% % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % The @TyCon@ datatype \begin{code}

    module TyCon(
            -- * Main TyCon data types
    	TyCon, FieldLabel,

    	AlgTyConRhs(..), visibleDataCons,
            TyConParent(..), isNoParent,
    	SynTyConRhs(..),
            CoTyConDesc(..),

            -- ** Constructing TyCons
    	mkAlgTyCon,
    	mkClassTyCon,
    	mkFunTyCon,
    	mkPrimTyCon,
    	mkKindTyCon,
    	mkLiftedPrimTyCon,
    	mkTupleTyCon,
    	mkSynTyCon,
            mkSuperKindTyCon,
            mkCoercionTyCon,
            mkForeignTyCon,
            mkAnyTyCon,

            -- ** Predicates on TyCons
            isAlgTyCon,
            isClassTyCon, isFamInstTyCon,
            isFunTyCon,
            isPrimTyCon,
            isTupleTyCon, isUnboxedTupleTyCon, isBoxedTupleTyCon,
            isSynTyCon, isClosedSynTyCon,
            isSuperKindTyCon, isDecomposableTyCon,
            isCoercionTyCon, isCoercionTyCon_maybe,
            isForeignTyCon, isAnyTyCon, tyConHasKind,

    	isInjectiveTyCon,
    	isDataTyCon, isProductTyCon, isEnumerationTyCon,
    	isNewTyCon, isAbstractTyCon,
            isFamilyTyCon, isSynFamilyTyCon, isDataFamilyTyCon,
            isUnLiftedTyCon,
    	isGadtSyntaxTyCon,
    	isTyConAssoc,
    	isRecursiveTyCon,
    	isHiBootTyCon,
            isImplicitTyCon, tyConHasGenerics,

            -- ** Extracting information out of TyCons
    	tyConName,
    	tyConKind,
    	tyConUnique,
    	tyConTyVars,
    	tyConDataCons, tyConDataCons_maybe, tyConSingleDataCon_maybe,
    	tyConFamilySize,
    	tyConStupidTheta,
    	tyConArity,
            tyConParent,
    	tyConClass_maybe,
    	tyConFamInst_maybe, tyConFamilyCoercion_maybe,tyConFamInstSig_maybe,
    	synTyConDefn, synTyConRhs, synTyConType,
    	tyConExtName,		-- External name for foreign types
    	algTyConRhs,
            newTyConRhs, newTyConEtadRhs, unwrapNewTyCon_maybe,
            tupleTyConBoxity,

            -- ** Manipulating TyCons
    	tcExpandTyCon_maybe, coreExpandTyCon_maybe,
    	makeTyConAbstract,
    	newTyConCo_maybe,

            -- * Primitive representations of Types
    	PrimRep(..),
    	tyConPrimRep,
            primRepSizeW
    ) where

    #include "HsVersions.h"

    import {-# SOURCE #-} TypeRep ( Kind, Type, PredType )
    import {-# SOURCE #-} DataCon ( DataCon, isVanillaDataCon )

    import Var
    import Class
    import BasicTypes
    import Name
    import PrelNames
    import Maybes
    import Outputable
    import FastString
    import Constants
    import Util
    import qualified Data.Data as Data

\end{code} ----------------------------------------------- Notes about type families ----------------------------------------------- Note [Type synonym families] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * Type synonym families, also known as "type functions", map directly onto the type functions in FC: type family F a :: * type instance F Int = Bool ..etc... * Reply "yes" to isSynFamilyTyCon, and isFamilyTyCon * From the user's point of view (F Int) and Bool are simply equivalent types. * A Haskell 98 type synonym is a degenerate form of a type synonym family. * Type functions can't appear in the LHS of a type function: type instance F (F Int) = ... -- BAD! * Translation of type family decl: type family F a :: * translates to a SynTyCon 'F', whose SynTyConRhs is SynFamilyTyCon * Translation of type instance decl: type instance F [a] = Maybe a translates to A SynTyCon 'R:FList a', whose SynTyConRhs is (SynonymTyCon (Maybe a)) TyConParent is (FamInstTyCon F [a] co) where co :: F [a] ~ R:FList a Notice that we introduce a gratuitous vanilla type synonym type R:FList a = Maybe a solely so that type and data families can be treated more uniformly, via a single FamInstTyCon descriptor * In the future we might want to support * closed type families (esp when we have proper kinds) * injective type families (allow decomposition) but we don't at the moment [2010] Note [Data type families] ~~~~~~~~~~~~~~~~~~~~~~~~~ See also Note [Wrappers for data instance tycons] in MkId.lhs * Data type families are declared thus data family T a :: * data instance T Int = T1 | T2 Bool Here T is the "family TyCon". * Reply "yes" to isDataFamilyTyCon, and isFamilyTyCon * The user does not see any "equivalent types" as he did with type synonym families. He just sees constructors with types T1 :: T Int T2 :: Bool -> T Int * Here's the FC version of the above declarations: data T a data R:TInt = T1 | T2 Bool axiom ax_ti : T Int ~ R:TInt The R:TInt is the "representation TyCons". It has an AlgTyConParent of FamInstTyCon T [Int] ax_ti * The data contructor T2 has a wrapper (which is what the source-level "T2" invokes): $WT2 :: Bool -> T Int $WT2 b = T2 b `cast` sym ax_ti * A data instance can declare a fully-fledged GADT: data instance T (a,b) where X1 :: T (Int,Bool) X2 :: a -> b -> T (a,b) Here's the FC version of the above declaration: data R:TPair a where X1 :: R:TPair Int Bool X2 :: a -> b -> R:TPair a b axiom ax_pr :: T (a,b) ~ R:TPair a b $WX1 :: forall a b. a -> b -> T (a,b) $WX1 a b (x::a) (y::b) = X2 a b x y `cast` sym (ax_pr a b) The R:TPair are the "representation TyCons". We have a bit of work to do, to unpick the result types of the data instance declaration for T (a,b), to get the result type in the representation; e.g. T (a,b) --> R:TPair a b The representation TyCon R:TList, has an AlgTyConParent of FamInstTyCon T [(a,b)] ax_pr * Notice that T is NOT translated to a FC type function; it just becomes a "data type" with no constructors, which can be coerced inot into R:TInt, R:TPair by the axioms. These axioms axioms come into play when (and *only* when) you - use a data constructor - do pattern matching Rather like newtype, in fact As a result - T behaves just like a data type so far as decomposition is concerned - (T Int) is not implicitly converted to R:TInt during type inference. Indeed the latter type is unknown to the programmer. - There *is* an instance for (T Int) in the type-family instance environment, but it is only used for overlap checking - It's fine to have T in the LHS of a type function: type instance F (T a) = [a] It was this last point that confused me! The big thing is that you should not think of a data family T as a *type function* at all, not even an injective one! We can't allow even injective type functions on the LHS of a type function: type family injective G a :: * type instance F (G Int) = Bool is no good, even if G is injective, because consider type instance G Int = Bool type instance F Bool = Char So a data type family is not an injective type function. It's just a data type with some axioms that connect it to other data types. %************************************************************************ %* * \subsection{The data type} %* * %************************************************************************ \begin{code}

