ghc-6.10.3: The GHC APIContentsIndex
TyCon
Contents
Main TyCon data types
Constructing TyCons
Predicates on TyCons
Extracting information out of TyCons
Manipulating TyCons
Primitive representations of Types
Synopsis
data TyCon
type FieldLabel = Name
data AlgTyConRhs
= AbstractTyCon
| OpenTyCon {
otArgPoss :: AssocFamilyPermutation
}
| DataTyCon {
data_cons :: [DataCon]
is_enum :: Bool
}
| NewTyCon {
data_con :: DataCon
nt_rhs :: Type
nt_etad_rhs :: ([TyVar], Type)
nt_co :: Maybe TyCon
}
visibleDataCons :: AlgTyConRhs -> [DataCon]
data TyConParent
= NoParentTyCon
| ClassTyCon Class
| FamilyTyCon TyCon [Type] TyCon
data SynTyConRhs
= OpenSynTyCon Kind AssocFamilyPermutation
| SynonymTyCon Type
type AssocFamilyPermutation = Maybe [Int]
mkAlgTyCon :: Name -> Kind -> [TyVar] -> [PredType] -> AlgTyConRhs -> [Id] -> TyConParent -> RecFlag -> Bool -> Bool -> TyCon
mkClassTyCon :: Name -> Kind -> [TyVar] -> AlgTyConRhs -> Class -> RecFlag -> TyCon
mkFunTyCon :: Name -> Kind -> TyCon
mkPrimTyCon :: Name -> Kind -> Arity -> PrimRep -> TyCon
mkVoidPrimTyCon :: Name -> Kind -> Arity -> TyCon
mkLiftedPrimTyCon :: Name -> Kind -> Arity -> PrimRep -> TyCon
mkTupleTyCon :: Name -> Kind -> Arity -> [TyVar] -> DataCon -> Boxity -> Bool -> TyCon
mkSynTyCon :: Name -> Kind -> [TyVar] -> SynTyConRhs -> TyConParent -> TyCon
mkSuperKindTyCon :: Name -> TyCon
mkCoercionTyCon :: Name -> Arity -> ([Type] -> (Type, Type)) -> TyCon
mkForeignTyCon :: Name -> Maybe FastString -> Kind -> Arity -> TyCon
isAlgTyCon :: TyCon -> Bool
isClassTyCon :: TyCon -> Bool
isFamInstTyCon :: TyCon -> Bool
isFunTyCon :: TyCon -> Bool
isPrimTyCon :: TyCon -> Bool
isTupleTyCon :: TyCon -> Bool
isUnboxedTupleTyCon :: TyCon -> Bool
isBoxedTupleTyCon :: TyCon -> Bool
isSynTyCon :: TyCon -> Bool
isClosedSynTyCon :: TyCon -> Bool
isOpenSynTyCon :: TyCon -> Bool
isSuperKindTyCon :: TyCon -> Bool
isCoercionTyCon :: TyCon -> Bool
isCoercionTyCon_maybe :: TyCon -> Maybe (Arity, [Type] -> (Type, Type))
isForeignTyCon :: TyCon -> Bool
isDataTyCon :: TyCon -> Bool
isProductTyCon :: TyCon -> Bool
isEnumerationTyCon :: TyCon -> Bool
isNewTyCon :: TyCon -> Bool
isAbstractTyCon :: TyCon -> Bool
isOpenTyCon :: TyCon -> Bool
isUnLiftedTyCon :: TyCon -> Bool
isGadtSyntaxTyCon :: TyCon -> Bool
isTyConAssoc :: TyCon -> Bool
isRecursiveTyCon :: TyCon -> Bool
isHiBootTyCon :: TyCon -> Bool
isImplicitTyCon :: TyCon -> Bool
tyConHasGenerics :: TyCon -> Bool
tyConName :: TyCon -> Name
tyConKind :: TyCon -> Kind
tyConUnique :: TyCon -> Unique
tyConTyVars :: TyCon -> [TyVar]
tyConDataCons :: TyCon -> [DataCon]
tyConDataCons_maybe :: TyCon -> Maybe [DataCon]
tyConSingleDataCon_maybe :: TyCon -> Maybe DataCon
tyConFamilySize :: TyCon -> Int
tyConSelIds :: TyCon -> [Id]
tyConStupidTheta :: TyCon -> [PredType]
tyConArity :: TyCon -> Arity
tyConClass_maybe :: TyCon -> Maybe Class
tyConFamInst_maybe :: TyCon -> Maybe (TyCon, [Type])
tyConFamilyCoercion_maybe :: TyCon -> Maybe TyCon
synTyConDefn :: TyCon -> ([TyVar], Type)
synTyConRhs :: TyCon -> SynTyConRhs
synTyConType :: TyCon -> Type
synTyConResKind :: TyCon -> Kind
tyConExtName :: TyCon -> Maybe FastString
algTyConRhs :: TyCon -> AlgTyConRhs
newTyConRhs :: TyCon -> ([TyVar], Type)
newTyConEtadRhs :: TyCon -> ([TyVar], Type)
unwrapNewTyCon_maybe :: TyCon -> Maybe ([TyVar], Type, Maybe TyCon)
assocTyConArgPoss_maybe :: TyCon -> Maybe [Int]
tupleTyConBoxity :: TyCon -> Boxity
tcExpandTyCon_maybe :: TyCon -> [Type] -> Maybe ([(TyVar, Type)], Type, [Type])
coreExpandTyCon_maybe :: TyCon -> [Type] -> Maybe ([(TyVar, Type)], Type, [Type])
makeTyConAbstract :: TyCon -> TyCon
newTyConCo_maybe :: TyCon -> Maybe TyCon
setTyConArgPoss :: [TyVar] -> TyCon -> TyCon
data PrimRep
= VoidRep
| PtrRep
| IntRep
| WordRep
| Int64Rep
| Word64Rep
| AddrRep
| FloatRep
| DoubleRep
tyConPrimRep :: TyCon -> PrimRep
primRepSizeW :: PrimRep -> Int
Main TyCon data types
data TyCon

