prelude/TysWiredIn.hs

    {-
    (c) The GRASP Project, Glasgow University, 1994-1998

    \section[TysWiredIn]{Wired-in knowledge about {\em non-primitive} types}
    -}

    {-# LANGUAGE CPP #-}

    -- | This module is about types that can be defined in Haskell, but which
    --   must be wired into the compiler nonetheless.  C.f module TysPrim
    module TysWiredIn (
            -- * All wired in things
            wiredInTyCons, isBuiltInOcc_maybe,

            -- * Bool
            boolTy, boolTyCon, boolTyCon_RDR, boolTyConName,
            trueDataCon,  trueDataConId,  true_RDR,
            falseDataCon, falseDataConId, false_RDR,
            promotedFalseDataCon, promotedTrueDataCon,

            -- * Ordering
            orderingTyCon,
            ltDataCon, ltDataConId,
            eqDataCon, eqDataConId,
            gtDataCon, gtDataConId,
            promotedLTDataCon, promotedEQDataCon, promotedGTDataCon,

            -- * Char
            charTyCon, charDataCon, charTyCon_RDR,
            charTy, stringTy, charTyConName,

            -- * Double
            doubleTyCon, doubleDataCon, doubleTy, doubleTyConName,

            -- * Float
            floatTyCon, floatDataCon, floatTy, floatTyConName,

            -- * Int
            intTyCon, intDataCon, intTyCon_RDR, intDataCon_RDR, intTyConName,
            intTy,

            -- * Word
            wordTyCon, wordDataCon, wordTyConName, wordTy,

            -- * Word8
            word8TyCon, word8DataCon, word8TyConName, word8Ty,

            -- * List
            listTyCon, listTyCon_RDR, listTyConName, listTyConKey,
            nilDataCon, nilDataConName, nilDataConKey,
            consDataCon_RDR, consDataCon, consDataConName,
            promotedNilDataCon, promotedConsDataCon,

            mkListTy,

            -- * Maybe
            maybeTyCon, maybeTyConName,
            nothingDataCon, nothingDataConName, promotedNothingDataCon,
            justDataCon, justDataConName, promotedJustDataCon,

            -- * Tuples
            mkTupleTy, mkBoxedTupleTy,
            tupleTyCon, tupleDataCon, tupleTyConName,
            promotedTupleDataCon,
            unitTyCon, unitDataCon, unitDataConId, unitTy, unitTyConKey,
            pairTyCon,
            unboxedUnitTyCon, unboxedUnitDataCon,
            cTupleTyConName, cTupleTyConNames, isCTupleTyConName,

            -- * Kinds
            typeNatKindCon, typeNatKind, typeSymbolKindCon, typeSymbolKind,
            isLiftedTypeKindTyConName, liftedTypeKind, constraintKind,
            starKindTyCon, starKindTyConName,
            unicodeStarKindTyCon, unicodeStarKindTyConName,
            liftedTypeKindTyCon, constraintKindTyCon,

            -- * Parallel arrays
            mkPArrTy,
            parrTyCon, parrFakeCon, isPArrTyCon, isPArrFakeCon,
            parrTyCon_RDR, parrTyConName,

            -- * Equality predicates
            heqTyCon, heqClass, heqDataCon,
            coercibleTyCon, coercibleDataCon, coercibleClass,

            mkWiredInTyConName, -- This is used in TcTypeNats to define the
                                -- built-in functions for evaluation.

            mkWiredInIdName,    -- used in MkId

            -- * RuntimeRep and friends
            runtimeRepTyCon, vecCountTyCon, vecElemTyCon,

            runtimeRepTy, ptrRepLiftedTy,

            vecRepDataConTyCon, ptrRepUnliftedDataConTyCon,

            voidRepDataConTy, intRepDataConTy,
            wordRepDataConTy, int64RepDataConTy, word64RepDataConTy, addrRepDataConTy,
            floatRepDataConTy, doubleRepDataConTy, unboxedTupleRepDataConTy,

            vec2DataConTy, vec4DataConTy, vec8DataConTy, vec16DataConTy, vec32DataConTy,
            vec64DataConTy,

            int8ElemRepDataConTy, int16ElemRepDataConTy, int32ElemRepDataConTy,
            int64ElemRepDataConTy, word8ElemRepDataConTy, word16ElemRepDataConTy,
            word32ElemRepDataConTy, word64ElemRepDataConTy, floatElemRepDataConTy,
            doubleElemRepDataConTy

        ) where

    #include "HsVersions.h"
    #include "MachDeps.h"

    import {-# SOURCE #-} MkId( mkDataConWorkId, mkDictSelId )

    -- friends:
    import PrelNames
    import TysPrim

    -- others:
    import CoAxiom
    import Id
    import Constants        ( mAX_TUPLE_SIZE, mAX_CTUPLE_SIZE )
    import Module           ( Module )
    import Type
    import DataCon
    import {-# SOURCE #-} ConLike
    import TyCon
    import Class            ( Class, mkClass )
    import RdrName
    import Name
    import NameSet          ( NameSet, mkNameSet, elemNameSet )
    import BasicTypes       ( Arity, RecFlag(..), Boxity(..),
                              TupleSort(..) )
    import ForeignCall
    import SrcLoc           ( noSrcSpan )
    import Unique
    import Data.Array
    import FastString
    import Outputable
    import Util
    import BooleanFormula   ( mkAnd )

    alpha_tyvar :: [TyVar]
    alpha_tyvar = [alphaTyVar]

    alpha_ty :: [Type]
    alpha_ty = [alphaTy]

    {-
    Note [Wiring in RuntimeRep]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The RuntimeRep type (and friends) in GHC.Types has a bunch of constructors,
    making it a pain to wire in. To ease the pain somewhat, we use lists of
    the different bits, like Uniques, Names, DataCons. These lists must be
    kept in sync with each other. The rule is this: use the order as declared
    in GHC.Types. All places where such lists exist should contain a reference
    to this Note, so a search for this Note's name should find all the lists.

    ************************************************************************
    *                                                                      *
    \subsection{Wired in type constructors}
    *                                                                      *
    ************************************************************************

    If you change which things are wired in, make sure you change their
    names in PrelNames, so they use wTcQual, wDataQual, etc
    -}