    -- | TyCons represent type constructors. Type constructors are introduced by things such as:
    --
    -- 1) Data declarations: @data Foo = ...@ creates the @Foo@ type constructor of kind @*@
    --
    -- 2) Type synonyms: @type Foo = ...@ creates the @Foo@ type constructor
    --
    -- 3) Newtypes: @newtype Foo a = MkFoo ...@ creates the @Foo@ type constructor of kind @* -> *@
    --
    -- 4) Class declarations: @class Foo where@ creates the @Foo@ type constructor of kind @*@
    --
    -- 5) Type coercions! This is because we represent a coercion from @t1@ to @t2@
    --    as a 'Type', where that type has kind @t1 ~ t2@. See "Coercion" for more on this
    --
    -- This data type also encodes a number of primitive, built in type constructors such as those
    -- for function and tuple types.
    data TyCon
      = -- | The function type constructor, @(->)@
        FunTyCon {
    	tyConUnique :: Unique,
    	tyConName   :: Name,
    	tc_kind   :: Kind,
    	tyConArity  :: Arity
        }

      -- | Algebraic type constructors, which are defined to be those
      -- arising @data@ type and @newtype@ declarations.  All these
      -- constructors are lifted and boxed. See 'AlgTyConRhs' for more
      -- information.
      | AlgTyCon {
    	tyConUnique :: Unique,
    	tyConName   :: Name,
    	tc_kind   :: Kind,
    	tyConArity  :: Arity,

    	tyConTyVars :: [TyVar],	  -- ^ The type variables used in the type constructor.
                                      -- Invariant: length tyvars = arity
    	                          -- Precisely, this list scopes over:
    	                          --
    	                          -- 1. The 'algTcStupidTheta'
    				  -- 2. The cached types in 'algTyConRhs.NewTyCon'
    				  -- 3. The family instance types if present
    				  --
    				  -- Note that it does /not/ scope over the data constructors.

    	algTcGadtSyntax  :: Bool,	-- ^ Was the data type declared with GADT syntax?
    					-- If so, that doesn't mean it's a true GADT;
    					-- only that the "where" form was used.
                                            -- This field is used only to guide pretty-printing

    	algTcStupidTheta :: [PredType],	-- ^ The \"stupid theta\" for the data type
                                            -- (always empty for GADTs).
    	                                -- A \"stupid theta\" is the context to the left
    	                                -- of an algebraic type declaration,
                                            -- e.g. @Eq a@ in the declaration
                                            --    @data Eq a => T a ...@.

    	algTcRhs :: AlgTyConRhs,  -- ^ Contains information about the
                                      -- data constructors of the algebraic type

    	algTcRec :: RecFlag,	  -- ^ Tells us whether the data type is part
                                      -- of a mutually-recursive group or not

    	hasGenerics :: Bool,	  -- ^ Whether generic (in the -XGenerics sense)
                                      -- to\/from functions are available in the exports
                                      -- of the data type's source module.

    	algTcParent :: TyConParent	-- ^ Gives the class or family declaration 'TyCon'
                                            -- for derived 'TyCon's representing class
                                            -- or family instances, respectively.
                                            -- See also 'synTcParent'
        }

      -- | Represents the infinite family of tuple type constructors,
      --   @()@, @(a,b)@, @(# a, b #)@ etc.
      | TupleTyCon {
    	tyConUnique :: Unique,
    	tyConName   :: Name,
    	tc_kind   :: Kind,
    	tyConArity  :: Arity,
    	tyConBoxed  :: Boxity,
    	tyConTyVars :: [TyVar],
    	dataCon     :: DataCon, -- ^ Corresponding tuple data constructor
    	hasGenerics :: Bool
        }

      -- | Represents type synonyms
      | SynTyCon {
    	tyConUnique  :: Unique,
    	tyConName    :: Name,
    	tc_kind    :: Kind,
    	tyConArity   :: Arity,

    	tyConTyVars  :: [TyVar],	-- Bound tyvars

    	synTcRhs     :: SynTyConRhs,	-- ^ Contains information about the
                                            -- expansion of the synonym

            synTcParent  :: TyConParent     -- ^ Gives the family declaration 'TyCon'
                                            -- of 'TyCon's representing family instances

        }

      -- | Primitive types; cannot be defined in Haskell. This includes
      -- the usual suspects (such as @Int#@) as well as foreign-imported
      -- types and kinds
      | PrimTyCon {
    	tyConUnique   :: Unique,
    	tyConName     :: Name,
    	tc_kind       :: Kind,
    	tyConArity    :: Arity,		-- SLPJ Oct06: I'm not sure what the significance
    					--	       of the arity of a primtycon is!

    	primTyConRep  :: PrimRep,	-- ^ Many primitive tycons are unboxed, but some are
                           			--   boxed (represented by pointers). This 'PrimRep'
    			                --   holds that information.
    					-- Only relevant if tc_kind = *

    	isUnLifted   :: Bool,		-- ^ Most primitive tycons are unlifted
                                            --   (may not contain bottom)
    					--   but foreign-imported ones may be lifted

    	tyConExtName :: Maybe FastString   -- ^ @Just e@ for foreign-imported types,
                                               --   holds the name of the imported thing
        }

      -- | Type coercions, such as @(~)@, @sym@, @trans@, @left@ and @right@.
      -- INVARIANT: Coercion TyCons are always fully applied
      -- 		But note that a CoTyCon can be *over*-saturated in a type.
      -- 		E.g.  (sym g1) Int  will be represented as (TyConApp sym [g1,Int])
      | CoTyCon {
    	tyConUnique :: Unique,
            tyConName   :: Name,
    	tyConArity  :: Arity,
    	coTcDesc    :: CoTyConDesc
        }

      -- | Any types.  Like tuples, this is a potentially-infinite family of TyCons
      --   one for each distinct Kind. They have no values at all.
      --   Because there are infinitely many of them (like tuples) they are
      --   defined in GHC.Prim and have names like "Any(*->*)".
      --   Their Unique is derived from the OccName.
      -- See Note [Any types] in TysPrim
      | AnyTyCon {
    	tyConUnique  :: Unique,
    	tyConName    :: Name,
    	tc_kind    :: Kind	-- Never = *; that is done via PrimTyCon
    		     		-- See Note [Any types] in TysPrim
        }

      -- | Super-kinds. These are "kinds-of-kinds" and are never seen in
      -- Haskell source programs.  There are only two super-kinds: TY (aka
      -- "box"), which is the super-kind of kinds that construct types
      -- eventually, and CO (aka "diamond"), which is the super-kind of
      -- kinds that just represent coercions.
      --
      -- Super-kinds have no kind themselves, and have arity zero
      | SuperKindTyCon {
            tyConUnique :: Unique,
            tyConName   :: Name
        }

    -- | Names of the fields in an algebraic record type
    type FieldLabel = Name

    -- | Represents right-hand-sides of 'TyCon's for algebraic types
    data AlgTyConRhs

        -- | Says that we know nothing about this data type, except that
        -- it's represented by a pointer.  Used when we export a data type
        -- abstractly into an .hi file.
      = AbstractTyCon

        -- | Represents an open type family without a fixed right hand
        -- side.  Additional instances can appear at any time.
        --
        -- These are introduced by either a top level declaration:
        --
        -- > data T a :: *
        --
        -- Or an associated data type declaration, within a class declaration:
        --
        -- > class C a b where
        -- >   data T b :: *
      | DataFamilyTyCon

        -- | Information about those 'TyCon's derived from a @data@
        -- declaration. This includes data types with no constructors at
        -- all.
      | DataTyCon {
    	data_cons :: [DataCon],
    			  -- ^ The data type constructors; can be empty if the user
    			  --   declares the type to have no constructors
    			  --
    			  -- INVARIANT: Kept in order of increasing 'DataCon' tag
    			  --	  (see the tag assignment in DataCon.mkDataCon)

    	is_enum :: Bool   -- ^ Cached value: is this an enumeration type?
                              --   See Note [Enumeration types]
        }

      -- | Information about those 'TyCon's derived from a @newtype@ declaration
      | NewTyCon {
    	data_con :: DataCon,	-- ^ The unique constructor for the @newtype@.
                                    --   It has no existentials

    	nt_rhs :: Type,		-- ^ Cached value: the argument type of the constructor,
    	                        -- which is just the representation type of the 'TyCon'
    	                        -- (remember that @newtype@s do not exist at runtime
                                    -- so need a different representation type).
    	                        --
    				-- The free 'TyVar's of this type are the 'tyConTyVars'
                                    -- from the corresponding 'TyCon'

    	nt_etad_rhs :: ([TyVar], Type),
    			-- ^ Same as the 'nt_rhs', but this time eta-reduced.
                            -- Hence the list of 'TyVar's in this field may be
    			-- shorter than the declared arity of the 'TyCon'.

    			-- See Note [Newtype eta]

            nt_co :: Maybe TyCon   -- ^ A 'TyCon' (which is always a 'CoTyCon') that can
                                   -- have a 'Coercion' extracted from it to create
                                   -- the @newtype@ from the representation 'Type'.
                                   --
                                   -- This field is optional for non-recursive @newtype@s only.

    			       -- See Note [Newtype coercions]
    			       -- Invariant: arity = #tvs in nt_etad_rhs;
    			       --	See Note [Newtype eta]
    			       -- Watch out!  If any newtypes become transparent
    			       -- again check Trac #1072.
        }

    -- | Extract those 'DataCon's that we are able to learn about.  Note
    -- that visibility in this sense does not correspond to visibility in
    -- the context of any particular user program!
    visibleDataCons :: AlgTyConRhs -> [DataCon]
    visibleDataCons AbstractTyCon      	      = []
    visibleDataCons DataFamilyTyCon {}		      = []
    visibleDataCons (DataTyCon{ data_cons = cs }) = cs
    visibleDataCons (NewTyCon{ data_con = c })    = [c]

    -- ^ Both type classes as well as family instances imply implicit
    -- type constructors.  These implicit type constructors refer to their parent
    -- structure (ie, the class or family from which they derive) using a type of
    -- the following form.  We use 'TyConParent' for both algebraic and synonym
    -- types, but the variant 'ClassTyCon' will only be used by algebraic 'TyCon's.
    data TyConParent
      = -- | An ordinary type constructor has no parent.
        NoParentTyCon

      -- | Type constructors representing a class dictionary.
      | ClassTyCon
    	Class		-- INVARIANT: the classTyCon of this Class is the current tycon

      -- | An *associated* type of a class.
      | AssocFamilyTyCon
            Class		-- The class in whose declaration the family is declared
                            -- The 'tyConTyVars' of this 'TyCon' may mention some
                            -- of the same type variables as the classTyVars of the
                            -- parent 'Class'.  E.g.
                            --
                            -- @
                            --    class C a b where
                            --      data T c a
                            -- @
                            --
                            -- Here the 'a' is shared with the 'Class', and that is
                            -- important. In an instance declaration we expect the
                            -- two to be instantiated the same way.  Eg.
                            --
                            -- @
                            --    instanc C [x] (Tree y) where
                            --      data T c [x] = T1 x | T2 c
                            -- @

      -- | Type constructors representing an instance of a type family. Parameters:
      --
      --  1) The type family in question
      --
      --  2) Instance types; free variables are the 'tyConTyVars'
      --  of the current 'TyCon' (not the family one). INVARIANT:
      --  the number of types matches the arity of the family 'TyCon'
      --
      --  3) A 'CoTyCon' identifying the representation
      --  type with the type instance family
      | FamInstTyCon	  -- See Note [Data type families]
        			  -- and Note [Type synonym families]
    	TyCon   -- The family TyCon
    	[Type]	-- Argument types (mentions the tyConTyVars of this TyCon)
    	TyCon   -- The coercion constructor

    	-- E.g.  data intance T [a] = ...
    	-- gives a representation tycon:
    	--	data R:TList a = ...
    	-- 	axiom co a :: T [a] ~ R:TList a
    	-- with R:TList's algTcParent = FamInstTyCon T [a] co

    -- | Checks the invariants of a 'TyConParent' given the appropriate type class name, if any
    okParent :: Name -> TyConParent -> Bool
    okParent _       NoParentTyCon                    = True
    okParent tc_name (AssocFamilyTyCon cls)           = tc_name `elem` map tyConName (classATs cls)
    okParent tc_name (ClassTyCon cls)                 = tc_name == tyConName (classTyCon cls)
    okParent _       (FamInstTyCon fam_tc tys _co_tc) = tyConArity fam_tc == length tys

    isNoParent :: TyConParent -> Bool
    isNoParent NoParentTyCon = True
    isNoParent _             = False

    --------------------

    -- | Information pertaining to the expansion of a type synonym (@type@)
    data SynTyConRhs
      = -- | An ordinary type synonyn.
        SynonymTyCon
           Type	      -- This 'Type' is the rhs, and may mention from 'tyConTyVars'.
    		      -- It acts as a template for the expansion when the 'TyCon'
                          -- is applied to some types.

       -- | A type synonym family  e.g. @type family F x y :: * -> *@
       | SynFamilyTyCon

    --------------------
    data CoTyConDesc
      = CoSym   | CoTrans
      | CoLeft  | CoRight
      | CoCsel1 | CoCsel2 | CoCselR
      | CoInst

      | CoAxiom	-- C tvs : F lhs-tys ~ rhs-ty
          { co_ax_tvs :: [TyVar]
          , co_ax_lhs :: Type
          , co_ax_rhs :: Type }

