ghc-7.0.3: The GHC API

DataCon

Contents

- Main data types
  - Type construction
  - Type deconstruction
  - Predicates on DataCons
- Splitting product types

Synopsis

- data DataCon
- data DataConIds = DCIds (Maybe Id) Id
- type ConTag = Int
- mkDataCon :: Name -> Bool -> [HsBang] -> [FieldLabel] -> [TyVar] -> [TyVar] -> [(TyVar, Type)] -> ThetaType -> [Type] -> Type -> TyCon -> ThetaType -> DataConIds -> DataCon
- fIRST_TAG :: ConTag
- dataConRepType :: DataCon -> Type
- dataConSig :: DataCon -> ([TyVar], ThetaType, [Type], Type)
- dataConFullSig :: DataCon -> ([TyVar], [TyVar], [(TyVar, Type)], ThetaType, ThetaType, [Type], Type)
- dataConName :: DataCon -> Name
- dataConIdentity :: DataCon -> [Word8]
- dataConTag :: DataCon -> ConTag
- dataConTyCon :: DataCon -> TyCon
- dataConOrigTyCon :: DataCon -> TyCon
- dataConUserType :: DataCon -> Type
- dataConUnivTyVars :: DataCon -> [TyVar]
- dataConExTyVars :: DataCon -> [TyVar]
- dataConAllTyVars :: DataCon -> [TyVar]
- dataConEqSpec :: DataCon -> [(TyVar, Type)]
- eqSpecPreds :: [(TyVar, Type)] -> ThetaType
- dataConEqTheta :: DataCon -> ThetaType
- dataConDictTheta :: DataCon -> ThetaType
- dataConStupidTheta :: DataCon -> ThetaType
- dataConInstArgTys :: DataCon -> [Type] -> [Type]
- dataConOrigArgTys :: DataCon -> [Type]
- dataConOrigResTy :: DataCon -> Type
- dataConInstOrigArgTys :: DataCon -> [Type] -> [Type]
- dataConRepArgTys :: DataCon -> [Type]
- dataConFieldLabels :: DataCon -> [FieldLabel]
- dataConFieldType :: DataCon -> FieldLabel -> Type
- dataConStrictMarks :: DataCon -> [HsBang]
- dataConExStricts :: DataCon -> [HsBang]
- dataConSourceArity :: DataCon -> Arity
- dataConRepArity :: DataCon -> Int
- dataConIsInfix :: DataCon -> Bool
- dataConWorkId :: DataCon -> Id
- dataConWrapId :: DataCon -> Id
- dataConWrapId_maybe :: DataCon -> Maybe Id
- dataConImplicitIds :: DataCon -> [Id]
- dataConRepStrictness :: DataCon -> [StrictnessMark]
- isNullarySrcDataCon :: DataCon -> Bool
- isNullaryRepDataCon :: DataCon -> Bool
- isTupleCon :: DataCon -> Bool
- isUnboxedTupleCon :: DataCon -> Bool
- isVanillaDataCon :: DataCon -> Bool
- classDataCon :: Class -> DataCon
- splitProductType_maybe :: Type -> Maybe (TyCon, [Type], DataCon, [Type])
- splitProductType :: String -> Type -> (TyCon, [Type], DataCon, [Type])
- deepSplitProductType :: String -> Type -> (TyCon, [Type], DataCon, [Type])
- deepSplitProductType_maybe :: Type -> Maybe (TyCon, [Type], DataCon, [Type])