    -- This list is used only to define PrelInfo.wiredInThings. That in turn
    -- is used to initialise the name environment carried around by the renamer.
    -- This means that if we look up the name of a TyCon (or its implicit binders)
    -- that occurs in this list that name will be assigned the wired-in key we
    -- define here.
    --
    -- Because of their infinite nature, this list excludes tuples, Any and implicit
    -- parameter TyCons. Instead, we have a hack in lookupOrigNameCache to deal with
    -- these names.
    --
    -- See also Note [Known-key names]
    wiredInTyCons :: [TyCon]

    wiredInTyCons = [ unitTyCon     -- Not treated like other tuples, because
                                    -- it's defined in GHC.Base, and there's only
                                    -- one of it.  We put it in wiredInTyCons so
                                    -- that it'll pre-populate the name cache, so
                                    -- the special case in lookupOrigNameCache
                                    -- doesn't need to look out for it
                  , boolTyCon
                  , charTyCon
                  , doubleTyCon
                  , floatTyCon
                  , intTyCon
                  , wordTyCon
                  , word8TyCon
                  , listTyCon
                  , maybeTyCon
                  , parrTyCon
                  , heqTyCon
                  , coercibleTyCon
                  , typeNatKindCon
                  , typeSymbolKindCon
                  , runtimeRepTyCon
                  , vecCountTyCon
                  , vecElemTyCon
                  , constraintKindTyCon
                  , liftedTypeKindTyCon
                  , starKindTyCon
                  , unicodeStarKindTyCon
                  ]

    mkWiredInTyConName :: BuiltInSyntax -> Module -> FastString -> Unique -> TyCon -> Name
    mkWiredInTyConName built_in modu fs unique tycon
      = mkWiredInName modu (mkTcOccFS fs) unique
                      (ATyCon tycon)        -- Relevant TyCon
                      built_in

    mkWiredInDataConName :: BuiltInSyntax -> Module -> FastString -> Unique -> DataCon -> Name
    mkWiredInDataConName built_in modu fs unique datacon
      = mkWiredInName modu (mkDataOccFS fs) unique
                      (AConLike (RealDataCon datacon))    -- Relevant DataCon
                      built_in

    mkWiredInIdName :: Module -> FastString -> Unique -> Id -> Name
    mkWiredInIdName mod fs uniq id
     = mkWiredInName mod (mkOccNameFS Name.varName fs) uniq (AnId id) UserSyntax

    -- See Note [Kind-changing of (~) and Coercible]
    -- in libraries/ghc-prim/GHC/Types.hs
    heqTyConName, heqDataConName, heqSCSelIdName :: Name
    heqTyConName   = mkWiredInTyConName   UserSyntax gHC_TYPES (fsLit "~~")   heqTyConKey      heqTyCon
    heqDataConName = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "Eq#")  heqDataConKey heqDataCon
    heqSCSelIdName = mkWiredInIdName gHC_TYPES (fsLit "HEq_sc") heqSCSelIdKey heqSCSelId

    -- See Note [Kind-changing of (~) and Coercible] in libraries/ghc-prim/GHC/Types.hs
    coercibleTyConName, coercibleDataConName, coercibleSCSelIdName :: Name
    coercibleTyConName   = mkWiredInTyConName   UserSyntax gHC_TYPES (fsLit "Coercible")  coercibleTyConKey   coercibleTyCon
    coercibleDataConName = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "MkCoercible") coercibleDataConKey coercibleDataCon
    coercibleSCSelIdName = mkWiredInIdName gHC_TYPES (fsLit "Coercible_sc") coercibleSCSelIdKey coercibleSCSelId

    charTyConName, charDataConName, intTyConName, intDataConName :: Name
    charTyConName     = mkWiredInTyConName   UserSyntax gHC_TYPES (fsLit "Char") charTyConKey charTyCon
    charDataConName   = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "C#") charDataConKey charDataCon
    intTyConName      = mkWiredInTyConName   UserSyntax gHC_TYPES (fsLit "Int") intTyConKey   intTyCon
    intDataConName    = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "I#") intDataConKey  intDataCon

    boolTyConName, falseDataConName, trueDataConName :: Name
    boolTyConName     = mkWiredInTyConName   UserSyntax gHC_TYPES (fsLit "Bool") boolTyConKey boolTyCon
    falseDataConName  = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "False") falseDataConKey falseDataCon
    trueDataConName   = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "True")  trueDataConKey  trueDataCon

    listTyConName, nilDataConName, consDataConName :: Name
    listTyConName     = mkWiredInTyConName   BuiltInSyntax gHC_TYPES (fsLit "[]") listTyConKey listTyCon
    nilDataConName    = mkWiredInDataConName BuiltInSyntax gHC_TYPES (fsLit "[]") nilDataConKey nilDataCon
    consDataConName   = mkWiredInDataConName BuiltInSyntax gHC_TYPES (fsLit ":") consDataConKey consDataCon

    maybeTyConName, nothingDataConName, justDataConName :: Name
    maybeTyConName     = mkWiredInTyConName   UserSyntax gHC_BASE (fsLit "Maybe")
                                              maybeTyConKey maybeTyCon
    nothingDataConName = mkWiredInDataConName UserSyntax gHC_BASE (fsLit "Nothing")
                                              nothingDataConKey nothingDataCon
    justDataConName    = mkWiredInDataConName UserSyntax gHC_BASE (fsLit "Just")
                                              justDataConKey justDataCon

    wordTyConName, wordDataConName, word8TyConName, word8DataConName :: Name
    wordTyConName      = mkWiredInTyConName   UserSyntax gHC_TYPES (fsLit "Word")   wordTyConKey     wordTyCon
    wordDataConName    = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "W#")     wordDataConKey   wordDataCon
    word8TyConName     = mkWiredInTyConName   UserSyntax gHC_WORD  (fsLit "Word8")  word8TyConKey    word8TyCon
    word8DataConName   = mkWiredInDataConName UserSyntax gHC_WORD  (fsLit "W8#")    word8DataConKey  word8DataCon

    floatTyConName, floatDataConName, doubleTyConName, doubleDataConName :: Name
    floatTyConName     = mkWiredInTyConName   UserSyntax gHC_TYPES (fsLit "Float")  floatTyConKey    floatTyCon
    floatDataConName   = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "F#")     floatDataConKey  floatDataCon
    doubleTyConName    = mkWiredInTyConName   UserSyntax gHC_TYPES (fsLit "Double") doubleTyConKey   doubleTyCon
    doubleDataConName  = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "D#")     doubleDataConKey doubleDataCon

    -- Kinds
    typeNatKindConName, typeSymbolKindConName :: Name
    typeNatKindConName    = mkWiredInTyConName UserSyntax gHC_TYPES (fsLit "Nat")    typeNatKindConNameKey    typeNatKindCon
    typeSymbolKindConName = mkWiredInTyConName UserSyntax gHC_TYPES (fsLit "Symbol") typeSymbolKindConNameKey typeSymbolKindCon

    constraintKindTyConName :: Name
    constraintKindTyConName = mkWiredInTyConName UserSyntax gHC_TYPES (fsLit "Constraint") constraintKindTyConKey   constraintKindTyCon

    liftedTypeKindTyConName, starKindTyConName, unicodeStarKindTyConName
      :: Name
    liftedTypeKindTyConName = mkWiredInTyConName UserSyntax gHC_TYPES (fsLit "Type") liftedTypeKindTyConKey liftedTypeKindTyCon
    starKindTyConName = mkWiredInTyConName UserSyntax gHC_TYPES (fsLit "*") starKindTyConKey starKindTyCon
    unicodeStarKindTyConName = mkWiredInTyConName UserSyntax gHC_TYPES (fsLit "★") unicodeStarKindTyConKey unicodeStarKindTyCon

    runtimeRepTyConName, vecRepDataConName :: Name
    runtimeRepTyConName = mkWiredInTyConName UserSyntax gHC_TYPES (fsLit "RuntimeRep") runtimeRepTyConKey runtimeRepTyCon
    vecRepDataConName = mkWiredInDataConName UserSyntax gHC_TYPES (fsLit "VecRep") vecRepDataConKey vecRepDataCon

