in TcTypeable.
    isTypeableBindOcc :: OccName -> Bool
    isTypeableBindOcc occ =
       case occNameString occ of
         '$':'t':'c':_ -> True  -- mkTyConRepOcc
         '$':'t':'r':_ -> True  -- Module binding
         _ -> False

    mkDataConWrapperOcc, mkWorkerOcc,
            mkMatcherOcc, mkBuilderOcc,
            mkDefaultMethodOcc,
            mkClassDataConOcc, mkDictOcc,
            mkIPOcc, mkSpecOcc, mkForeignExportOcc, mkRepEqOcc,
            mkGenR, mkGen1R,
            mkDataConWorkerOcc, mkNewTyCoOcc,
            mkInstTyCoOcc, mkEqPredCoOcc, mkClassOpAuxOcc,
            mkCon2TagOcc, mkTag2ConOcc, mkMaxTagOcc,
            mkTyConRepOcc
       :: OccName -> OccName

    -- These derived variables have a prefix that no Haskell value could have
    mkDataConWrapperOcc = mk_simple_deriv varName  "$W"
    mkWorkerOcc         = mk_simple_deriv varName  "$w"
    mkMatcherOcc        = mk_simple_deriv varName  "$m"
    mkBuilderOcc        = mk_simple_deriv varName  "$b"
    mkDefaultMethodOcc  = mk_simple_deriv varName  "$dm"
    mkClassOpAuxOcc     = mk_simple_deriv varName  "$c"
    mkDictOcc           = mk_simple_deriv varName  "$d"
    mkIPOcc             = mk_simple_deriv varName  "$i"
    mkSpecOcc           = mk_simple_deriv varName  "$s"
    mkForeignExportOcc  = mk_simple_deriv varName  "$f"
    mkRepEqOcc          = mk_simple_deriv tvName   "$r"   -- In RULES involving Coercible
    mkClassDataConOcc   = mk_simple_deriv dataName "C:"     -- Data con for a class
    mkNewTyCoOcc        = mk_simple_deriv tcName   "N:"   -- Coercion for newtypes
    mkInstTyCoOcc       = mk_simple_deriv tcName   "D:"   -- Coercion for type functions
    mkEqPredCoOcc       = mk_simple_deriv tcName   "$co"

    -- Used in derived instances
    mkCon2TagOcc        = mk_simple_deriv varName  "$con2tag_"
    mkTag2ConOcc        = mk_simple_deriv varName  "$tag2con_"
    mkMaxTagOcc         = mk_simple_deriv varName  "$maxtag_"

    -- TyConRepName stuff; see Note [Grand plan for Typeable] in TcTypeable
    mkTyConRepOcc occ = mk_simple_deriv varName prefix occ
      where
        prefix | isDataOcc occ = "$tc'"
               | otherwise     = "$tc"

    -- Generic deriving mechanism
    mkGenR   = mk_simple_deriv tcName "Rep_"
    mkGen1R  = mk_simple_deriv tcName "Rep1_"

    -- Overloaded record field selectors
    mkRecFldSelOcc :: String -> OccName
    mkRecFldSelOcc s = mk_deriv varName "$sel" [fsLit s]

    mk_simple_deriv :: NameSpace -> FastString -> OccName -> OccName
    mk_simple_deriv sp px occ = mk_deriv sp px [occNameFS occ]

    -- Data constructor workers are made by setting the name space
    -- of the data constructor OccName (which should be a DataName)
    -- to VarName
    mkDataConWorkerOcc datacon_occ = setOccNameSpace varName datacon_occ

    mkSuperDictAuxOcc :: Int -> OccName -> OccName
    mkSuperDictAuxOcc index cls_tc_occ
      = mk_deriv varName "$cp" [fsLit $ show index, occNameFS cls_tc_occ]

    mkSuperDictSelOcc :: Int        -- ^ Index of superclass, e.g. 3
                      -> OccName    -- ^ Class, e.g. @Ord@
                      -> OccName    -- ^ Derived 'Occname', e.g. @$p3Ord@
    mkSuperDictSelOcc index cls_tc_occ
      = mk_deriv varName "$p" [fsLit $ show index, occNameFS cls_tc_occ]

    mkLocalOcc :: Unique            -- ^ Unique to combine with the 'OccName'
               -> OccName           -- ^ Local name, e.g. @sat@
               -> OccName           -- ^ Nice unique version, e.g. @$L23sat@
    mkLocalOcc uniq occ
       = mk_deriv varName "$L" [fsLit $ show uniq, occNameFS occ]
            -- The Unique might print with characters
            -- that need encoding (e.g. 'z'!)