Represents 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.

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type FieldLabel = Name
Names of the fields in an algebraic record type
data AlgTyConRhs
Represents right-hand-sides of TyCons for algebraic types
Constructors
AbstractTyConSays 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.
OpenTyCon

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 :: *
otArgPoss :: AssocFamilyPermutation
DataTyConInformation about those TyCons derived from a data declaration. This includes data types with no constructors at all.
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

is_enum :: BoolCached value: is this an enumeration type? (See isEnumerationTyCon)
NewTyConInformation about those TyCons derived from a newtype declaration
data_con :: DataConThe 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 newtypes do not exist at runtime so need a different representation type).

The free TyVars 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 TyVars in this field may be shorter than the declared arity of the TyCon.
nt_co :: Maybe TyCon

A TyCon (which is always a CoercionTyCon) that can have a Coercion extracted from it to create the newtype from the representation Type.

This field is optional for non-recursive newtypes only.

visibleDataCons :: AlgTyConRhs -> [DataCon]

Extract those DataCons 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!

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 TyCons.

data TyConParent
Constructors
NoParentTyConAn ordinary type constructor has no parent.
ClassTyCon ClassType constructors representing a class dictionary.
FamilyTyCon TyCon [Type] TyCon

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 CoercionTyCon identifying the representation type with the type instance family