    -- See Note [Wiring in RuntimeRep]
    runtimeRepSimpleDataConNames :: [Name]
    runtimeRepSimpleDataConNames
      = zipWith3Lazy mk_special_dc_name
          [ fsLit "PtrRepLifted", fsLit "PtrRepUnlifted"
          , fsLit "VoidRep", fsLit "IntRep"
          , fsLit "WordRep", fsLit "Int64Rep", fsLit "Word64Rep"
          , fsLit "AddrRep", fsLit "FloatRep", fsLit "DoubleRep"
          , fsLit "UnboxedTupleRep" ]
          runtimeRepSimpleDataConKeys
          runtimeRepSimpleDataCons

    vecCountTyConName :: Name
    vecCountTyConName = mkWiredInTyConName UserSyntax gHC_TYPES (fsLit "VecCount") vecCountTyConKey vecCountTyCon

    -- See Note [Wiring in RuntimeRep]
    vecCountDataConNames :: [Name]
    vecCountDataConNames = zipWith3Lazy mk_special_dc_name
                             [ fsLit "Vec2", fsLit "Vec4", fsLit "Vec8"
                             , fsLit "Vec16", fsLit "Vec32", fsLit "Vec64" ]
                             vecCountDataConKeys
                             vecCountDataCons

    vecElemTyConName :: Name
    vecElemTyConName = mkWiredInTyConName UserSyntax gHC_TYPES (fsLit "VecElem") vecElemTyConKey vecElemTyCon

    -- See Note [Wiring in RuntimeRep]
    vecElemDataConNames :: [Name]
    vecElemDataConNames = zipWith3Lazy mk_special_dc_name
                            [ fsLit "Int8ElemRep", fsLit "Int16ElemRep", fsLit "Int32ElemRep"
                            , fsLit "Int64ElemRep", fsLit "Word8ElemRep", fsLit "Word16ElemRep"
                            , fsLit "Word32ElemRep", fsLit "Word64ElemRep"
                            , fsLit "FloatElemRep", fsLit "DoubleElemRep" ]
                            vecElemDataConKeys
                            vecElemDataCons

    mk_special_dc_name :: FastString -> Unique -> DataCon -> Name
    mk_special_dc_name fs u dc = mkWiredInDataConName UserSyntax gHC_TYPES fs u dc

    parrTyConName, parrDataConName :: Name
    parrTyConName   = mkWiredInTyConName   BuiltInSyntax
                        gHC_PARR' (fsLit "[::]") parrTyConKey parrTyCon
    parrDataConName = mkWiredInDataConName UserSyntax
                        gHC_PARR' (fsLit "PArr") parrDataConKey parrDataCon

    boolTyCon_RDR, false_RDR, true_RDR, intTyCon_RDR, charTyCon_RDR,
        intDataCon_RDR, listTyCon_RDR, consDataCon_RDR, parrTyCon_RDR :: RdrName
    boolTyCon_RDR   = nameRdrName boolTyConName
    false_RDR       = nameRdrName falseDataConName
    true_RDR        = nameRdrName trueDataConName
    intTyCon_RDR    = nameRdrName intTyConName
    charTyCon_RDR   = nameRdrName charTyConName
    intDataCon_RDR  = nameRdrName intDataConName
    listTyCon_RDR   = nameRdrName listTyConName
    consDataCon_RDR = nameRdrName consDataConName
    parrTyCon_RDR   = nameRdrName parrTyConName

    {-
    ************************************************************************
    *                                                                      *
    \subsection{mkWiredInTyCon}
    *                                                                      *
    ************************************************************************
    -}

    pcNonRecDataTyCon :: Name -> Maybe CType -> [TyVar] -> [DataCon] -> TyCon
    -- Not an enumeration
    pcNonRecDataTyCon = pcTyCon False NonRecursive

    -- This function assumes that the types it creates have all parameters at
    -- Representational role, and that there is no kind polymorphism.
    pcTyCon :: Bool -> RecFlag -> Name -> Maybe CType -> [TyVar] -> [DataCon] -> TyCon
    pcTyCon is_enum is_rec name cType tyvars cons
      = mkAlgTyCon name
                    (map (mkAnonBinder . tyVarKind) tyvars)
                    liftedTypeKind
                    tyvars
                    (map (const Representational) tyvars)
                    cType
                    []              -- No stupid theta
                    (DataTyCon cons is_enum)
                    (VanillaAlgTyCon (mkPrelTyConRepName name))
                    is_rec
                    False           -- Not in GADT syntax

    pcDataCon :: Name -> [TyVar] -> [Type] -> TyCon -> DataCon
    pcDataCon n univs = pcDataConWithFixity False n univs []  -- no ex_tvs

    pcDataConWithFixity :: Bool      -- ^ declared infix?
                        -> Name      -- ^ datacon name
                        -> [TyVar]   -- ^ univ tyvars
                        -> [TyVar]   -- ^ ex tyvars
                        -> [Type]    -- ^ args
                        -> TyCon
                        -> DataCon
    pcDataConWithFixity infx n = pcDataConWithFixity' infx n (incrUnique (nameUnique n))
                                                      NoRRI
    -- The Name's unique is the first of two free uniques;
    -- the first is used for the datacon itself,
    -- the second is used for the "worker name"
    --
    -- To support this the mkPreludeDataConUnique function "allocates"
    -- one DataCon unique per pair of Ints.

    pcDataConWithFixity' :: Bool -> Name -> Unique -> RuntimeRepInfo
                         -> [TyVar] -> [TyVar]
                         -> [Type] -> TyCon -> DataCon
    -- The Name should be in the DataName name space; it's the name
    -- of the DataCon itself.

    pcDataConWithFixity' declared_infix dc_name wrk_key rri tyvars ex_tyvars arg_tys tycon
      = data_con
      where
        data_con = mkDataCon dc_name declared_infix prom_info
                    (map (const no_bang) arg_tys)
                    []      -- No labelled fields
                    tyvars    (mkNamedBinders Specified tyvars)
                    ex_tyvars (mkNamedBinders Specified ex_tyvars)
                    []      -- No equality spec
                    []      -- No theta
                    arg_tys (mkTyConApp tycon (mkTyVarTys tyvars))
                    rri
                    tycon
                    []      -- No stupid theta
                    (mkDataConWorkId wrk_name data_con)
                    NoDataConRep    -- Wired-in types are too simple to need wrappers

        no_bang = HsSrcBang Nothing NoSrcUnpack NoSrcStrict

        modu     = ASSERT( isExternalName dc_name )
                   nameModule dc_name
        dc_occ   = nameOccName dc_name
        wrk_occ  = mkDataConWorkerOcc dc_occ
        wrk_name = mkWiredInName modu wrk_occ wrk_key
                                 (AnId (dataConWorkId data_con)) UserSyntax

        prom_info = mkPrelTyConRepName dc_name

    -- used for RuntimeRep and friends
    pcSpecialDataCon :: Name -> [Type] -> TyCon -> RuntimeRepInfo -> DataCon
    pcSpecialDataCon dc_name arg_tys tycon rri
      = pcDataConWithFixity' False dc_name (incrUnique (nameUnique dc_name)) rri
                             [] [] arg_tys tycon