    -- | Derive a name for the representation type constructor of a
    -- @data@\/@newtype@ instance.
    mkInstTyTcOcc :: String                 -- ^ Family name, e.g. @Map@
                  -> OccSet                 -- ^ avoid these Occs
                  -> OccName                -- ^ @R:Map@
    mkInstTyTcOcc str = chooseUniqueOcc tcName ('R' : ':' : str)

    mkDFunOcc :: String             -- ^ Typically the class and type glommed together e.g. @OrdMaybe@.
                                    -- Only used in debug mode, for extra clarity
              -> Bool               -- ^ Is this a hs-boot instance DFun?
              -> OccSet             -- ^ avoid these Occs
              -> OccName            -- ^ E.g. @$f3OrdMaybe@

    -- In hs-boot files we make dict funs like $fx7ClsTy, which get bound to the real
    -- thing when we compile the mother module. Reason: we don't know exactly
    -- what the  mother module will call it.

    mkDFunOcc info_str is_boot set
      = chooseUniqueOcc VarName (prefix ++ info_str) set
      where
        prefix | is_boot   = "$fx"
               | otherwise = "$f"

    mkDataTOcc, mkDataCOcc
      :: OccName            -- ^ TyCon or data con string
      -> OccSet             -- ^ avoid these Occs
      -> OccName            -- ^ E.g. @$f3OrdMaybe@
    -- data T = MkT ... deriving( Data ) needs definitions for
    --      $tT   :: Data.Generics.Basics.DataType
    --      $cMkT :: Data.Generics.Basics.Constr
    mkDataTOcc occ = chooseUniqueOcc VarName ("$t" ++ occNameString occ)
    mkDataCOcc occ = chooseUniqueOcc VarName ("$c" ++ occNameString occ)

    {-
    Sometimes we need to pick an OccName that has not already been used,
    given a set of in-use OccNames.
    -}

    chooseUniqueOcc :: NameSpace -> String -> OccSet -> OccName
    chooseUniqueOcc ns str set = loop (mkOccName ns str) (0::Int)
      where
      loop occ n
       | occ `elemOccSet` set = loop (mkOccName ns (str ++ show n)) (n+1)
       | otherwise            = occ

    {-
    We used to add a '$m' to indicate a method, but that gives rise to bad
    error messages from the type checker when we print the function name or pattern
    of an instance-decl binding.  Why? Because the binding is zapped
    to use the method name in place of the selector name.
    (See TcClassDcl.tcMethodBind)

    The way it is now, -ddump-xx output may look confusing, but
    you can always say -dppr-debug to get the uniques.

    However, we *do* have to zap the first character to be lower case,
    because overloaded constructors (blarg) generate methods too.
    And convert to VarName space

    e.g. a call to constructor MkFoo where
            data (Ord a) => Foo a = MkFoo a

    If this is necessary, we do it by prefixing '$m'.  These
    guys never show up in error messages.  What a hack.
    -}

    mkMethodOcc :: OccName -> OccName
    mkMethodOcc occ@(OccName VarName _) = occ
    mkMethodOcc occ                     = mk_simple_deriv varName "$m" occ

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Tidying them up}
    *                                                                      *
    ************************************************************************

    Before we print chunks of code we like to rename it so that
    we don't have to print lots of silly uniques in it.  But we mustn't
    accidentally introduce name clashes!  So the idea is that we leave the
    OccName alone unless it accidentally clashes with one that is already
    in scope; if so, we tack on '1' at the end and try again, then '2', and
    so on till we find a unique one.

    There's a wrinkle for operators.  Consider '>>='.  We can't use '>>=1'
    because that isn't a single lexeme.  So we encode it to 'lle' and *then*
    tack on the '1', if necessary.

    Note [TidyOccEnv]
    ~~~~~~~~~~~~~~~~~
    type TidyOccEnv = UniqFM Int

    * Domain = The OccName's FastString. These FastStrings are "taken";
               make sure that we don't re-use

    * Int, n = A plausible starting point for new guesses
               There is no guarantee that "FSn" is available;
               you must look that up in the TidyOccEnv.  But
               it's a good place to start looking.

    * When looking for a renaming for "foo2" we strip off the "2" and start
      with "foo".  Otherwise if we tidy twice we get silly names like foo23.

