Main data types

A data constructor

• AnnKeywordId : AnnOpen, AnnClose,AnnComma

Data Constructor Representation See Note [Data constructor workers and wrappers]

Source Strictness

What strictness annotation the user wrote

Source Unpackedness

What unpackedness the user requested

Haskell Source Bang

Bangs on data constructor arguments as the user wrote them in the source code.

(HsSrcBang _ SrcUnpack SrcLazy) and (HsSrcBang _ SrcUnpack NoSrcStrict) (without StrictData) makes no sense, we emit a warning (in checkValidDataCon) and treat it like (HsSrcBang _ NoSrcUnpack SrcLazy)

Haskell Implementation Bang

Bangs of data constructor arguments as generated by the compiler after consulting HsSrcBang, flags, etc.

A *one-index* constructor tag

Type of the tags associated with each constructor possibility or superclass selector

An EqSpec is a tyvar/type pair representing an equality made in rejigging a GADT constructor

Make a non-dependent EqSpec

Substitute in an EqSpec. Precondition: if the LHS of the EqSpec is mapped in the substitution, it is mapped to a type variable, not a full type.

Filter out any TyVars mentioned in an EqSpec.

Fields in an algebraic record type; see Note [FieldLabel].

Field labels are just represented as strings; they are not necessarily unique (even within a module)

Build a new data constructor

Tags are allocated from here for real constructors or for superclass selectors

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

Instantiate the universal tyvars of a data con, returning ( instantiated existentials , instantiated constraints including dependent GADT equalities which are *also* listed in the instantiated existentials , instantiated args)

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

1) The result of dataConUnivTyVars

2) The result of dataConExTyCoVars

3) The non-dependent GADT equalities. Dependent GADT equalities are implied by coercion variables in return value (2).

4) The other constraints of the data constructor type, excluding GADT equalities

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

6) The original result type of the DataCon

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

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

The tag used for ordering DataCons

The type constructor that we are building via this data constructor

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.

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

The type variables are quantified in the order that the user wrote them. See Note [DataCon user type variable binders].

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

The universally-quantified type variables of the constructor

The existentially-quantified type/coercion variables of the constructor including dependent (kind-) GADT equalities

Both the universal and existential type/coercion variables of the constructor

The type variables of the constructor, in the order the user wrote them

InvisTVBinders for the type variables of the constructor, in the order the user wrote them

Equalities derived from the result type of the data constructor, as written by the programmer in any GADT declaration. This includes *all* GADT-like equalities, including those written in by hand by the programmer.

The *full* constraints on the constructor type, including dependent GADT equalities.

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

data Eq a => T a = ...

See Note [The stupid context].

Returns constraints in the wrapper type, other than those in the dataConEqSpec

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

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

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

Returns the arg types of the worker, including *all* non-dependent evidence, after any flattening has been done and without substituting for any type variables

Given a data constructor dc with n universally quantified type variables a_{1}, a_{2}, ..., a_{n}, and given a list of argument types dc_args of length m where m <= n, then:

dataConInstUnivs dc dc_args

Will return:

[dc_arg_{1}, dc_arg_{2}, ..., dc_arg_{m}, a_{m+1}, ..., a_{n}]

That is, return the list of universal type variables with a_{1}, a_{2}, ..., a_{m} instantiated with dc_arg_{1}, dc_arg_{2}, ..., dc_arg_{m}. It is possible for m to be less than n, in which case the remaining n - m elements will simply be universal type variables (with their kinds possibly instantiated).

Examples:

• Given the data constructor D :: forall a b. Foo a b and dc_args [Int, Bool], then dataConInstUnivs D dc_args will return [Int, Bool].
• Given the data constructor D :: forall a b. Foo a b and dc_args [Int], then @dataConInstUnivs D dc_args will return [Int, b].
• Given the data constructor E :: forall k (a :: k). Bar k a and dc_args [Type], then @dataConInstUnivs D dc_args will return [Type, (a :: Type)].

This is primarily used in GHC.Tc.Deriv.* in service of instantiating data constructors' field types. See Note [Instantiating field types in stock deriving] for a notable example of this.

The labels for the fields of this particular DataCon

Extract the type for any given labelled field of the DataCon

Extract the label and type for any given labelled field of the DataCon, or return Nothing if the field does not belong to it

Strictness/unpack annotations, from user; or, for imported DataCons, from the interface file The list is in one-to-one correspondence with the arity of the DataCon

Source-level arity of the data constructor

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

Should the DataCon be presented infix?

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

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)

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)

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

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

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 data type that is all of:

• Concrete (i.e. constructors visible)
• Single-constructor
• ... which has no existentials

Whether the type is a data type or a newtype.

Return whether there are any argument types for this DataCons original source type See Note [DataCon arities]

Return whether there are any argument types for this DataCons runtime representation type See Note [DataCon arities]

Vanilla DataCons are those that are nice boring Haskell 98 constructors

Is this the DataCon of a newtype?

Were the type variables of the data con written in a different order than the regular order (universal tyvars followed by existential tyvars)?

This is not a cheap test, so we minimize its use in GHC as much as possible. Currently, its only call site in the GHC codebase is in mkDataConRep in MkId, and so dataConUserTyVarsArePermuted is only called at most once during a data constructor's lifetime.

Compare strictness annotations

Should this DataCon be allowed in a type even without -XDataKinds? Currently, only Lifted & Unlifted