    {-
    ************************************************************************
    *                                                                      *
          Kinds
    *                                                                      *
    ************************************************************************
    -}

    typeNatKindCon, typeSymbolKindCon :: TyCon
    -- data Nat
    -- data Symbol
    typeNatKindCon    = pcTyCon False NonRecursive typeNatKindConName    Nothing [] []
    typeSymbolKindCon = pcTyCon False NonRecursive typeSymbolKindConName Nothing [] []

    typeNatKind, typeSymbolKind :: Kind
    typeNatKind    = mkTyConTy typeNatKindCon
    typeSymbolKind = mkTyConTy typeSymbolKindCon

    constraintKindTyCon :: TyCon
    constraintKindTyCon = pcTyCon False NonRecursive constraintKindTyConName
                                  Nothing [] []

    liftedTypeKind, constraintKind :: Kind
    liftedTypeKind   = tYPE ptrRepLiftedTy
    constraintKind   = mkTyConApp constraintKindTyCon []

    {-
    ************************************************************************
    *                                                                      *
                    Stuff for dealing with tuples
    *                                                                      *
    ************************************************************************

    Note [How tuples work]  See also Note [Known-key names] in PrelNames
    ~~~~~~~~~~~~~~~~~~~~~~
    * There are three families of tuple TyCons and corresponding
      DataCons, expressed by the type BasicTypes.TupleSort:
        data TupleSort = BoxedTuple | UnboxedTuple | ConstraintTuple

    * All three families are AlgTyCons, whose AlgTyConRhs is TupleTyCon

    * BoxedTuples
        - A wired-in type
        - Data type declarations in GHC.Tuple
        - The data constructors really have an info table

    * UnboxedTuples
        - A wired-in type
        - Have a pretend DataCon, defined in GHC.Prim,
          but no actual declaration and no info table

    * ConstraintTuples
        - Are known-key rather than wired-in. Reason: it's awkward to
          have all the superclass selectors wired-in.
        - Declared as classes in GHC.Classes, e.g.
             class (c1,c2) => (c1,c2)
        - Given constraints: the superclasses automatically become available
        - Wanted constraints: there is a built-in instance
             instance (c1,c2) => (c1,c2)
        - Currently just go up to 16; beyond that
          you have to use manual nesting
        - Their OccNames look like (%,,,%), so they can easily be
          distinguished from term tuples.  But (following Haskell) we
          pretty-print saturated constraint tuples with round parens; see
          BasicTypes.tupleParens.

    * In quite a lot of places things are restrcted just to
      BoxedTuple/UnboxedTuple, and then we used BasicTypes.Boxity to distinguish
      E.g. tupleTyCon has a Boxity argument

    * When looking up an OccName in the original-name cache
      (IfaceEnv.lookupOrigNameCache), we spot the tuple OccName to make sure
      we get the right wired-in name.  This guy can't tell the difference
      betweeen BoxedTuple and ConstraintTuple (same OccName!), so tuples
      are not serialised into interface files using OccNames at all.

    Note [One-tuples]
    ~~~~~~~~~~~~~~~~~
    GHC supports both boxed and unboxed one-tuples:
     - Unboxed one-tuples are sometimes useful when returning a
       single value after CPR analysis
     - A boxed one-tuple is used by DsUtils.mkSelectorBinds, when
       there is just one binder
    Basically it keeps everythig uniform.

    However the /naming/ of the type/data constructors for one-tuples is a
    bit odd:
      3-tuples:  (,,)   (,,)#
      2-tuples:  (,)    (,)#
      1-tuples:  ??
      0-tuples:  ()     ()#

    Zero-tuples have used up the logical name. So we use 'Unit' and 'Unit#'
    for one-tuples.  So in ghc-prim:GHC.Tuple we see the declarations:
      data ()     = ()
      data Unit a = Unit a
      data (a,b)  = (a,b)

    NB (Feb 16): for /constraint/ one-tuples I have 'Unit%' but no class
    decl in GHC.Classes, so I think this part may not work properly. But
    it's unused I think.
    -}

    isBuiltInOcc_maybe :: OccName -> Maybe Name
    -- Built in syntax isn't "in scope" so these OccNames
    -- map to wired-in Names with BuiltInSyntax
    isBuiltInOcc_maybe occ
      = case occNameString occ of
            "[]"             -> choose_ns listTyConName nilDataConName
            ":"              -> Just consDataConName
            "[::]"           -> Just parrTyConName
            "()"             -> tup_name Boxed      0
            "(##)"           -> tup_name Unboxed    0
            '(':',':rest     -> parse_tuple Boxed   2 rest
            '(':'#':',':rest -> parse_tuple Unboxed 2 rest
            _other           -> Nothing
      where
        ns = occNameSpace occ

        parse_tuple sort n rest
          | (',' : rest2) <- rest   = parse_tuple sort (n+1) rest2
          | tail_matches sort rest  = tup_name sort n
          | otherwise               = Nothing

        tail_matches Boxed   ")" = True
        tail_matches Unboxed "#)" = True
        tail_matches _       _    = False

        tup_name boxity arity
          = choose_ns (getName (tupleTyCon   boxity arity))
                      (getName (tupleDataCon boxity arity))

        choose_ns tc dc
          | isTcClsNameSpace ns   = Just tc
          | isDataConNameSpace ns = Just dc
          | otherwise             = pprPanic "tup_name" (ppr occ)

    mkTupleOcc :: NameSpace -> Boxity -> Arity -> OccName
    -- No need to cache these, the caching is done in mk_tuple
    mkTupleOcc ns Boxed   ar = mkOccName ns (mkBoxedTupleStr   ar)
    mkTupleOcc ns Unboxed ar = mkOccName ns (mkUnboxedTupleStr ar)

    mkCTupleOcc :: NameSpace -> Arity -> OccName
    mkCTupleOcc ns ar = mkOccName ns (mkConstraintTupleStr ar)

    mkBoxedTupleStr :: Arity -> String
    mkBoxedTupleStr 0  = "()"
    mkBoxedTupleStr 1  = "Unit"   -- See Note [One-tuples]
    mkBoxedTupleStr ar = '(' : commas ar ++ ")"

    mkUnboxedTupleStr :: Arity -> String
    mkUnboxedTupleStr 0  = "(##)"
    mkUnboxedTupleStr 1  = "Unit#"  -- See Note [One-tuples]
    mkUnboxedTupleStr ar = "(#" ++ commas ar ++ "#)"

    mkConstraintTupleStr :: Arity -> String
    mkConstraintTupleStr 0  = "(%%)"
    mkConstraintTupleStr 1  = "Unit%"   -- See Note [One-tuples]
    mkConstraintTupleStr ar = "(%" ++ commas ar ++ "%)"

    commas :: Arity -> String
    commas ar = take (ar-1) (repeat ',')