data SynTyConRhs
Information pertaining to the expansion of a type synonym (type)
Constructors
OpenSynTyCon Kind AssocFamilyPermutation
SynonymTyCon TypeThe synonym mentions head type variables. It acts as a template for the expansion when the TyCon is applied to some types.
type AssocFamilyPermutation = Maybe [Int]
Constructing TyCons
mkAlgTyCon
:: Name
-> KindKind of the resulting TyCon
-> [TyVar]TyVars scoped over: see tyConTyVars. Arity is inferred from the length of this list
-> [PredType]Stupid theta: see algTcStupidTheta
-> AlgTyConRhsInformation about dat aconstructors
-> [Id]Selector Ids
-> TyConParent
-> RecFlagIs the TyCon recursive?
-> BoolDoes it have generic functions? See hasGenerics
-> BoolWas the TyCon declared with GADT syntax?
-> TyCon
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)
mkClassTyCon :: Name -> Kind -> [TyVar] -> AlgTyConRhs -> Class -> RecFlag -> TyCon
Simpler specialization of mkAlgTyCon for classes
mkFunTyCon :: Name -> Kind -> TyCon
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
mkPrimTyCon :: Name -> Kind -> Arity -> PrimRep -> TyCon
Create an unlifted primitive TyCon, such as Int#
mkVoidPrimTyCon :: Name -> Kind -> Arity -> TyCon
Create the special void TyCon which is unlifted and has VoidRep
mkLiftedPrimTyCon :: Name -> Kind -> Arity -> PrimRep -> TyCon
Create a lifted primitive TyCon such as RealWorld
mkTupleTyCon
:: Name
-> KindKind of the resulting TyCon
-> ArityArity of the tuple
-> [TyVar]TyVars scoped over: see tyConTyVars
-> DataCon
-> BoxityWhether the tuple is boxed or unboxed
-> BoolDoes it have generic functions? See hasGenerics
-> TyCon
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 thunkT
mkSynTyCon :: Name -> Kind -> [TyVar] -> SynTyConRhs -> TyConParent -> TyCon
Create a type synonym TyCon
mkSuperKindTyCon :: Name -> TyCon
Create a super-kind TyCon
mkCoercionTyCon :: Name -> Arity -> ([Type] -> (Type, Type)) -> TyCon
Create a coercion TyCon
mkForeignTyCon
:: Name
-> Maybe FastStringName of the foreign imported thing, maybe
-> Kind
-> Arity
-> TyCon
Predicates on TyCons
isAlgTyCon :: TyCon -> Bool
Returns True if the supplied TyCon resulted from either a data or newtype declaration
isClassTyCon :: TyCon -> Bool
Is this TyCon that for a class instance?
isFamInstTyCon :: TyCon -> Bool
Is this TyCon that for a family instance, be that for a synonym or an algebraic family instance?
isFunTyCon :: TyCon -> Bool
isPrimTyCon :: TyCon -> Bool
Does this TyCon represent something that cannot be defined in Haskell?
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.

isUnboxedTupleTyCon :: TyCon -> Bool
Is this the TyCon for an unboxed tuple?
isBoxedTupleTyCon :: TyCon -> Bool
Is this the TyCon for a boxed tuple?
isSynTyCon :: 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 TyCons of any boxity and may even be recursive.

Is this a TyCon representing a type synonym (type)?

isClosedSynTyCon :: TyCon -> Bool
Is this a synonym TyCon that can have no further instances appear?
isOpenSynTyCon :: TyCon -> Bool
Is this a synonym TyCon that can have may have further instances appear?
isSuperKindTyCon :: TyCon -> Bool
Is this a super-kind TyCon?
isCoercionTyCon :: TyCon -> Bool
Is this a TyCon that represents a coercion?
isCoercionTyCon_maybe :: TyCon -> Maybe (Arity, [Type] -> (Type, Type))
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
isForeignTyCon :: TyCon -> Bool
Is this the TyCon of a foreign-imported type constructor?
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 newtypes, unboxed tuples and type family TyCons. But it is not guarenteed to return True in all cases that it could.

NB: for a data type family, only the instance TyCons get an info table. The family declaration TyCon does not

isProductTyCon :: TyCon -> Bool
isEnumerationTyCon :: TyCon -> Bool
Is this an algebraic TyCon which is just an enumeration of values?
isNewTyCon :: TyCon -> Bool
Is this TyCon that for a newtype
isAbstractTyCon :: TyCon -> Bool
Test if the TyCon is algebraic but abstract (invisible data constructors)
isOpenTyCon :: TyCon -> Bool
Is this a TyCon, synonym or otherwise, that may have further instances appear?
isUnLiftedTyCon :: TyCon -> Bool
Is this TyCon unlifted (i.e. cannot contain bottom)? Note that this can only be true for primitive and unboxed-tuple TyCons
isGadtSyntaxTyCon :: TyCon -> Bool
Is this an algebraic TyCon declared with the GADT syntax?
isTyConAssoc :: TyCon -> Bool
Are we able to extract informationa TyVar to class argument list mappping from a given TyCon?
isRecursiveTyCon :: TyCon -> Bool
Is this a recursive TyCon?
isHiBootTyCon :: TyCon -> Bool
Did this TyCon originate from type-checking a .h*-boot file?
isImplicitTyCon :: TyCon -> Bool

