ghc-7.0.3: The GHC API

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
  - | DataFamilyTyCon
  - | 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
  - | AssocFamilyTyCon Class
  - | FamInstTyCon TyCon [Type] TyCon
- isNoParent :: TyConParent -> Bool
- data SynTyConRhs
  - = SynonymTyCon Type
  - | SynFamilyTyCon
- data CoTyConDesc
  - = CoSym
  - | CoTrans
  - | CoLeft
  - | CoRight
  - | CoCsel1
  - | CoCsel2
  - | CoCselR
  - | CoInst
  - | CoAxiom {
    - co_ax_tvs :: [TyVar]
    - co_ax_lhs :: Type
    - co_ax_rhs :: Type
    }
  - | CoUnsafe
- mkAlgTyCon :: Name -> Kind -> [TyVar] -> [PredType] -> AlgTyConRhs -> TyConParent -> RecFlag -> Bool -> Bool -> TyCon
- mkClassTyCon :: Name -> Kind -> [TyVar] -> AlgTyConRhs -> Class -> RecFlag -> TyCon
- mkFunTyCon :: Name -> Kind -> TyCon
- mkPrimTyCon :: Name -> Kind -> Arity -> PrimRep -> TyCon
- mkKindTyCon :: Name -> Kind -> 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 -> CoTyConDesc -> TyCon
- mkForeignTyCon :: Name -> Maybe FastString -> Kind -> Arity -> TyCon
- mkAnyTyCon :: Name -> Kind -> 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
- isSuperKindTyCon :: TyCon -> Bool
- isDecomposableTyCon :: TyCon -> Bool
- isCoercionTyCon :: TyCon -> Bool
- isCoercionTyCon_maybe :: TyCon -> Maybe (Arity, CoTyConDesc)
- isForeignTyCon :: TyCon -> Bool
- isAnyTyCon :: TyCon -> Bool
- tyConHasKind :: TyCon -> Bool
- isInjectiveTyCon :: TyCon -> Bool
- isDataTyCon :: TyCon -> Bool
- isProductTyCon :: TyCon -> Bool
- isEnumerationTyCon :: TyCon -> Bool
- isNewTyCon :: TyCon -> Bool
- isAbstractTyCon :: TyCon -> Bool
- isFamilyTyCon :: TyCon -> Bool
- isSynFamilyTyCon :: TyCon -> Bool
- isDataFamilyTyCon :: 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
- tyConStupidTheta :: TyCon -> [PredType]
- tyConArity :: TyCon -> Arity
- tyConParent :: TyCon -> TyConParent
- tyConClass_maybe :: TyCon -> Maybe Class
- tyConFamInst_maybe :: TyCon -> Maybe (TyCon, [Type])
- tyConFamilyCoercion_maybe :: TyCon -> Maybe TyCon
- tyConFamInstSig_maybe :: TyCon -> Maybe (TyCon, [Type], TyCon)
- synTyConDefn :: TyCon -> ([TyVar], Type)
- synTyConRhs :: TyCon -> SynTyConRhs
- synTyConType :: TyCon -> Type
- tyConExtName :: TyCon -> Maybe FastString
- algTyConRhs :: TyCon -> AlgTyConRhs
- newTyConRhs :: TyCon -> ([TyVar], Type)
- newTyConEtadRhs :: TyCon -> ([TyVar], Type)
- unwrapNewTyCon_maybe :: TyCon -> Maybe ([TyVar], Type, Maybe TyCon)
- 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
- data PrimRep
  - = VoidRep
  - | PtrRep
  - | IntRep
  - | WordRep
  - | Int64Rep
  - | Word64Rep
  - | AddrRep
  - | FloatRep
  - | DoubleRep
- tyConPrimRep :: TyCon -> PrimRep
- primRepSizeW :: PrimRep -> Int

# Main TyCon data types

data TyCon

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.

Instances

Eq TyCon |
Data TyCon |
Ord TyCon |
Typeable TyCon |
Outputable TyCon |
Uniquable TyCon |
NamedThing TyCon |

type FieldLabel = Name

Names of the fields in an algebraic record type

data AlgTyConRhs

Represents right-hand-sides of `TyCon`s for algebraic types

Constructors

AbstractTyCon | 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.