      | CoUnsafe

\end{code} Note [Enumeration types] ~~~~~~~~~~~~~~~~~~~~~~~~ We define datatypes with no constructors to *not* be enumerations; this fixes trac #2578, Otherwise we end up generating an empty table for <mod>_<type>_closure_tbl which is used by tagToEnum# to map Int# to constructors in an enumeration. The empty table apparently upset the linker. Moreover, all the data constructor must be enumerations, meaning they have type (forall abc. T a b c). GADTs are not enumerations. For example consider data T a where T1 :: T Int T2 :: T Bool T3 :: T a What would [T1 ..] be? [T1,T3] :: T Int? Easiest thing is to exclude them. See Trac #4528. Note [Newtype coercions] ~~~~~~~~~~~~~~~~~~~~~~~~ The NewTyCon field nt_co is a a TyCon (a coercion constructor in fact) which is used for coercing from the representation type of the newtype, to the newtype itself. For example, newtype T a = MkT (a -> a) the NewTyCon for T will contain nt_co = CoT where CoT t : T t ~ t -> t. This TyCon is a CoTyCon, so it does not have a kind on its own; it basically has its own typing rule for the fully-applied version. If the newtype T has k type variables then CoT has arity at most k. In the case that the right hand side is a type application ending with the same type variables as the left hand side, we "eta-contract" the coercion. So if we had newtype S a = MkT [a] then we would generate the arity 0 coercion CoS : S ~ []. The primary reason we do this is to make newtype deriving cleaner. In the paper we'd write axiom CoT : (forall t. T t) ~ (forall t. [t]) and then when we used CoT at a particular type, s, we'd say CoT @ s which encodes as (TyConApp instCoercionTyCon [TyConApp CoT [], s]) But in GHC we instead make CoT into a new piece of type syntax, CoTyCon, (like instCoercionTyCon, symCoercionTyCon etc), which must always be saturated, but which encodes as TyConApp CoT [s] In the vocabulary of the paper it's as if we had axiom declarations like axiom CoT t : T t ~ [t] Note [Newtype eta] ~~~~~~~~~~~~~~~~~~ Consider newtype Parser m a = MkParser (Foogle m a) Are these two types equal (to Core)? Monad (Parser m) Monad (Foogle m) Well, yes. But to see that easily we eta-reduce the RHS type of Parser, in this case to ([], Froogle), so that even unsaturated applications of Parser will work right. This eta reduction is done when the type constructor is built, and cached in NewTyCon. The cached field is only used in coreExpandTyCon_maybe. Here's an example that I think showed up in practice Source code: newtype T a = MkT [a] newtype Foo m = MkFoo (forall a. m a -> Int) w1 :: Foo [] w1 = ... w2 :: Foo T w2 = MkFoo (\(MkT x) -> case w1 of MkFoo f -> f x) After desugaring, and discarding the data constructors for the newtypes, we get: w2 :: Foo T w2 = w1 And now Lint complains unless Foo T == Foo [], and that requires T==[] This point carries over to the newtype coercion, because we need to say w2 = w1 `cast` Foo CoT so the coercion tycon CoT must have kind: T ~ [] and arity: 0 %************************************************************************ %* * \subsection{PrimRep} %* * %************************************************************************ A PrimRep is somewhat similar to a CgRep (see codeGen/SMRep) and a MachRep (see cmm/CmmExpr), although each of these types has a distinct and clearly defined purpose: - A PrimRep is a CgRep + information about signedness + information about primitive pointers (AddrRep). Signedness and primitive pointers are required when passing a primitive type to a foreign function, but aren't needed for call/return conventions of Haskell functions. - A MachRep is a basic machine type (non-void, doesn't contain information on pointerhood or signedness, but contains some reps that don't have corresponding Haskell types). \begin{code}

    -- | A 'PrimRep' is an abstraction of a type.  It contains information that
    -- the code generator needs in order to pass arguments, return results,
    -- and store values of this type.
    data PrimRep
      = VoidRep
      | PtrRep
      | IntRep		-- ^ Signed, word-sized value
      | WordRep		-- ^ Unsigned, word-sized value
      | Int64Rep		-- ^ Signed, 64 bit value (with 32-bit words only)
      | Word64Rep		-- ^ Unsigned, 64 bit value (with 32-bit words only)
      | AddrRep		-- ^ A pointer, but /not/ to a Haskell value (use 'PtrRep')
      | FloatRep
      | DoubleRep
      deriving( Eq, Show )

    instance Outputable PrimRep where
      ppr r = text (show r)

    -- | Find the size of a 'PrimRep', in words
    primRepSizeW :: PrimRep -> Int
    primRepSizeW IntRep   = 1
    primRepSizeW WordRep  = 1
    primRepSizeW Int64Rep = wORD64_SIZE `quot` wORD_SIZE
    primRepSizeW Word64Rep= wORD64_SIZE `quot` wORD_SIZE
    primRepSizeW FloatRep = 1    -- NB. might not take a full word
    primRepSizeW DoubleRep= dOUBLE_SIZE `quot` wORD_SIZE
    primRepSizeW AddrRep  = 1
    primRepSizeW PtrRep   = 1
    primRepSizeW VoidRep  = 0

\end{code} %************************************************************************ %* * \subsection{TyCon Construction} %* * %************************************************************************ Note: the TyCon constructors all take a Kind as one argument, even though they could, in principle, work out their Kind from their other arguments. But to do so they need functions from Types, and that makes a nasty module mutual-recursion. And they aren't called from many places. So we compromise, and move their Kind calculation to the call site. \begin{code}

    -- | Given the name of the function type constructor and it's kind, create the
    -- corresponding 'TyCon'. It is reccomended to use 'TypeRep.funTyCon' if you want
    -- this functionality
    mkFunTyCon :: Name -> Kind -> TyCon
    mkFunTyCon name kind
      = FunTyCon {
    	tyConUnique = nameUnique name,
    	tyConName   = name,
    	tc_kind   = kind,
    	tyConArity  = 2
        }

    -- | This is the making of an algebraic 'TyCon'. Notably, you have to
    -- pass in the generic (in the -XGenerics sense) information about the
    -- type constructor - you can get hold of it easily (see Generics
    -- module)
    mkAlgTyCon :: Name
               -> Kind              -- ^ Kind of the resulting 'TyCon'
               -> [TyVar]           -- ^ 'TyVar's scoped over: see 'tyConTyVars'.
                                    --   Arity is inferred from the length of this list
               -> [PredType]        -- ^ Stupid theta: see 'algTcStupidTheta'
               -> AlgTyConRhs       -- ^ Information about dat aconstructors
               -> TyConParent
               -> RecFlag           -- ^ Is the 'TyCon' recursive?
               -> Bool              -- ^ Does it have generic functions? See 'hasGenerics'
               -> Bool              -- ^ Was the 'TyCon' declared with GADT syntax?
               -> TyCon
    mkAlgTyCon name kind tyvars stupid rhs parent is_rec gen_info gadt_syn
      = AlgTyCon {
    	tyConName 	 = name,
    	tyConUnique	 = nameUnique name,
    	tc_kind	         = kind,
    	tyConArity	 = length tyvars,
    	tyConTyVars	 = tyvars,
    	algTcStupidTheta = stupid,
    	algTcRhs         = rhs,
    	algTcParent	 = ASSERT( okParent name parent ) parent,
    	algTcRec	 = is_rec,
    	algTcGadtSyntax  = gadt_syn,
    	hasGenerics      = gen_info
        }

    -- | Simpler specialization of 'mkAlgTyCon' for classes
    mkClassTyCon :: Name -> Kind -> [TyVar] -> AlgTyConRhs -> Class -> RecFlag -> TyCon
    mkClassTyCon name kind tyvars rhs clas is_rec =
      mkAlgTyCon name kind tyvars [] rhs (ClassTyCon clas) is_rec False False

    mkTupleTyCon :: Name
                 -> Kind    -- ^ Kind of the resulting 'TyCon'
                 -> Arity   -- ^ Arity of the tuple
                 -> [TyVar] -- ^ 'TyVar's scoped over: see 'tyConTyVars'
                 -> DataCon
                 -> Boxity  -- ^ Whether the tuple is boxed or unboxed
                 -> Bool    -- ^ Does it have generic functions? See 'hasGenerics'
                 -> TyCon
    mkTupleTyCon name kind arity tyvars con boxed gen_info
      = TupleTyCon {
    	tyConUnique = nameUnique name,
    	tyConName = name,
    	tc_kind = kind,
    	tyConArity = arity,
    	tyConBoxed = boxed,
    	tyConTyVars = tyvars,
    	dataCon = con,
    	hasGenerics = gen_info
        }

