GHC.Core.TyCo.Rep

The key representation of types within the compiler

The key type representing kinds in the compiler.

Type synonym used for types of kind RuntimeRep.

Type synonym used for types of kind Levity.

A type labeled KnotTied might have knot-tied tycons in it. See Note [Type checking recursive type and class declarations] in GHC.Tc.TyCl

A type of the form p of constraint kind represents a value whose type is the Haskell predicate p, where a predicate is what occurs before the => in a Haskell type.

We use PredType as documentation to mark those types that we guarantee to have this kind.

It can be expanded into its representation, but:

• The type checker must treat it as opaque

• The rest of the compiler treats it as transparent

Consider these examples:

f :: (Eq a) => a -> Int
g :: (?x :: Int -> Int) => a -> Int
h :: (r\l) => {r} => {l::Int | r}

Here the Eq a and ?x :: Int -> Int and rl are all called "predicates"

A collection of PredTypes

ForAllTyFlag

Is something required to appear in source Haskell (Required), permitted by request (Specified) (visible type application), or prohibited entirely from appearing in source Haskell (Inferred)? See Note [VarBndrs, ForAllTyBinders, TyConBinders, and visibility] in GHC.Core.TyCo.Rep

The non-dependent version of ForAllTyFlag. See Note [FunTyFlag] Appears here partly so that it's together with its friends ForAllTyFlag and ForallVisFlag, but also because it is used in IfaceType, rather early in the compilation chain

A Coercion is concrete evidence of the equality/convertibility of two types.

For simplicity, we have just one UnivCo that represents a coercion from some type to some other type, with (in general) no restrictions on the type. The UnivCoProvenance specifies more exactly what the coercion really is and why a program should (or shouldn't!) trust the coercion. It is reasonable to consider each constructor of UnivCoProvenance as a totally independent coercion form; their only commonality is that they don't tell you what types they coercion between. (That info is in the UnivCo constructor of Coercion.

A coercion to be filled in by the type-checker. See Note [Coercion holes]

A semantically more meaningful type to represent what may or may not be a useful Coercion.

A CoHoleSet stores a set of CoercionHoles that have been used to rewrite a constraint. See Note [Wanteds rewrite Wanteds: rewriter-sets] in GHC.Tc.Types.Constraint

mkNakedTyConTy creates a nullary TyConApp. In general you should rather use GHC.Core.Type.mkTyConTy, which picks the shared nullary TyConApp from inside the TyCon (via tyConNullaryTy. But we have to build the TyConApp tc [] in that TyCon field; that's what mkNakedTyConTy is for.

Like mkTyCoForAllTy, but does not check the occurrence of the binder See Note [Unused coercion variable in ForAllTy]

Wraps foralls over the type using the provided TyCoVars from left to right

Wraps foralls over the type using the provided InvisTVBinders from left to right

Make nested arrow types | Special, common, case: Arrow type with mult Many

A shorthand for data with an attached Mult element (the multiplicity).

Apply a function to both the Mult and the Type in a 'Scaled Type'

Mult is a type alias for Type.

Mult must contain Type because multiplicity variables are mere type variables (of kind Multiplicity) in Haskell. So the simplest implementation is to make Mult be Type.

Multiplicities can be formed with: - One: GHC.Types.One (= oneDataCon) - Many: GHC.Types.Many (= manyDataCon) - Multiplication: GHC.Types.MultMul (= multMulTyCon)

So that Mult feels a bit more structured, we provide pattern synonyms and smart constructors for these.