    cTupleTyConName :: Arity -> Name
    cTupleTyConName arity
      = mkExternalName (mkCTupleTyConUnique arity) gHC_CLASSES
                       (mkCTupleOcc tcName arity) noSrcSpan
      -- The corresponding DataCon does not have a known-key name

    cTupleTyConNames :: [Name]
    cTupleTyConNames = map cTupleTyConName (0 : [2..mAX_CTUPLE_SIZE])

    cTupleTyConNameSet :: NameSet
    cTupleTyConNameSet = mkNameSet cTupleTyConNames

    isCTupleTyConName :: Name -> Bool
    -- Use Type.isCTupleClass where possible
    isCTupleTyConName n
     = ASSERT2( isExternalName n, ppr n )
       nameModule n == gHC_CLASSES
       && n `elemNameSet` cTupleTyConNameSet

    tupleTyCon :: Boxity -> Arity -> TyCon
    tupleTyCon sort i | i > mAX_TUPLE_SIZE = fst (mk_tuple sort i)  -- Build one specially
    tupleTyCon Boxed   i = fst (boxedTupleArr   ! i)
    tupleTyCon Unboxed i = fst (unboxedTupleArr ! i)

    tupleTyConName :: TupleSort -> Arity -> Name
    tupleTyConName ConstraintTuple a = cTupleTyConName a
    tupleTyConName BoxedTuple      a = tyConName (tupleTyCon Boxed a)
    tupleTyConName UnboxedTuple    a = tyConName (tupleTyCon Unboxed a)

    promotedTupleDataCon :: Boxity -> Arity -> TyCon
    promotedTupleDataCon boxity i = promoteDataCon (tupleDataCon boxity i)

    tupleDataCon :: Boxity -> Arity -> DataCon
    tupleDataCon sort i | i > mAX_TUPLE_SIZE = snd (mk_tuple sort i)    -- Build one specially
    tupleDataCon Boxed   i = snd (boxedTupleArr   ! i)
    tupleDataCon Unboxed i = snd (unboxedTupleArr ! i)

    boxedTupleArr, unboxedTupleArr :: Array Int (TyCon,DataCon)
    boxedTupleArr   = listArray (0,mAX_TUPLE_SIZE) [mk_tuple Boxed   i | i <- [0..mAX_TUPLE_SIZE]]
    unboxedTupleArr = listArray (0,mAX_TUPLE_SIZE) [mk_tuple Unboxed i | i <- [0..mAX_TUPLE_SIZE]]

    mk_tuple :: Boxity -> Int -> (TyCon,DataCon)
    mk_tuple boxity arity = (tycon, tuple_con)
      where
            tycon   = mkTupleTyCon tc_name tc_binders tc_res_kind tc_arity tyvars tuple_con
                                   tup_sort flavour

            (tup_sort, modu, tc_binders, tc_res_kind, tc_arity, tyvars, tyvar_tys, flavour)
              = case boxity of
              Boxed ->
                let boxed_tyvars = take arity alphaTyVars in
                ( BoxedTuple
                , gHC_TUPLE
                , nOfThem arity (mkAnonBinder liftedTypeKind)
                , liftedTypeKind
                , arity
                , boxed_tyvars
                , mkTyVarTys boxed_tyvars
                , VanillaAlgTyCon (mkPrelTyConRepName tc_name)
                )
                -- See Note [Unboxed tuple RuntimeRep vars] in TyCon
              Unboxed ->
                let all_tvs = mkTemplateTyVars (replicate arity runtimeRepTy ++
                                                map (tYPE . mkTyVarTy) (take arity all_tvs))
                       -- NB: This must be one call to mkTemplateTyVars, to make
                       -- sure that all the uniques are different
                    (rr_tvs, open_tvs) = splitAt arity all_tvs
                    res_rep | arity == 0 = voidRepDataConTy
                                  -- See Note [Nullary unboxed tuple] in Type
                            | otherwise  = unboxedTupleRepDataConTy
                in
                ( UnboxedTuple
                , gHC_PRIM
                , mkNamedBinders Specified rr_tvs ++
                  map (mkAnonBinder . tyVarKind) open_tvs
                , tYPE res_rep
                , arity * 2
                , all_tvs
                , mkTyVarTys open_tvs
                , UnboxedAlgTyCon
                )

            tc_name = mkWiredInName modu (mkTupleOcc tcName boxity arity) tc_uniq
                                    (ATyCon tycon) BuiltInSyntax
            tuple_con = pcDataCon dc_name tyvars tyvar_tys tycon
            dc_name   = mkWiredInName modu (mkTupleOcc dataName boxity arity) dc_uniq
                                      (AConLike (RealDataCon tuple_con)) BuiltInSyntax
            tc_uniq   = mkTupleTyConUnique   boxity arity
            dc_uniq   = mkTupleDataConUnique boxity arity

    unitTyCon :: TyCon
    unitTyCon = tupleTyCon Boxed 0

    unitTyConKey :: Unique
    unitTyConKey = getUnique unitTyCon

    unitDataCon :: DataCon
    unitDataCon   = head (tyConDataCons unitTyCon)

    unitDataConId :: Id
    unitDataConId = dataConWorkId unitDataCon

    pairTyCon :: TyCon
    pairTyCon = tupleTyCon Boxed 2

    unboxedUnitTyCon :: TyCon
    unboxedUnitTyCon = tupleTyCon Unboxed 0

    unboxedUnitDataCon :: DataCon
    unboxedUnitDataCon = tupleDataCon   Unboxed 0

    {- *********************************************************************
    *                                                                      *
                  Equality types and classes
    *                                                                      *
    ********************************************************************* -}

    -- See Note [The equality types story] in TysPrim
    -- (:~~: :: forall k1 k2 (a :: k1) (b :: k2). a -> b -> Constraint)
    heqTyCon, coercibleTyCon :: TyCon
    heqClass, coercibleClass :: Class
    heqDataCon, coercibleDataCon :: DataCon
    heqSCSelId, coercibleSCSelId :: Id

    (heqTyCon, heqClass, heqDataCon, heqSCSelId)
      = (tycon, klass, datacon, sc_sel_id)
      where
        tycon     = mkClassTyCon heqTyConName binders tvs roles
                                 rhs klass NonRecursive
                                 (mkPrelTyConRepName heqTyConName)
        klass     = mkClass tvs [] [sc_pred] [sc_sel_id] [] [] (mkAnd []) tycon
        datacon   = pcDataCon heqDataConName tvs [sc_pred] tycon

        binders   = [ mkNamedBinder Specified kv1
                    , mkNamedBinder Specified kv2
                    , mkAnonBinder k1
                    , mkAnonBinder k2 ]
        kv1:kv2:_ = drop 9 alphaTyVars -- gets "j" and "k"
        k1        = mkTyVarTy kv1
        k2        = mkTyVarTy kv2
        [av,bv]   = mkTemplateTyVars [k1, k2]
        tvs       = [kv1, kv2, av, bv]
        roles     = [Nominal, Nominal, Nominal, Nominal]
        rhs       = DataTyCon { data_cons = [datacon], is_enum = False }

        sc_pred   = mkTyConApp eqPrimTyCon (mkTyVarTys tvs)
        sc_sel_id = mkDictSelId heqSCSelIdName klass

    (coercibleTyCon, coercibleClass, coercibleDataCon, coercibleSCSelId)
      = (tycon, klass, datacon, sc_sel_id)
      where
        tycon     = mkClassTyCon coercibleTyConName binders tvs roles
                                 rhs klass NonRecursive
                                 (mkPrelTyConRepName coercibleTyConName)
        klass     = mkClass tvs [] [sc_pred] [sc_sel_id] [] [] (mkAnd []) tycon
        datacon   = pcDataCon coercibleDataConName tvs [sc_pred] tycon

        binders   = [ mkNamedBinder Specified kKiVar
                    , mkAnonBinder k
                    , mkAnonBinder k ]
        k         = mkTyVarTy kKiVar
        [av,bv]   = mkTemplateTyVars [k, k]
        tvs       = [kKiVar, av, bv]
        roles     = [Nominal, Representational, Representational]
        rhs       = DataTyCon { data_cons = [datacon], is_enum = False }

        sc_pred   = mkTyConApp eqReprPrimTyCon [k, k, mkTyVarTy av, mkTyVarTy bv]
        sc_sel_id = mkDictSelId coercibleSCSelIdName klass

    {- *********************************************************************
    *                                                                      *
                    Kinds and RuntimeRep
    *                                                                      *
    ********************************************************************* -}

    -- For information about the usage of the following type, see Note [TYPE]
    -- in module TysPrim
    runtimeRepTy :: Type
    runtimeRepTy = mkTyConTy runtimeRepTyCon

    liftedTypeKindTyCon, starKindTyCon, unicodeStarKindTyCon :: TyCon

       -- See Note [TYPE] in TysPrim
    liftedTypeKindTyCon   = mkSynonymTyCon liftedTypeKindTyConName
                                           [] liftedTypeKind
                                           [] []
                                           (tYPE ptrRepLiftedTy)

    starKindTyCon         = mkSynonymTyCon starKindTyConName
                                           [] liftedTypeKind
                                           [] []
                                           (tYPE ptrRepLiftedTy)

    unicodeStarKindTyCon  = mkSynonymTyCon unicodeStarKindTyConName
                                           [] liftedTypeKind
                                           [] []
                                           (tYPE ptrRepLiftedTy)

    runtimeRepTyCon :: TyCon
    runtimeRepTyCon = pcNonRecDataTyCon runtimeRepTyConName Nothing []
                              (vecRepDataCon : runtimeRepSimpleDataCons)

    vecRepDataCon :: DataCon
    vecRepDataCon = pcSpecialDataCon vecRepDataConName [ mkTyConTy vecCountTyCon
                                                       , mkTyConTy vecElemTyCon ]
                                     runtimeRepTyCon
                                     (RuntimeRep prim_rep_fun)
      where
        prim_rep_fun [count, elem]
          | VecCount n <- tyConRuntimeRepInfo (tyConAppTyCon count)
          , VecElem  e <- tyConRuntimeRepInfo (tyConAppTyCon elem)
          = VecRep n e
        prim_rep_fun args
          = pprPanic "vecRepDataCon" (ppr args)

    vecRepDataConTyCon :: TyCon
    vecRepDataConTyCon = promoteDataCon vecRepDataCon

    ptrRepUnliftedDataConTyCon :: TyCon
    ptrRepUnliftedDataConTyCon = promoteDataCon ptrRepUnliftedDataCon

    -- See Note [Wiring in RuntimeRep]
    runtimeRepSimpleDataCons :: [DataCon]
    ptrRepLiftedDataCon, ptrRepUnliftedDataCon :: DataCon
    runtimeRepSimpleDataCons@(ptrRepLiftedDataCon : ptrRepUnliftedDataCon : _)
      = zipWithLazy mk_runtime_rep_dc
        [ PtrRep, PtrRep, VoidRep, IntRep, WordRep, Int64Rep
        , Word64Rep, AddrRep, FloatRep, DoubleRep
        , panic "unboxed tuple PrimRep" ]
        runtimeRepSimpleDataConNames
      where
        mk_runtime_rep_dc primrep name
          = pcSpecialDataCon name [] runtimeRepTyCon (RuntimeRep (\_ -> primrep))

    -- See Note [Wiring in RuntimeRep]
    voidRepDataConTy, intRepDataConTy, wordRepDataConTy, int64RepDataConTy,
      word64RepDataConTy, addrRepDataConTy, floatRepDataConTy, doubleRepDataConTy,
      unboxedTupleRepDataConTy :: Type
    [_, _, voidRepDataConTy, intRepDataConTy, wordRepDataConTy, int64RepDataConTy,
       word64RepDataConTy, addrRepDataConTy, floatRepDataConTy, doubleRepDataConTy,
       unboxedTupleRepDataConTy] = map (mkTyConTy . promoteDataCon)
                                       runtimeRepSimpleDataCons

    vecCountTyCon :: TyCon
    vecCountTyCon = pcNonRecDataTyCon vecCountTyConName Nothing []
                            vecCountDataCons

    -- See Note [Wiring in RuntimeRep]
    vecCountDataCons :: [DataCon]
    vecCountDataCons = zipWithLazy mk_vec_count_dc
                         [ 2, 4, 8, 16, 32, 64 ]
                         vecCountDataConNames
      where
        mk_vec_count_dc n name
          = pcSpecialDataCon name [] vecCountTyCon (VecCount n)

    -- See Note [Wiring in RuntimeRep]
    vec2DataConTy, vec4DataConTy, vec8DataConTy, vec16DataConTy, vec32DataConTy,
      vec64DataConTy :: Type
    [vec2DataConTy, vec4DataConTy, vec8DataConTy, vec16DataConTy, vec32DataConTy,
      vec64DataConTy] = map (mkTyConTy . promoteDataCon) vecCountDataCons

    vecElemTyCon :: TyCon
    vecElemTyCon = pcNonRecDataTyCon vecElemTyConName Nothing [] vecElemDataCons

    -- See Note [Wiring in RuntimeRep]
    vecElemDataCons :: [DataCon]
    vecElemDataCons = zipWithLazy mk_vec_elem_dc
                        [ Int8ElemRep, Int16ElemRep, Int32ElemRep, Int64ElemRep
                        , Word8ElemRep, Word16ElemRep, Word32ElemRep, Word64ElemRep
                        , FloatElemRep, DoubleElemRep ]
                        vecElemDataConNames
      where
        mk_vec_elem_dc elem name
          = pcSpecialDataCon name [] vecElemTyCon (VecElem elem)

    -- See Note [Wiring in RuntimeRep]
    int8ElemRepDataConTy, int16ElemRepDataConTy, int32ElemRepDataConTy,
      int64ElemRepDataConTy, word8ElemRepDataConTy, word16ElemRepDataConTy,
      word32ElemRepDataConTy, word64ElemRepDataConTy, floatElemRepDataConTy,
      doubleElemRepDataConTy :: Type
    [int8ElemRepDataConTy, int16ElemRepDataConTy, int32ElemRepDataConTy,
      int64ElemRepDataConTy, word8ElemRepDataConTy, word16ElemRepDataConTy,
      word32ElemRepDataConTy, word64ElemRepDataConTy, floatElemRepDataConTy,
      doubleElemRepDataConTy] = map (mkTyConTy . promoteDataCon)
                                    vecElemDataCons