    -- ^ Foreign-imported (.NET) type constructors are represented
    -- as primitive, but /lifted/, 'TyCons' for now. They are lifted
    -- because the Haskell type @T@ representing the (foreign) .NET
    -- type @T@ is actually implemented (in ILX) as a @thunk<T>@
    mkForeignTyCon :: Name
                   -> Maybe FastString -- ^ Name of the foreign imported thing, maybe
                   -> Kind
                   -> Arity
                   -> TyCon
    mkForeignTyCon name ext_name kind arity
      = PrimTyCon {
    	tyConName    = name,
    	tyConUnique  = nameUnique name,
    	tc_kind    = kind,
    	tyConArity   = arity,
    	primTyConRep = PtrRep, -- they all do
    	isUnLifted   = False,
    	tyConExtName = ext_name
        }

    -- | Create an unlifted primitive 'TyCon', such as @Int#@
    mkPrimTyCon :: Name  -> Kind -> Arity -> PrimRep -> TyCon
    mkPrimTyCon name kind arity rep
      = mkPrimTyCon' name kind arity rep True

    -- | Kind constructors
    mkKindTyCon :: Name -> Kind -> TyCon
    mkKindTyCon name kind
      = mkPrimTyCon' name kind 0 VoidRep True

    -- | Create a lifted primitive 'TyCon' such as @RealWorld@
    mkLiftedPrimTyCon :: Name  -> Kind -> Arity -> PrimRep -> TyCon
    mkLiftedPrimTyCon name kind arity rep
      = mkPrimTyCon' name kind arity rep False

    mkPrimTyCon' :: Name  -> Kind -> Arity -> PrimRep -> Bool -> TyCon
    mkPrimTyCon' name kind arity rep is_unlifted
      = PrimTyCon {
    	tyConName    = name,
    	tyConUnique  = nameUnique name,
    	tc_kind    = kind,
    	tyConArity   = arity,
    	primTyConRep = rep,
    	isUnLifted   = is_unlifted,
    	tyConExtName = Nothing
        }

    -- | Create a type synonym 'TyCon'
    mkSynTyCon :: Name -> Kind -> [TyVar] -> SynTyConRhs -> TyConParent -> TyCon
    mkSynTyCon name kind tyvars rhs parent
      = SynTyCon {
    	tyConName = name,
    	tyConUnique = nameUnique name,
    	tc_kind = kind,
    	tyConArity = length tyvars,
    	tyConTyVars = tyvars,
    	synTcRhs = rhs,
            synTcParent = parent
        }

    -- | Create a coercion 'TyCon'
    mkCoercionTyCon :: Name -> Arity
                    -> CoTyConDesc
                    -> TyCon
    mkCoercionTyCon name arity desc
      = CoTyCon {
            tyConName   = name,
            tyConUnique = nameUnique name,
            tyConArity  = arity,
            coTcDesc    = desc }

    mkAnyTyCon :: Name -> Kind -> TyCon
    mkAnyTyCon name kind
      = AnyTyCon {  tyConName = name,
    		tc_kind = kind,
            	tyConUnique = nameUnique name }

    -- | Create a super-kind 'TyCon'
    mkSuperKindTyCon :: Name -> TyCon -- Super kinds always have arity zero
    mkSuperKindTyCon name
      = SuperKindTyCon {
            tyConName = name,
            tyConUnique = nameUnique name
      }

\end{code} \begin{code}

    isFunTyCon :: TyCon -> Bool
    isFunTyCon (FunTyCon {}) = True
    isFunTyCon _             = False

    -- | Test if the 'TyCon' is algebraic but abstract (invisible data constructors)
    isAbstractTyCon :: TyCon -> Bool
    isAbstractTyCon (AlgTyCon { algTcRhs = AbstractTyCon }) = True
    isAbstractTyCon _ = False

    -- | Make an algebraic 'TyCon' abstract. Panics if the supplied 'TyCon' is not algebraic
    makeTyConAbstract :: TyCon -> TyCon
    makeTyConAbstract tc@(AlgTyCon {}) = tc { algTcRhs = AbstractTyCon }
    makeTyConAbstract tc = pprPanic "makeTyConAbstract" (ppr tc)

    -- | Does this 'TyCon' represent something that cannot be defined in Haskell?
    isPrimTyCon :: TyCon -> Bool
    isPrimTyCon (PrimTyCon {}) = True
    isPrimTyCon _              = False

    -- | Is this 'TyCon' unlifted (i.e. cannot contain bottom)? Note that this can only
    -- be true for primitive and unboxed-tuple 'TyCon's
    isUnLiftedTyCon :: TyCon -> Bool
    isUnLiftedTyCon (PrimTyCon  {isUnLifted = is_unlifted}) = is_unlifted
    isUnLiftedTyCon (TupleTyCon {tyConBoxed = boxity})      = not (isBoxed boxity)
    isUnLiftedTyCon _    				        = False

    -- | Returns @True@ if the supplied 'TyCon' resulted from either a
    -- @data@ or @newtype@ declaration
    isAlgTyCon :: TyCon -> Bool
    isAlgTyCon (AlgTyCon {})   = True
    isAlgTyCon (TupleTyCon {}) = True
    isAlgTyCon _               = False

    isDataTyCon :: TyCon -> Bool
    -- ^ Returns @True@ for data types that are /definitely/ represented by
    -- heap-allocated constructors.  These are scrutinised by Core-level
    -- @case@ expressions, and they get info tables allocated for them.
    --
    -- Generally, the function will be true for all @data@ types and false
    -- for @newtype@s, unboxed tuples and type family 'TyCon's. But it is
    -- not guarenteed to return @True@ in all cases that it could.
    --
    -- NB: for a data type family, only the /instance/ 'TyCon's
    --     get an info table.  The family declaration 'TyCon' does not
    isDataTyCon (AlgTyCon {algTcRhs = rhs})
      = case rhs of
            DataFamilyTyCon {}  -> False
    	DataTyCon {}  -> True
    	NewTyCon {}   -> False
    	AbstractTyCon -> False	 -- We don't know, so return False
    isDataTyCon (TupleTyCon {tyConBoxed = boxity}) = isBoxed boxity
    isDataTyCon _ = False

    -- | Is this 'TyCon' that for a @newtype@
    isNewTyCon :: TyCon -> Bool
    isNewTyCon (AlgTyCon {algTcRhs = NewTyCon {}}) = True
    isNewTyCon _                                   = False

    -- | Take a 'TyCon' apart into the 'TyVar's it scopes over, the 'Type' it expands
    -- into, and (possibly) a coercion from the representation type to the @newtype@.
    -- Returns @Nothing@ if this is not possible.
    unwrapNewTyCon_maybe :: TyCon -> Maybe ([TyVar], Type, Maybe TyCon)
    unwrapNewTyCon_maybe (AlgTyCon { tyConTyVars = tvs,
    				 algTcRhs = NewTyCon { nt_co = mb_co,
    						       nt_rhs = rhs }})
    			   = Just (tvs, rhs, mb_co)
    unwrapNewTyCon_maybe _     = Nothing

    isProductTyCon :: TyCon -> Bool
    -- | A /product/ 'TyCon' must both:
    --
    -- 1. Have /one/ constructor
    --
    -- 2. /Not/ be existential
    --
    -- However other than this there are few restrictions: they may be @data@ or @newtype@
    -- 'TyCon's of any boxity and may even be recursive.
    isProductTyCon tc@(AlgTyCon {}) = case algTcRhs tc of
    				    DataTyCon{ data_cons = [data_con] }
    						-> isVanillaDataCon data_con
    				    NewTyCon {}	-> True
    				    _           -> False
    isProductTyCon (TupleTyCon {})  = True
    isProductTyCon _                = False