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).
tyConHasGenerics :: TyCon -> Bool
Does this TyCon have any generic to/from functions available? See also hasGenerics
Extracting information out of TyCons
tyConName :: TyCon -> Name
tyConKind :: TyCon -> Kind
tyConUnique :: TyCon -> Unique
tyConTyVars :: TyCon -> [TyVar]
tyConDataCons :: TyCon -> [DataCon]
As tyConDataCons_maybe, but returns the empty list of constructors if no constructors could be found
tyConDataCons_maybe :: TyCon -> Maybe [DataCon]
Determine the DataCons originating from the given TyCon, if the TyCon is the sort that can have any constructors (note: this does not include abstract algebraic types)
tyConSingleDataCon_maybe :: TyCon -> Maybe DataCon
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
tyConFamilySize :: TyCon -> Int
Determine the number of value constructors a TyCon has. Panics if the TyCon is not algebraic or a tuple
tyConSelIds :: TyCon -> [Id]
Extract the record selector Ids from an algebraic TyCon and returns the empty list otherwise
tyConStupidTheta :: TyCon -> [PredType]
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 ...
tyConArity :: TyCon -> Arity
tyConClass_maybe :: TyCon -> Maybe Class
If this TyCon is that for a class instance, return the class it is for. Otherwise returns Nothing
tyConFamInst_maybe :: TyCon -> Maybe (TyCon, [Type])
If this TyCon is that of a family instance, return the family in question and the instance types. Otherwise, return Nothing
tyConFamilyCoercion_maybe :: TyCon -> Maybe TyCon
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
synTyConDefn :: TyCon -> ([TyVar], Type)
Extract the TyVars bound by a type synonym and the corresponding (unsubstituted) right hand side. If the given TyCon is not a type synonym, panics
synTyConRhs :: TyCon -> SynTyConRhs
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
synTyConType :: TyCon -> Type
Find the expansion of the type synonym represented by the given TyCon. The free variables of this type will typically include those TyVars bound by the TyCon. Panics if the TyCon is not that of a type synonym
synTyConResKind :: TyCon -> Kind
Find the Kind of an open type synonym. Panics if the TyCon is not an open type synonym
tyConExtName :: TyCon -> Maybe FastString
Just e for foreign-imported types, holds the name of the imported thing
algTyConRhs :: TyCon -> AlgTyConRhs
Extract an AlgTyConRhs with information about data constructors from an algebraic or tuple TyCon. Panics for any other sort of TyCon
newTyConRhs :: TyCon -> ([TyVar], Type)
Extract the bound type variables and type expansion of a type synonym TyCon. Panics if the TyCon is not a synonym
newTyConEtadRhs :: TyCon -> ([TyVar], Type)
Extract the bound type variables and type expansion of an eta-contracted type synonym TyCon. Panics if the TyCon is not a synonym
unwrapNewTyCon_maybe :: TyCon -> Maybe ([TyVar], Type, Maybe TyCon)
Take a TyCon apart into the TyVars 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.
assocTyConArgPoss_maybe :: TyCon -> Maybe [Int]
Extract the mapping from TyVar indexes to indexes in the corresponding family argument lists form an open TyCon of any sort, if the given TyCon is indeed such a beast and that information is available
tupleTyConBoxity :: TyCon -> Boxity
Extract the boxity of the given TyCon, if it is a TupleTyCon. Panics otherwise
Manipulating TyCons
tcExpandTyCon_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 TyCons. We expand (closed) synonyms only, cf. coreExpandTyCon_maybe

Used to create the view Core has on TyCons. We expand not only closed synonyms like tcExpandTyCon_maybe, but also non-recursive newtypes

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
makeTyConAbstract :: TyCon -> TyCon
Make an algebraic TyCon abstract. Panics if the supplied TyCon is not algebraic
newTyConCo_maybe :: TyCon -> Maybe TyCon
Extracts the newtype coercion from such a TyCon, which can be used to construct something with the newtypes type from its representation type (right hand side). If the supplied TyCon is not a newtype, returns Nothing
setTyConArgPoss :: [TyVar] -> TyCon -> TyCon
Set the AssocFamilyPermutation structure in an associated data or type synonym. The [TyVar] are the class type variables. Remember, the tyvars of an associated data/type are a subset of the class tyvars; except that an associated data type can have extra type variables at the end (see Note [Avoid name clashes for associated data types] in TcHsType)
Primitive representations of Types
data PrimRep
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.
Constructors
VoidRep
PtrRep
IntRepSigned, word-sized value
WordRepUnsigned, word-sized value
Int64RepSigned, 64 bit value (with 32-bit words only)
Word64RepUnsigned, 64 bit value (with 32-bit words only)
AddrRepA pointer, but not to a Haskell value (use PtrRep)
FloatRep
DoubleRep
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tyConPrimRep :: TyCon -> PrimRep
Find the primitive representation of a TyCon
primRepSizeW :: PrimRep -> Int
Find the size of a PrimRep, in words
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