    -- The type ('PtrRepLifted)
    ptrRepLiftedTy :: Type
    ptrRepLiftedTy = mkTyConTy $ promoteDataCon ptrRepLiftedDataCon

    {- *********************************************************************
    *                                                                      *
         The boxed primitive types: Char, Int, etc
    *                                                                      *
    ********************************************************************* -}

    charTy :: Type
    charTy = mkTyConTy charTyCon

    charTyCon :: TyCon
    charTyCon   = pcNonRecDataTyCon charTyConName
                           (Just (CType "" Nothing ("HsChar",fsLit "HsChar")))
                           [] [charDataCon]
    charDataCon :: DataCon
    charDataCon = pcDataCon charDataConName [] [charPrimTy] charTyCon

    stringTy :: Type
    stringTy = mkListTy charTy -- convenience only

    intTy :: Type
    intTy = mkTyConTy intTyCon

    intTyCon :: TyCon
    intTyCon = pcNonRecDataTyCon intTyConName
                                (Just (CType "" Nothing ("HsInt",fsLit "HsInt"))) []
                                [intDataCon]
    intDataCon :: DataCon
    intDataCon = pcDataCon intDataConName [] [intPrimTy] intTyCon

    wordTy :: Type
    wordTy = mkTyConTy wordTyCon

    wordTyCon :: TyCon
    wordTyCon = pcNonRecDataTyCon wordTyConName
                          (Just (CType "" Nothing ("HsWord", fsLit "HsWord"))) []
                          [wordDataCon]
    wordDataCon :: DataCon
    wordDataCon = pcDataCon wordDataConName [] [wordPrimTy] wordTyCon

    word8Ty :: Type
    word8Ty = mkTyConTy word8TyCon

    word8TyCon :: TyCon
    word8TyCon = pcNonRecDataTyCon word8TyConName
                          (Just (CType "" Nothing ("HsWord8", fsLit "HsWord8"))) []
                          [word8DataCon]
    word8DataCon :: DataCon
    word8DataCon = pcDataCon word8DataConName [] [wordPrimTy] word8TyCon

    floatTy :: Type
    floatTy = mkTyConTy floatTyCon

    floatTyCon :: TyCon
    floatTyCon   = pcNonRecDataTyCon floatTyConName
                          (Just (CType "" Nothing ("HsFloat", fsLit "HsFloat"))) []
                          [floatDataCon]
    floatDataCon :: DataCon
    floatDataCon = pcDataCon         floatDataConName [] [floatPrimTy] floatTyCon

    doubleTy :: Type
    doubleTy = mkTyConTy doubleTyCon

    doubleTyCon :: TyCon
    doubleTyCon = pcNonRecDataTyCon doubleTyConName
                          (Just (CType "" Nothing ("HsDouble",fsLit "HsDouble"))) []
                          [doubleDataCon]

    doubleDataCon :: DataCon
    doubleDataCon = pcDataCon doubleDataConName [] [doublePrimTy] doubleTyCon

    {-
    ************************************************************************
    *                                                                      *
                  The Bool type
    *                                                                      *
    ************************************************************************

    An ordinary enumeration type, but deeply wired in.  There are no
    magical operations on @Bool@ (just the regular Prelude code).

    {\em BEGIN IDLE SPECULATION BY SIMON}

    This is not the only way to encode @Bool@.  A more obvious coding makes
    @Bool@ just a boxed up version of @Bool#@, like this:
    \begin{verbatim}
    type Bool# = Int#
    data Bool = MkBool Bool#
    \end{verbatim}

    Unfortunately, this doesn't correspond to what the Report says @Bool@
    looks like!  Furthermore, we get slightly less efficient code (I
    think) with this coding. @gtInt@ would look like this:

    \begin{verbatim}
    gtInt :: Int -> Int -> Bool
    gtInt x y = case x of I# x# ->
                case y of I# y# ->
                case (gtIntPrim x# y#) of
                    b# -> MkBool b#
    \end{verbatim}

    Notice that the result of the @gtIntPrim@ comparison has to be turned
    into an integer (here called @b#@), and returned in a @MkBool@ box.

    The @if@ expression would compile to this:
    \begin{verbatim}
    case (gtInt x y) of
      MkBool b# -> case b# of { 1# -> e1; 0# -> e2 }
    \end{verbatim}

    I think this code is a little less efficient than the previous code,
    but I'm not certain.  At all events, corresponding with the Report is
    important.  The interesting thing is that the language is expressive
    enough to describe more than one alternative; and that a type doesn't
    necessarily need to be a straightforwardly boxed version of its
    primitive counterpart.

    {\em END IDLE SPECULATION BY SIMON}
    -}

    boolTy :: Type
    boolTy = mkTyConTy boolTyCon

    boolTyCon :: TyCon
    boolTyCon = pcTyCon True NonRecursive boolTyConName
                        (Just (CType "" Nothing ("HsBool", fsLit "HsBool")))
                        [] [falseDataCon, trueDataCon]

    falseDataCon, trueDataCon :: DataCon
    falseDataCon = pcDataCon falseDataConName [] [] boolTyCon
    trueDataCon  = pcDataCon trueDataConName  [] [] boolTyCon

    falseDataConId, trueDataConId :: Id
    falseDataConId = dataConWorkId falseDataCon
    trueDataConId  = dataConWorkId trueDataCon

    orderingTyCon :: TyCon
    orderingTyCon = pcTyCon True NonRecursive orderingTyConName Nothing
                            [] [ltDataCon, eqDataCon, gtDataCon]

    ltDataCon, eqDataCon, gtDataCon :: DataCon
    ltDataCon = pcDataCon ltDataConName  [] [] orderingTyCon
    eqDataCon = pcDataCon eqDataConName  [] [] orderingTyCon
    gtDataCon = pcDataCon gtDataConName  [] [] orderingTyCon

    ltDataConId, eqDataConId, gtDataConId :: Id
    ltDataConId = dataConWorkId ltDataCon
    eqDataConId = dataConWorkId eqDataCon
    gtDataConId = dataConWorkId gtDataCon

    {-
    ************************************************************************
    *                                                                      *
                The List type
       Special syntax, deeply wired in,
       but otherwise an ordinary algebraic data type
    *                                                                      *
    ************************************************************************

           data [] a = [] | a : (List a)
    -}

    mkListTy :: Type -> Type
    mkListTy ty = mkTyConApp listTyCon [ty]

    listTyCon :: TyCon
    listTyCon = buildAlgTyCon listTyConName alpha_tyvar [Representational]
                              Nothing []
                              (DataTyCon [nilDataCon, consDataCon] False )
                              Recursive False
                              (VanillaAlgTyCon $ mkPrelTyConRepName listTyConName)

    nilDataCon :: DataCon
    nilDataCon  = pcDataCon nilDataConName alpha_tyvar [] listTyCon

    consDataCon :: DataCon
    consDataCon = pcDataConWithFixity True {- Declared infix -}
                   consDataConName
                   alpha_tyvar [] [alphaTy, mkTyConApp listTyCon alpha_ty] listTyCon
    -- Interesting: polymorphic recursion would help here.
    -- We can't use (mkListTy alphaTy) in the defn of consDataCon, else mkListTy
    -- gets the over-specific type (Type -> Type)