    -- | Is this a 'TyCon' representing a type synonym (@type@)?
    isSynTyCon :: TyCon -> Bool
    isSynTyCon (SynTyCon {}) = True
    isSynTyCon _		 = False

    -- As for newtypes, it is in some contexts important to distinguish between
    -- closed synonyms and synonym families, as synonym families have no unique
    -- right hand side to which a synonym family application can expand.
    --

    isDecomposableTyCon :: TyCon -> Bool
    -- True iff we can decompose (T a b c) into ((T a b) c)
    -- Specifically NOT true of synonyms (open and otherwise) and coercions
    isDecomposableTyCon (SynTyCon {}) = False
    isDecomposableTyCon (CoTyCon {})  = False
    isDecomposableTyCon _other        = True

    -- | Is this an algebraic 'TyCon' declared with the GADT syntax?
    isGadtSyntaxTyCon :: TyCon -> Bool
    isGadtSyntaxTyCon (AlgTyCon { algTcGadtSyntax = res }) = res
    isGadtSyntaxTyCon _                                    = False

    -- | Is this an algebraic 'TyCon' which is just an enumeration of values?
    isEnumerationTyCon :: TyCon -> Bool
    -- See Note [Enumeration types] in TyCon
    isEnumerationTyCon (AlgTyCon {algTcRhs = DataTyCon { is_enum = res }}) = res
    isEnumerationTyCon (TupleTyCon {tyConArity = arity}) = arity == 0
    isEnumerationTyCon _                                                   = False

    -- | Is this a 'TyCon', synonym or otherwise, that may have further instances appear?
    isFamilyTyCon :: TyCon -> Bool
    isFamilyTyCon (SynTyCon {synTcRhs = SynFamilyTyCon {}})  = True
    isFamilyTyCon (AlgTyCon {algTcRhs = DataFamilyTyCon {}}) = True
    isFamilyTyCon _	= False

    -- | Is this a synonym 'TyCon' that can have may have further instances appear?
    isSynFamilyTyCon :: TyCon -> Bool
    isSynFamilyTyCon (SynTyCon {synTcRhs = SynFamilyTyCon {}}) = True
    isSynFamilyTyCon _ = False

    -- | Is this a synonym 'TyCon' that can have may have further instances appear?
    isDataFamilyTyCon :: TyCon -> Bool
    isDataFamilyTyCon (AlgTyCon {algTcRhs = DataFamilyTyCon {}}) = True
    isDataFamilyTyCon _ = False

    -- | Is this a synonym 'TyCon' that can have no further instances appear?
    isClosedSynTyCon :: TyCon -> Bool
    isClosedSynTyCon tycon = isSynTyCon tycon && not (isFamilyTyCon tycon)

    -- | Injective 'TyCon's can be decomposed, so that
    --     T ty1 ~ T ty2  =>  ty1 ~ ty2
    isInjectiveTyCon :: TyCon -> Bool
    isInjectiveTyCon tc = not (isSynTyCon tc)
    	-- Ultimately we may have injective associated types
            -- in which case this test will become more interesting
    	--
    	-- It'd be unusual to call isInjectiveTyCon on a regular H98
    	-- type synonym, because you should probably have expanded it first
    	-- But regardless, it's not injective!

    -- | Are we able to extract informationa 'TyVar' to class argument list
    -- mappping from a given 'TyCon'?
    isTyConAssoc :: TyCon -> Bool
    isTyConAssoc tc = case tyConParent tc of
                         AssocFamilyTyCon {} -> True
                         _                   -> False

    -- The unit tycon didn't used to be classed as a tuple tycon
    -- but I thought that was silly so I've undone it
    -- If it can't be for some reason, it should be a AlgTyCon
    isTupleTyCon :: TyCon -> Bool
    -- ^ Does this 'TyCon' represent a tuple?
    --
    -- NB: when compiling @Data.Tuple@, the tycons won't reply @True@ to
    -- 'isTupleTyCon', becuase they are built as 'AlgTyCons'.  However they
    -- get spat into the interface file as tuple tycons, so I don't think
    -- it matters.
    isTupleTyCon (TupleTyCon {}) = True
    isTupleTyCon _               = False

    -- | Is this the 'TyCon' for an unboxed tuple?
    isUnboxedTupleTyCon :: TyCon -> Bool
    isUnboxedTupleTyCon (TupleTyCon {tyConBoxed = boxity}) = not (isBoxed boxity)
    isUnboxedTupleTyCon _                                  = False

    -- | Is this the 'TyCon' for a boxed tuple?
    isBoxedTupleTyCon :: TyCon -> Bool
    isBoxedTupleTyCon (TupleTyCon {tyConBoxed = boxity}) = isBoxed boxity
    isBoxedTupleTyCon _                                  = False

    -- | Extract the boxity of the given 'TyCon', if it is a 'TupleTyCon'.
    -- Panics otherwise
    tupleTyConBoxity :: TyCon -> Boxity
    tupleTyConBoxity tc = tyConBoxed tc

    -- | Is this a recursive 'TyCon'?
    isRecursiveTyCon :: TyCon -> Bool
    isRecursiveTyCon (AlgTyCon {algTcRec = Recursive}) = True
    isRecursiveTyCon _                                 = False

    -- | Did this 'TyCon' originate from type-checking a .h*-boot file?
    isHiBootTyCon :: TyCon -> Bool
    -- Used for knot-tying in hi-boot files
    isHiBootTyCon (AlgTyCon {algTcRhs = AbstractTyCon}) = True
    isHiBootTyCon _                                     = False

    -- | Is this the 'TyCon' of a foreign-imported type constructor?
    isForeignTyCon :: TyCon -> Bool
    isForeignTyCon (PrimTyCon {tyConExtName = Just _}) = True
    isForeignTyCon _                                   = False

    -- | Is this a super-kind 'TyCon'?
    isSuperKindTyCon :: TyCon -> Bool
    isSuperKindTyCon (SuperKindTyCon {}) = True
    isSuperKindTyCon _                   = False

    -- | Is this an AnyTyCon?
    isAnyTyCon :: TyCon -> Bool
    isAnyTyCon (AnyTyCon {}) = True
    isAnyTyCon _              = False

    -- | Attempt to pull a 'TyCon' apart into the arity and 'coKindFun' of
    -- a coercion 'TyCon'. Returns @Nothing@ if the 'TyCon' is not of the
    -- appropriate kind
    isCoercionTyCon_maybe :: TyCon -> Maybe (Arity, CoTyConDesc)
    isCoercionTyCon_maybe (CoTyCon {tyConArity = ar, coTcDesc = desc})
      = Just (ar, desc)
    isCoercionTyCon_maybe _ = Nothing

    -- | Is this a 'TyCon' that represents a coercion?
    isCoercionTyCon :: TyCon -> Bool
    isCoercionTyCon (CoTyCon {}) = True
    isCoercionTyCon _            = False

