Notes about type families
-----------------------------------------------
-Type synonym families
-~~~~~~~~~~~~~~~~~~~~~~
+Note [Type synonym families]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Type synonym families, also known as "type functions", map directly
onto the type functions in FC:
--
-- 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
+-- 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.
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.
+ -- | 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'
+ 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.
+ -- | Represents the infinite family of tuple type constructors,
+ -- @()@, @(a,b)@, @(# a, b #)@ etc.
| TupleTyCon {
tyConUnique :: Unique,
tyConName :: Name,
tyConTyVars :: [TyVar], -- Bound tyvars
- synTcRhs :: SynTyConRhs, -- ^ Contains information about the expansion of the synonym
+ synTcRhs :: SynTyConRhs, -- ^ Contains information about the
+ -- expansion of the synonym
- synTcParent :: TyConParent -- ^ Gives the family declaration 'TyCon' of 'TyCon's representing family instances
+ 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
+ -- | 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!
+ 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 = *
+ 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
+ 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
+ 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@.
-- 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. 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 {
-- | 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.
+ -- | 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 assoicated data type declaration, within a class declaration:
- --
- -- > class C a b where
- -- > data T b :: *
-
+ -- | 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 assoicated data type declaration, within a class declaration:
+ --
+ -- > class C a b where
+ -- > data T b :: *
| OpenTyCon {
otArgPoss :: AssocFamilyPermutation
}
- -- | Information about those 'TyCon's derived from a @data@ declaration. This includes
- -- data types with no constructors at all.
+ -- | 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 'isEnumerationTyCon')
+ -- ^ 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 'isEnumerationTyCon')
}
-- | Information about those 'TyCon's derived from a @newtype@ declaration
| NewTyCon {
- data_con :: DataCon, -- ^ The unique constructor for the @newtype@. It has no existentials
+ 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).
+ 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'
+ -- 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'.
+ -- ^ 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.
+ 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.
}
type AssocFamilyPermutation
-- TyCon's arity; e.g. class C a where { data D a :: *->* }
-- here D gets arity 2
--- | 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!
+-- | 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 OpenTyCon {} = []
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)
+-- | 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
+ -> [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
isUnLiftedTyCon (TupleTyCon {tyConBoxed = boxity}) = not (isBoxed boxity)
isUnLiftedTyCon _ = False
--- | Returns @True@ if the supplied 'TyCon' resulted from either a @data@ or @newtype@ declaration
+-- | Returns @True@ if the supplied 'TyCon' resulted from either a
+-- @data@ or @newtype@ declaration
isAlgTyCon :: TyCon -> Bool
isAlgTyCon (AlgTyCon {}) = True
isAlgTyCon (TupleTyCon {}) = True
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