    -- Wired-in type Maybe

    maybeTyCon :: TyCon
    maybeTyCon = pcTyCon False NonRecursive maybeTyConName Nothing alpha_tyvar
                         [nothingDataCon, justDataCon]

    nothingDataCon :: DataCon
    nothingDataCon = pcDataCon nothingDataConName alpha_tyvar [] maybeTyCon

    justDataCon :: DataCon
    justDataCon = pcDataCon justDataConName alpha_tyvar [alphaTy] maybeTyCon

    {-
    ** *********************************************************************
    *                                                                      *
                The tuple types
    *                                                                      *
    ************************************************************************

    The tuple types are definitely magic, because they form an infinite
    family.

    \begin{itemize}
    \item
    They have a special family of type constructors, of type @TyCon@
    These contain the tycon arity, but don't require a Unique.

    \item
    They have a special family of constructors, of type
    @Id@. Again these contain their arity but don't need a Unique.

    \item
    There should be a magic way of generating the info tables and
    entry code for all tuples.

    But at the moment we just compile a Haskell source
    file\srcloc{lib/prelude/...} containing declarations like:
    \begin{verbatim}
    data Tuple0             = Tup0
    data Tuple2  a b        = Tup2  a b
    data Tuple3  a b c      = Tup3  a b c
    data Tuple4  a b c d    = Tup4  a b c d
    ...
    \end{verbatim}
    The print-names associated with the magic @Id@s for tuple constructors
    ``just happen'' to be the same as those generated by these
    declarations.

    \item
    The instance environment should have a magic way to know
    that each tuple type is an instances of classes @Eq@, @Ix@, @Ord@ and
    so on. \ToDo{Not implemented yet.}

    \item
    There should also be a way to generate the appropriate code for each
    of these instances, but (like the info tables and entry code) it is
    done by enumeration\srcloc{lib/prelude/InTup?.hs}.
    \end{itemize}
    -}

    -- | Make a tuple type. The list of types should /not/ include any
    -- RuntimeRep specifications.
    mkTupleTy :: Boxity -> [Type] -> Type
    -- Special case for *boxed* 1-tuples, which are represented by the type itself
    mkTupleTy Boxed   [ty] = ty
    mkTupleTy Boxed   tys  = mkTyConApp (tupleTyCon Boxed (length tys)) tys
    mkTupleTy Unboxed tys  = mkTyConApp (tupleTyCon Unboxed (length tys))
                                            (map (getRuntimeRep "mkTupleTy") tys ++ tys)

    -- | Build the type of a small tuple that holds the specified type of thing
    mkBoxedTupleTy :: [Type] -> Type
    mkBoxedTupleTy tys = mkTupleTy Boxed tys

    unitTy :: Type
    unitTy = mkTupleTy Boxed []

    {- *********************************************************************
    *                                                                      *
            The parallel-array type,  [::]
    *                                                                      *
    ************************************************************************

    Special syntax for parallel arrays needs some wired in definitions.
    -}

    -- | Construct a type representing the application of the parallel array constructor
    mkPArrTy    :: Type -> Type
    mkPArrTy ty  = mkTyConApp parrTyCon [ty]

    -- | Represents the type constructor of parallel arrays
    --
    --  * This must match the definition in @PrelPArr@
    --
    -- NB: Although the constructor is given here, it will not be accessible in
    --     user code as it is not in the environment of any compiled module except
    --     @PrelPArr@.
    --
    parrTyCon :: TyCon
    parrTyCon  = pcNonRecDataTyCon parrTyConName Nothing alpha_tyvar [parrDataCon]

    parrDataCon :: DataCon
    parrDataCon  = pcDataCon
                     parrDataConName
                     alpha_tyvar            -- forall'ed type variables
                     [intTy,                -- 1st argument: Int
                      mkTyConApp            -- 2nd argument: Array# a
                        arrayPrimTyCon
                        alpha_ty]
                     parrTyCon

    -- | Check whether a type constructor is the constructor for parallel arrays
    isPArrTyCon    :: TyCon -> Bool
    isPArrTyCon tc  = tyConName tc == parrTyConName

    -- | Fake array constructors
    --
    -- * These constructors are never really used to represent array values;
    --   however, they are very convenient during desugaring (and, in particular,
    --   in the pattern matching compiler) to treat array pattern just like
    --   yet another constructor pattern
    --
    parrFakeCon                        :: Arity -> DataCon
    parrFakeCon i | i > mAX_TUPLE_SIZE  = mkPArrFakeCon  i  -- build one specially
    parrFakeCon i                       = parrFakeConArr!i

    -- pre-defined set of constructors
    --
    parrFakeConArr :: Array Int DataCon
    parrFakeConArr  = array (0, mAX_TUPLE_SIZE) [(i, mkPArrFakeCon i)
                                                | i <- [0..mAX_TUPLE_SIZE]]

    -- build a fake parallel array constructor for the given arity
    --
    mkPArrFakeCon       :: Int -> DataCon
    mkPArrFakeCon arity  = data_con
      where
            data_con  = pcDataCon name [tyvar] tyvarTys parrTyCon
            tyvar     = head alphaTyVars
            tyvarTys  = replicate arity $ mkTyVarTy tyvar
            nameStr   = mkFastString ("MkPArr" ++ show arity)
            name      = mkWiredInName gHC_PARR' (mkDataOccFS nameStr) unique
                                      (AConLike (RealDataCon data_con)) UserSyntax
            unique      = mkPArrDataConUnique arity

    -- | Checks whether a data constructor is a fake constructor for parallel arrays
    isPArrFakeCon      :: DataCon -> Bool
    isPArrFakeCon dcon  = dcon == parrFakeCon (dataConSourceArity dcon)

    -- Promoted Booleans

    promotedFalseDataCon, promotedTrueDataCon :: TyCon
    promotedTrueDataCon   = promoteDataCon trueDataCon
    promotedFalseDataCon  = promoteDataCon falseDataCon

    -- Promoted Maybe
    promotedNothingDataCon, promotedJustDataCon :: TyCon
    promotedNothingDataCon = promoteDataCon nothingDataCon
    promotedJustDataCon    = promoteDataCon justDataCon

    -- Promoted Ordering

    promotedLTDataCon
      , promotedEQDataCon
      , promotedGTDataCon
      :: TyCon
    promotedLTDataCon     = promoteDataCon ltDataCon
    promotedEQDataCon     = promoteDataCon eqDataCon
    promotedGTDataCon     = promoteDataCon gtDataCon

    -- Promoted List
    promotedConsDataCon, promotedNilDataCon :: TyCon
    promotedConsDataCon   = promoteDataCon consDataCon
    promotedNilDataCon    = promoteDataCon nilDataCon