# Main data types

data DataCon

A data constructor

Instances

Eq DataCon |
Data DataCon |
Ord DataCon |
Show DataCon |
Typeable DataCon |
Outputable DataCon |
Uniquable DataCon |
NamedThing DataCon |

data DataConIds

Contains the Ids of the data constructor functions

Constructors

DCIds (Maybe Id) Id |

type ConTag = Int

Type of the tags associated with each constructor possibility

## Type construction

mkDataCon

Arguments

:: Name |
-> Bool | Is the constructor declared infix?
-> [HsBang] | Strictness annotations written in the source file
-> [FieldLabel] | Field labels for the constructor, if it is a record, otherwise empty
-> [TyVar] | Universally quantified type variables
-> [TyVar] | Existentially quantified type variables
-> [(TyVar, Type)] | GADT equalities
-> ThetaType | Theta-type occuring before the arguments proper
-> [Type] | Original argument types
-> Type | Original result type
-> TyCon | Representation type constructor
-> ThetaType | The stupid theta, context of the data declaration e.g. `data Eq a => T a ...`
-> DataConIds | The Ids of the actual builder functions
-> DataCon |

Build a new data constructor

fIRST_TAG :: ConTag

Tags are allocated from here for real constructors

## Type deconstruction

dataConRepType :: DataCon -> Type

The representation type of the data constructor, i.e. the sort type that will represent values of this type at runtime

dataConSig :: DataCon -> ([TyVar], ThetaType, [Type], Type)

The "signature" of the `DataCon` returns, in order:

1) The result of `dataConAllTyVars`,

2) All the `ThetaType`s relating to the `DataCon` (coercion, dictionary, implicit parameter - whatever)

3) The type arguments to the constructor

4) The original result type of the `DataCon`

dataConFullSig :: DataCon -> ([TyVar], [TyVar], [(TyVar, Type)], ThetaType, ThetaType, [Type], Type)

The "full signature" of the `DataCon` returns, in order:

1) The result of `dataConUnivTyVars`

2) The result of `dataConExTyVars`

3) The result of `dataConEqSpec`

4) The result of `dataConDictTheta`

5) The original argument types to the `DataCon` (i.e. before any change of the representation of the type)

6) The original result type of the `DataCon`

dataConName :: DataCon -> Name

The `Name` of the `DataCon`, giving it a unique, rooted identification

dataConIdentity :: DataCon -> [Word8]

The string `package:module.name` identifying a constructor, which is attached to its info table and used by the GHCi debugger and the heap profiler

dataConTag :: DataCon -> ConTag

The tag used for ordering `DataCon`s

dataConTyCon :: DataCon -> TyCon

The type constructor that we are building via this data constructor

dataConOrigTyCon :: DataCon -> TyCon

The original type constructor used in the definition of this data constructor. In case of a data family instance, that will be the family type constructor.

dataConUserType :: DataCon -> Type

The user-declared type of the data constructor in the nice-to-read form:

     T :: forall a b. a -> b -> T [a]

rather than:

     T :: forall a c. forall b. (c~[a]) => a -> b -> T c

NB: If the constructor is part of a data instance, the result type mentions the family tycon, not the internal one.

dataConUnivTyVars :: DataCon -> [TyVar]

The universally-quantified type variables of the constructor

dataConExTyVars :: DataCon -> [TyVar]

The existentially-quantified type variables of the constructor

dataConAllTyVars :: DataCon -> [TyVar]

Both the universal and existentiatial type variables of the constructor

dataConEqSpec :: DataCon -> [(TyVar, Type)]

Equalities derived from the result type of the data constructor, as written by the programmer in any GADT declaration

eqSpecPreds :: [(TyVar, Type)] -> ThetaType

dataConEqTheta :: DataCon -> ThetaType

The equational constraints on the data constructor type

dataConDictTheta :: DataCon -> ThetaType

The type class and implicit parameter contsraints on the data constructor type

dataConStupidTheta :: DataCon -> ThetaType

The "stupid theta" of the `DataCon`, such as `data Eq a` in:

     data Eq a => T a = ...

dataConInstArgTys

Arguments

:: DataCon | A datacon with no existentials or equality constraints However, it can have a dcTheta (notably it can be a class dictionary, with superclasses)
-> [Type] | Instantiated at these types
-> [Type] |

Finds the instantiated types of the arguments required to construct a `DataCon` representation NB: these INCLUDE any dictionary args but EXCLUDE the data-declaration context, which is discarded It's all post-flattening etc; this is a representation type

dataConOrigArgTys :: DataCon -> [Type]

Returns the argument types of the wrapper, excluding all dictionary arguments and without substituting for any type variables

dataConOrigResTy :: DataCon -> Type

dataConInstOrigArgTys :: DataCon -> [Type] -> [Type]

Returns just the instantiated value argument types of a `DataCon`, (excluding dictionary args)

dataConRepArgTys :: DataCon -> [Type]

Returns the arg types of the worker, including all dictionaries, after any flattening has been done and without substituting for any type variables

dataConFieldLabels :: DataCon -> [FieldLabel]

The labels for the fields of this particular `DataCon`

dataConFieldType :: DataCon -> FieldLabel -> Type

Extract the type for any given labelled field of the `DataCon`

dataConStrictMarks :: DataCon -> [HsBang]

The strictness markings decided on by the compiler. Does not include those for existential dictionaries. The list is in one-to-one correspondence with the arity of the `DataCon`

dataConExStricts :: DataCon -> [HsBang]

Strictness of existential arguments only

dataConSourceArity :: DataCon -> Arity

Source-level arity of the data constructor

dataConRepArity :: DataCon -> Int

Gives the number of actual fields in the representation of the data constructor. This may be more than appear in the source code; the extra ones are the existentially quantified dictionaries

dataConIsInfix :: DataCon -> Bool

Should the `DataCon` be presented infix?

dataConWorkId :: DataCon -> Id

Get the Id of the `DataCon` worker: a function that is the actual constructor and has no top level binding in the program. The type may be different from the obvious one written in the source program. Panics if there is no such `Id` for this `DataCon`

dataConWrapId :: DataCon -> Id

Returns an Id which looks like the Haskell-source constructor by using the wrapper if it exists (see `dataConWrapId_maybe`) and failing over to the worker (see `dataConWorkId`)

dataConWrapId_maybe :: DataCon -> Maybe Id

Get the Id of the `DataCon` wrapper: a function that wraps the actual constructor so it has the type visible in the source program: c.f. `dataConWorkId`. Returns Nothing if there is no wrapper, which occurs for an algebraic data constructor and also for a newtype (whose constructor is inlined compulsorily)

dataConImplicitIds :: DataCon -> [Id]

Find all the `Id`s implicitly brought into scope by the data constructor. Currently, the union of the `dataConWorkId` and the `dataConWrapId`

dataConRepStrictness :: DataCon -> [StrictnessMark]

Give the demands on the arguments of a Core constructor application (Con dc args)

## Predicates on DataCons

isNullarySrcDataCon :: DataCon -> Bool

Return whether there are any argument types for this `DataCon`s original source type

isNullaryRepDataCon :: DataCon -> Bool

Return whether there are any argument types for this `DataCon`s runtime representation type

isTupleCon :: DataCon -> Bool

isUnboxedTupleCon :: DataCon -> Bool

isVanillaDataCon :: DataCon -> Bool

Vanilla `DataCon`s are those that are nice boring Haskell 98 constructors

classDataCon :: Class -> DataCon

# Splitting product types

splitProductType_maybe

Arguments

:: Type | A product type, perhaps
-> Maybe (TyCon, [Type], DataCon, [Type]) |

Extract the type constructor, type argument, data constructor and it's representation argument types from a type if it is a product type.

Precisely, we return `Just` for any type that is all of:

- Concrete (i.e. constructors visible)
- Single-constructor
- Not existentially quantified

Whether the type is a `data` type or a `newtype`

splitProductType :: String -> Type -> (TyCon, [Type], DataCon, [Type])

As `splitProductType_maybe`, but panics if the `Type` is not a product type

deepSplitProductType :: String -> Type -> (TyCon, [Type], DataCon, [Type])

As `deepSplitProductType_maybe`, but panics if the `Type` is not a product type

deepSplitProductType_maybe :: Type -> Maybe (TyCon, [Type], DataCon, [Type])

As `splitProductType_maybe`, but in turn instantiates the `TyCon` returned and hence recursively tries to unpack it as far as it able to