    -- | Identifies implicit tycons that, in particular, do not go into interface
    -- files (because they are implicitly reconstructed when the interface is
    -- read).
    --
    -- Note that:
    --
    -- * Associated families are implicit, as they are re-constructed from
    --   the class declaration in which they reside, and
    --
    -- * Family instances are /not/ implicit as they represent the instance body
    --   (similar to a @dfun@ does that for a class instance).
    isImplicitTyCon :: TyCon -> Bool
    isImplicitTyCon tycon | isTyConAssoc tycon           = True
    		      | isSynTyCon tycon	     = False
    		      | isAlgTyCon tycon	     = isClassTyCon tycon ||
    						       isTupleTyCon tycon
    isImplicitTyCon _other                               = True
            -- catches: FunTyCon, PrimTyCon,
            -- CoTyCon, SuperKindTyCon

\end{code} ----------------------------------------------- -- Expand type-constructor applications ----------------------------------------------- \begin{code}

    tcExpandTyCon_maybe, coreExpandTyCon_maybe
    	:: TyCon
    	-> [Type]			-- ^ Arguments to 'TyCon'
    	-> Maybe ([(TyVar,Type)],
    		  Type,
    		  [Type])		-- ^ Returns a 'TyVar' substitution, the body type
                                            -- of the synonym (not yet substituted) and any arguments
                                            -- remaining from the application

    -- ^ Used to create the view the /typechecker/ has on 'TyCon's. We expand (closed) synonyms only, cf. 'coreExpandTyCon_maybe'
    tcExpandTyCon_maybe (SynTyCon {tyConTyVars = tvs,
    			       synTcRhs = SynonymTyCon rhs }) tys
       = expand tvs rhs tys
    tcExpandTyCon_maybe _ _ = Nothing

    ---------------

    -- ^ Used to create the view /Core/ has on 'TyCon's. We expand not only closed synonyms like 'tcExpandTyCon_maybe',
    -- but also non-recursive @newtype@s
    coreExpandTyCon_maybe (AlgTyCon {
             algTcRhs = NewTyCon { nt_etad_rhs = etad_rhs, nt_co = Nothing }}) tys
       = case etad_rhs of	-- Don't do this in the pattern match, lest we accidentally
    			-- match the etad_rhs of a *recursive* newtype
    	(tvs,rhs) -> expand tvs rhs tys

    coreExpandTyCon_maybe tycon tys = tcExpandTyCon_maybe tycon tys

    ----------------
    expand	:: [TyVar] -> Type 			-- Template
    	-> [Type]				-- Args
    	-> Maybe ([(TyVar,Type)], Type, [Type])	-- Expansion
    expand tvs rhs tys
      = case n_tvs `compare` length tys of
    	LT -> Just (tvs `zip` tys, rhs, drop n_tvs tys)
    	EQ -> Just (tvs `zip` tys, rhs, [])
    	GT -> Nothing
       where
         n_tvs = length tvs

\end{code} \begin{code}

    -- | Does this 'TyCon' have any generic to\/from functions available? See also 'hasGenerics'
    tyConHasGenerics :: TyCon -> Bool
    tyConHasGenerics (AlgTyCon {hasGenerics = hg})   = hg
    tyConHasGenerics (TupleTyCon {hasGenerics = hg}) = hg
    tyConHasGenerics _                               = False        -- Synonyms

    tyConKind :: TyCon -> Kind
    tyConKind (FunTyCon   { tc_kind = k }) = k
    tyConKind (AlgTyCon   { tc_kind = k }) = k
    tyConKind (TupleTyCon { tc_kind = k }) = k
    tyConKind (SynTyCon   { tc_kind = k }) = k
    tyConKind (PrimTyCon  { tc_kind = k }) = k
    tyConKind (AnyTyCon   { tc_kind = k }) = k
    tyConKind tc = pprPanic "tyConKind" (ppr tc)	-- SuperKindTyCon and CoTyCon

    tyConHasKind :: TyCon -> Bool
    tyConHasKind (SuperKindTyCon {}) = False
    tyConHasKind (CoTyCon {})        = False
    tyConHasKind _                   = True

    -- | As 'tyConDataCons_maybe', but returns the empty list of constructors if no constructors
    -- could be found
    tyConDataCons :: TyCon -> [DataCon]
    -- It's convenient for tyConDataCons to return the
    -- empty list for type synonyms etc
    tyConDataCons tycon = tyConDataCons_maybe tycon `orElse` []

    -- | Determine the 'DataCon's originating from the given 'TyCon', if the 'TyCon' is the
    -- sort that can have any constructors (note: this does not include abstract algebraic types)
    tyConDataCons_maybe :: TyCon -> Maybe [DataCon]
    tyConDataCons_maybe (AlgTyCon {algTcRhs = DataTyCon { data_cons = cons }}) = Just cons
    tyConDataCons_maybe (AlgTyCon {algTcRhs = NewTyCon { data_con = con }})    = Just [con]
    tyConDataCons_maybe (TupleTyCon {dataCon = con})	       		   = Just [con]
    tyConDataCons_maybe _                                                      = Nothing

    -- | Determine the number of value constructors a 'TyCon' has. Panics if the 'TyCon'
    -- is not algebraic or a tuple
    tyConFamilySize  :: TyCon -> Int
    tyConFamilySize (AlgTyCon   {algTcRhs = DataTyCon {data_cons = cons}}) =
      length cons
    tyConFamilySize (AlgTyCon   {algTcRhs = NewTyCon {}})        = 1
    tyConFamilySize (AlgTyCon   {algTcRhs = DataFamilyTyCon {}}) = 0
    tyConFamilySize (TupleTyCon {})	 		             = 1
    tyConFamilySize other = pprPanic "tyConFamilySize:" (ppr other)

    -- | Extract an 'AlgTyConRhs' with information about data constructors from an algebraic or tuple
    -- 'TyCon'. Panics for any other sort of 'TyCon'
    algTyConRhs :: TyCon -> AlgTyConRhs
    algTyConRhs (AlgTyCon {algTcRhs = rhs}) = rhs
    algTyConRhs (TupleTyCon {dataCon = con, tyConArity = arity})
        = DataTyCon { data_cons = [con], is_enum = arity == 0 }
    algTyConRhs other = pprPanic "algTyConRhs" (ppr other)

\end{code} \begin{code}

    -- | Extract the bound type variables and type expansion of a type synonym 'TyCon'. Panics if the
    -- 'TyCon' is not a synonym
    newTyConRhs :: TyCon -> ([TyVar], Type)
    newTyConRhs (AlgTyCon {tyConTyVars = tvs, algTcRhs = NewTyCon { nt_rhs = rhs }}) = (tvs, rhs)
    newTyConRhs tycon = pprPanic "newTyConRhs" (ppr tycon)

    -- | Extract the bound type variables and type expansion of an eta-contracted type synonym 'TyCon'.
    -- Panics if the 'TyCon' is not a synonym
    newTyConEtadRhs :: TyCon -> ([TyVar], Type)
    newTyConEtadRhs (AlgTyCon {algTcRhs = NewTyCon { nt_etad_rhs = tvs_rhs }}) = tvs_rhs
    newTyConEtadRhs tycon = pprPanic "newTyConEtadRhs" (ppr tycon)

    -- | Extracts the @newtype@ coercion from such a 'TyCon', which can be used to construct something
    -- with the @newtype@s type from its representation type (right hand side). If the supplied 'TyCon'
    -- is not a @newtype@, returns @Nothing@
    newTyConCo_maybe :: TyCon -> Maybe TyCon
    newTyConCo_maybe (AlgTyCon {algTcRhs = NewTyCon { nt_co = co }}) = co
    newTyConCo_maybe _						 = Nothing

