ghc-7.4.1: The GHC API

Safe HaskellSafe-Infered





data MetaInfo Source



tcView :: