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 *

This data type also encodes a number of primitive, built in type constructors such as those for function and tuple types.

Represents right-hand-sides of TyCons for algebraic types

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.

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!

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

Some promoted datacons signify extra info relevant to GHC. For example, the IntRep constructor of RuntimeRep corresponds to the IntRep constructor of PrimRep. This data structure allows us to store this information right in the TyCon. The other approach would be to look up things like RuntimeRep's PrimRep by known-key every time.

The labels for the fields of this particular TyCon

The labels for the fields of this particular 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)

Simpler specialization of mkAlgTyCon for classes

Given the name of the function type constructor and it's kind, create the corresponding TyCon. It is reccomended to use funTyCon if you want this functionality

Create an unlifted primitive TyCon, such as Int#

Kind constructors

Create a lifted primitive TyCon such as RealWorld

Create a type synonym TyCon

Create a type family TyCon

Create a promoted data constructor TyCon Somewhat dodgily, we give it the same Name as the data constructor itself; when we pretty-print the TyCon we add a quote; see the Outputable TyCon instance

Makes a tycon suitable for use during type-checking. The only real need for this is for printing error messages during a recursive type/class type-checking knot. It has a kind because TcErrors sometimes calls typeKind. See also Note [Kind checking recursive type and class declarations] in TcTyClsDecls.

Returns True if the supplied TyCon resulted from either a data or newtype declaration

Returns True for vanilla AlgTyCons -- that is, those created with a data or newtype declaration.

Is this TyCon that for a class instance?

Is this TyCon that for a data family instance?

Does this TyCon represent something that cannot be defined in Haskell?

Does this TyCon represent a tuple?

NB: when compiling Data.Tuple, the tycons won't reply True to isTupleTyCon, because they are built as AlgTyCons. However they get spat into the interface file as tuple tycons, so I don't think it matters.

Is this the TyCon for an unboxed tuple?

Is this the TyCon for a boxed tuple?

Is this a TyCon representing a regular H98 type synonym (type)?

True iff we can decompose (T a b c) into ((T a b) c) I.e. is it injective and generative w.r.t nominal equality? That is, if (T a b) ~N d e f, is it always the case that (T ~N d), (a ~N e) and (b ~N f)? Specifically NOT true of synonyms (open and otherwise)

It'd be unusual to call mightBeUnsaturatedTyCon on a regular H98 type synonym, because you should probably have expanded it first But regardless, it's not decomposable

Is this a PromotedDataCon?

Retrieves the promoted DataCon if this is a PromotedDataCon;

Is this tycon really meant for use at the kind level? That is, should it be permitted without -XDataKinds?

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 guaranteed 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

Is this an algebraic TyCon which is just an enumeration of values?

Is this TyCon that for a newtype

Test if the TyCon is algebraic but abstract (invisible data constructors)

Is this a TyCon, synonym or otherwise, that defines a family?

Is this a TyCon, synonym or otherwise, that defines a family with instances?

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

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

Is this an open type family TyCon?

Is this a non-empty closed type family? Returns Nothing for abstract or empty closed families.

Try to read the injectivity information from a FamilyTyCon. For every other TyCon this function panics.

Is this TyCon unlifted (i.e. cannot contain bottom)? Note that this can only be true for primitive and unboxed-tuple TyCons

Is this an algebraic TyCon declared with the GADT syntax?

isInjectiveTyCon is true of TyCons for which this property holds (where X is the role passed in): If (T a1 b1 c1) ~X (T a2 b2 c2), then (a1 ~X1 a2), (b1 ~X2 b2), and (c1 ~X3 c2) (where X1, X2, and X3, are the roles given by tyConRolesX tc X) See also Note [Decomposing equalities] in TcCanonical

isGenerativeTyCon is true of TyCons for which this property holds (where X is the role passed in): If (T tys ~X t), then (t's head ~X T). See also Note [Decomposing equalities] in TcCanonical

Is this an AlgTyConRhs of a TyCon that is generative and injective with respect to representational equality?

Are we able to extract information TyVar to class argument list mapping from a given TyCon?

Is this a recursive TyCon?

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).
• Tuples are implicit iff they have a wired-in name (namely: boxed and unboxed tupeles are wired-in and implicit, but constraint tuples are not)

Check if the tycon actually refers to a proper `data` or `newtype` with user defined constructors rather than one from a class or other construction.

Is this a TcTyCon? (That is, one only used during type-checking?)

Name of the constructor

Kind of this TyCon (full kind, not just the return kind)

A Unique of this TyCon. Invariant: identical to Unique of Name stored in tyConName field.

The kind and 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.

The C type that should be used for this type when using the FFI and CAPI

As tyConDataCons_maybe, but returns the empty list of constructors if no constructors could be found

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)

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

Determine the number of value constructors a TyCon has. Panics if the TyCon is not algebraic or a tuple

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 ...

Number of arguments this TyCon must receive to be considered saturated (including implicit kind variables)

Get the list of roles for the type parameters of a TyCon

If this TyCon is that for a class instance, return the class it is for. Otherwise returns Nothing

Return the associated types of the TyCon, if any

If this TyCon is that of a data family instance, return the family in question and the instance types. Otherwise, return Nothing

If this TyCon is that of a data family instance, return a TyCon which represents a coercion identifying the representation type with the type instance family. Otherwise, return Nothing

Extract type variable naming the result of injective type family

Extract the TyVars bound by a vanilla type synonym and the corresponding (unsubstituted) right hand side.

Extract the information pertaining to the right hand side of a type synonym (type) declaration.

Extract the flavour of a type family (with all the extra information that it carries)

Name of result type variable, used for pretty-printing with --show-iface and for reifying TyCon in Template Haskell

Extract an AlgTyConRhs with information about data constructors from an algebraic or tuple TyCon. Panics for any other sort of TyCon

Extract the bound type variables and type expansion of a type synonym TyCon. Panics if the TyCon is not a synonym

The number of type parameters that need to be passed to a newtype to resolve it. May be less than in the definition if it can be eta-contracted.

Extract the bound type variables and type expansion of an eta-contracted type synonym TyCon. Panics if the TyCon is not a synonym

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.

Maps a label to information about the field

Extract any RuntimeRepInfo from this TyCon

The TyBinders for this TyCon's kind. length tyConBinders == tyConArity. This is a cached value and is redundant with the tyConKind.

Cached result kind

Scoped tyvars over the tycon's body. See Note [TcTyCon]

Expand a type synonym application, if any

Make an fake, abstract TyCon from an existing one. Used when recovering from errors

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

Make a Name for the Typeable representation of the given wired-in type

The name (and defining module) for the Typeable representation (TyCon) of a type constructor.

See Note [Grand plan for Typeable] in TcTypeable in TcTypeable.

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.

Find the size of a PrimRep, in words

Return if Rep stands for floating type, returns Nothing for vector types.