    -- | Find the primitive representation of a 'TyCon'
    tyConPrimRep :: TyCon -> PrimRep
    tyConPrimRep (PrimTyCon {primTyConRep = rep}) = rep
    tyConPrimRep tc = ASSERT(not (isUnboxedTupleTyCon tc)) PtrRep

\end{code} \begin{code}

    -- | Find the \"stupid theta\" of the 'TyCon'. A \"stupid theta\" is the context to the left of
    -- an algebraic type declaration, e.g. @Eq a@ in the declaration @data Eq a => T a ...@
    tyConStupidTheta :: TyCon -> [PredType]
    tyConStupidTheta (AlgTyCon {algTcStupidTheta = stupid}) = stupid
    tyConStupidTheta (TupleTyCon {})			= []
    tyConStupidTheta tycon = pprPanic "tyConStupidTheta" (ppr tycon)

\end{code} \begin{code}

    -- | Extract the 'TyVar's bound by a type synonym and the corresponding (unsubstituted) right hand side.
    -- If the given 'TyCon' is not a type synonym, panics
    synTyConDefn :: TyCon -> ([TyVar], Type)
    synTyConDefn (SynTyCon {tyConTyVars = tyvars, synTcRhs = SynonymTyCon ty})
      = (tyvars, ty)
    synTyConDefn tycon = pprPanic "getSynTyConDefn" (ppr tycon)

    -- | Extract the information pertaining to the right hand side of a type synonym (@type@) declaration. Panics
    -- if the given 'TyCon' is not a type synonym
    synTyConRhs :: TyCon -> SynTyConRhs
    synTyConRhs (SynTyCon {synTcRhs = rhs}) = rhs
    synTyConRhs tc				= pprPanic "synTyConRhs" (ppr tc)

    -- | Find the expansion of the type synonym represented by the given 'TyCon'. The free variables of this
    -- type will typically include those 'TyVar's bound by the 'TyCon'. Panics if the 'TyCon' is not that of
    -- a type synonym
    synTyConType :: TyCon -> Type
    synTyConType tc = case synTcRhs tc of
    		    SynonymTyCon t -> t
    		    _		   -> pprPanic "synTyConType" (ppr tc)

\end{code} \begin{code}

    -- | If the given 'TyCon' has a /single/ data constructor, i.e. it is a @data@ type with one
    -- alternative, a tuple type or a @newtype@ then that constructor is returned. If the 'TyCon'
    -- has more than one constructor, or represents a primitive or function type constructor then
    -- @Nothing@ is returned. In any other case, the function panics
    tyConSingleDataCon_maybe :: TyCon -> Maybe DataCon
    tyConSingleDataCon_maybe (TupleTyCon {dataCon = c}) 			       = Just c
    tyConSingleDataCon_maybe (AlgTyCon {algTcRhs = DataTyCon { data_cons = [c] }}) = Just c
    tyConSingleDataCon_maybe (AlgTyCon {algTcRhs = NewTyCon { data_con = c }})     = Just c
    tyConSingleDataCon_maybe _                           			       = Nothing

\end{code} \begin{code}

    -- | Is this 'TyCon' that for a class instance?
    isClassTyCon :: TyCon -> Bool
    isClassTyCon (AlgTyCon {algTcParent = ClassTyCon _}) = True
    isClassTyCon _                                       = False

    -- | If this 'TyCon' is that for a class instance, return the class it is for.
    -- Otherwise returns @Nothing@
    tyConClass_maybe :: TyCon -> Maybe Class
    tyConClass_maybe (AlgTyCon {algTcParent = ClassTyCon clas}) = Just clas
    tyConClass_maybe _                                          = Nothing

    ----------------------------------------------------------------------------
    tyConParent :: TyCon -> TyConParent
    tyConParent (AlgTyCon {algTcParent = parent}) = parent
    tyConParent (SynTyCon {synTcParent = parent}) = parent
    tyConParent _                                 = NoParentTyCon

    -- | Is this 'TyCon' that for a family instance, be that for a synonym or an
    -- algebraic family instance?
    isFamInstTyCon :: TyCon -> Bool
    isFamInstTyCon tc = case tyConParent tc of
                          FamInstTyCon {} -> True
                          _               -> False

    tyConFamInstSig_maybe :: TyCon -> Maybe (TyCon, [Type], TyCon)
    tyConFamInstSig_maybe tc
      = case tyConParent tc of
          FamInstTyCon f ts co_tc -> Just (f, ts, co_tc)
          _                       -> Nothing

    -- | If this 'TyCon' is that of a family instance, return the family in question
    -- and the instance types. Otherwise, return @Nothing@
    tyConFamInst_maybe :: TyCon -> Maybe (TyCon, [Type])
    tyConFamInst_maybe tc
      = case tyConParent tc of
          FamInstTyCon f ts _ -> Just (f, ts)
          _                   -> Nothing

    -- | If this 'TyCon' is that of a family instance, return a 'TyCon' which represents
    -- a coercion identifying the representation type with the type instance family.
    -- Otherwise, return @Nothing@
    tyConFamilyCoercion_maybe :: TyCon -> Maybe TyCon
    tyConFamilyCoercion_maybe tc
      = case tyConParent tc of
          FamInstTyCon _ _ co -> Just co
          _                   -> Nothing

\end{code} %************************************************************************ %* * \subsection[TyCon-instances]{Instance declarations for @TyCon@} %* * %************************************************************************ @TyCon@s are compared by comparing their @Unique@s. The strictness analyser needs @Ord@. It is a lexicographic order with the property @(a<=b) || (b<=a)@. \begin{code}

    instance Eq TyCon where
        a == b = case (a `compare` b) of { EQ -> True;   _ -> False }
        a /= b = case (a `compare` b) of { EQ -> False;  _ -> True  }

    instance Ord TyCon where
        a <= b = case (a `compare` b) of { LT -> True;  EQ -> True;  GT -> False }
        a <	 b = case (a `compare` b) of { LT -> True;  EQ -> False; GT -> False }
        a >= b = case (a `compare` b) of { LT -> False; EQ -> True;  GT -> True  }
        a >	 b = case (a `compare` b) of { LT -> False; EQ -> False; GT -> True  }
        compare a b = getUnique a `compare` getUnique b

    instance Uniquable TyCon where
        getUnique tc = tyConUnique tc

    instance Outputable CoTyConDesc where
        ppr CoSym    = ptext (sLit "SYM")
        ppr CoTrans  = ptext (sLit "TRANS")
        ppr CoLeft   = ptext (sLit "LEFT")
        ppr CoRight  = ptext (sLit "RIGHT")
        ppr CoCsel1  = ptext (sLit "CSEL1")
        ppr CoCsel2  = ptext (sLit "CSEL2")
        ppr CoCselR  = ptext (sLit "CSELR")
        ppr CoInst   = ptext (sLit "INST")
        ppr CoUnsafe = ptext (sLit "UNSAFE")
        ppr (CoAxiom {}) = ptext (sLit "AXIOM")

    instance Outputable TyCon where
        ppr tc  = ppr (getName tc)

    instance NamedThing TyCon where
        getName = tyConName

    instance Data.Typeable TyCon where
        typeOf _ = Data.mkTyConApp (Data.mkTyCon "TyCon") []

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

\end{code}