      However, if it started with digits at the end, we always make a name
      with digits at the end, rather than shortening "foo2" to just "foo",
      even if "foo" is unused.  Reasons:
         - Plain "foo" might be used later
         - We use trailing digits to subtly indicate a unification variable
           in typechecker error message; see TypeRep.tidyTyVarBndr

    We have to take care though! Consider a machine-generated module (Trac #10370)
      module Foo where
         a1 = e1
         a2 = e2
         ...
         a2000 = e2000
    Then "a1", "a2" etc are all marked taken.  But now if we come across "a7" again,
    we have to do a linear search to find a free one, "a2001".  That might just be
    acceptable once.  But if we now come across "a8" again, we don't want to repeat
    that search.

    So we use the TidyOccEnv mapping for "a" (not "a7" or "a8") as our base for
    starting the search; and we make sure to update the starting point for "a"
    after we allocate a new one.

    Node [Tidying multiple names at once]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    Consider

        > :t (id,id,id)

    Every id contributes a type variable to the type signature, and all of them are
    "a". If we tidy them one by one, we get

        (id,id,id) :: (a2 -> a2, a1 -> a1, a -> a)

    which is a bit unfortunate, as it unfairly renames only one of them. What we
    would like to see is

        (id,id,id) :: (a3 -> a3, a2 -> a2, a1 -> a1)

    To achieve this, the function avoidClashesOccEnv can be used to prepare the
    TidyEnv, by “blocking” every name that occurs twice in the map. This way, none
    of the "a"s will get the privilege of keeping this name, and all of them will
    get a suitable number by tidyOccName.

    This prepared TidyEnv can then be used with tidyOccName. See tidyTyCoVarBndrs
    for an example where this is used.

    This is #12382.

    -}

    type TidyOccEnv = UniqFM Int    -- The in-scope OccNames
      -- See Note [TidyOccEnv]

    emptyTidyOccEnv :: TidyOccEnv
    emptyTidyOccEnv = emptyUFM

    initTidyOccEnv :: [OccName] -> TidyOccEnv       -- Initialise with names to avoid!
    initTidyOccEnv = foldl' add emptyUFM
      where
        add env (OccName _ fs) = addToUFM env fs 1

    -- see Note [Tidying multiple names at once]
    avoidClashesOccEnv :: TidyOccEnv -> [OccName] -> TidyOccEnv
    avoidClashesOccEnv env occs = go env emptyUFM occs
      where
        go env _        [] = env
        go env seenOnce ((OccName _ fs):occs)
          | fs `elemUFM` env      = go env seenOnce                  occs
          | fs `elemUFM` seenOnce = go (addToUFM env fs 1) seenOnce  occs
          | otherwise             = go env (addToUFM seenOnce fs ()) occs

    tidyOccName :: TidyOccEnv -> OccName -> (TidyOccEnv, OccName)
    tidyOccName env occ@(OccName occ_sp fs)
      | not (fs `elemUFM` env)
      = -- Desired OccName is free, so use it,
        -- and record in 'env' that it's no longer available
        (addToUFM env fs 1, occ)

      | otherwise
      = case lookupUFM env base1 of
           Nothing -> (addToUFM env base1 2, OccName occ_sp base1)
           Just n  -> find 1 n
      where
        base :: String  -- Drop trailing digits (see Note [TidyOccEnv])
        base  = dropWhileEndLE isDigit (unpackFS fs)
        base1 = mkFastString (base ++ "1")

        find !k !n
          = case lookupUFM env new_fs of
              Just {} -> find (k+1 :: Int) (n+k)
                           -- By using n+k, the n argument to find goes
                           --    1, add 1, add 2, add 3, etc which
                           -- moves at quadratic speed through a dense patch

              Nothing -> (new_env, OccName occ_sp new_fs)
           where
             new_fs = mkFastString (base ++ show n)
             new_env = addToUFM (addToUFM env new_fs 1) base1 (n+1)
                         -- Update:  base1,  so that next time we'll start where we left off
                         --          new_fs, so that we know it is taken
                         -- If they are the same (n==1), the former wins
                         -- See Note [TidyOccEnv]

    {-
    ************************************************************************
    *                                                                      *
                    Binary instance
        Here rather than BinIface because OccName is abstract
    *                                                                      *
    ************************************************************************
    -}

    instance Binary NameSpace where
        put_ bh VarName = do
                putByte bh 0
        put_ bh DataName = do
                putByte bh 1
        put_ bh TvName = do
                putByte bh 2
        put_ bh TcClsName = do
                putByte bh 3
        get bh = do
                h <- getByte bh
                case h of
                  0 -> do return VarName
                  1 -> do return DataName
                  2 -> do return TvName
                  _ -> do return TcClsName

    instance Binary OccName where
        put_ bh (OccName aa ab) = do
                put_ bh aa
                put_ bh ab
        get bh = do
              aa <- get bh
              ab <- get bh
              return (OccName aa ab)