DataFamilyTyCon

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 :: *

DataTyCon | Information about those `TyCon`s derived from a `data` declaration. This includes data types with no constructors at all.

Fields

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]

NewTyCon | Information about those `TyCon`s derived from a `newtype` declaration

Fields

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`.

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.

visibleDataCons :: AlgTyConRhs -> [DataCon]

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!

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

Constructors

NoParentTyCon | An ordinary type constructor has no parent.
ClassTyCon Class | Type constructors representing a class dictionary.
AssocFamilyTyCon Class | An *associated* type of a class.
FamInstTyCon 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 `CoTyCon` identifying the representation type with the type instance family

isNoParent :: TyConParent -> Bool

data SynTyConRhs

Information pertaining to the expansion of a type synonym (`type`)

Constructors

SynonymTyCon Type | An ordinary type synonyn.
SynFamilyTyCon | A type synonym family e.g. `type family F x y :: * -> *`

data CoTyConDesc

Constructors

CoSym |
CoTrans |
CoLeft |
CoRight |
CoCsel1 |
CoCsel2 |
CoCselR |
CoInst |
CoAxiom |

Fields

co_ax_tvs :: [TyVar]
co_ax_lhs :: Type
co_ax_rhs :: Type

CoUnsafe |

Instances

Outputable CoTyConDesc |

## Constructing TyCons

mkAlgTyCon

Arguments

:: 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 |

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#`

mkKindTyCon :: Name -> Kind -> TyCon

Kind constructors

mkLiftedPrimTyCon :: Name -> Kind -> Arity -> PrimRep -> TyCon

Create a lifted primitive `TyCon` such as `RealWorld`

mkTupleTyCon

Arguments

:: 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 |

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 -> CoTyConDesc -> TyCon

Create a coercion `TyCon`

mkForeignTyCon

Arguments

:: Name |
-> Maybe FastString | Name of the foreign imported thing, maybe
-> Kind |
-> Arity |
-> TyCon |

mkAnyTyCon :: Name -> Kind -> 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` `TyCon`s 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?

isSuperKindTyCon :: TyCon -> Bool

Is this a super-kind `TyCon`?

isDecomposableTyCon :: TyCon -> Bool

isCoercionTyCon :: TyCon -> Bool

Is this a `TyCon` that represents a coercion?

isCoercionTyCon_maybe :: TyCon -> Maybe (Arity, CoTyConDesc)

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?

isAnyTyCon :: TyCon -> Bool

Is this an AnyTyCon?

tyConHasKind :: TyCon -> Bool

isInjectiveTyCon :: TyCon -> Bool

Injective `TyCon`s can be decomposed, so that T ty1 ~ T ty2 => ty1 ~ ty2

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

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)

isFamilyTyCon :: TyCon -> Bool

Is this a `TyCon`, synonym or otherwise, that may have further instances appear?

isSynFamilyTyCon :: TyCon -> Bool

Is this a synonym `TyCon` that can have may have further instances appear?

isDataFamilyTyCon :: TyCon -> Bool

Is this a synonym `TyCon` that can have 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 `TyCon`s

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 `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)

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

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

tyConParent :: TyCon -> TyConParent

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`

tyConFamInstSig_maybe :: TyCon -> Maybe (TyCon, [Type], TyCon)

synTyConDefn :: TyCon -> ([TyVar], Type)

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

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 `TyVar`s bound by the `TyCon`. Panics if the `TyCon` is not that of a 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 `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.

tupleTyConBoxity :: TyCon -> Boxity

Extract the boxity of the given `TyCon`, if it is a `TupleTyCon`. Panics otherwise

## Manipulating TyCons

tcExpandTyCon_maybe

Arguments

:: 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`

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

Arguments

:: 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 `newtype`s type from its representation type (right hand side). If the supplied `TyCon` is not a `newtype`, returns `Nothing`

# 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 |
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 |

Instances

Eq PrimRep |
Show PrimRep |
Outputable PrimRep |

tyConPrimRep :: TyCon -> PrimRep

Find the primitive representation of a `TyCon`

primRepSizeW :: PrimRep -> Int

Find the size of a `PrimRep`, in words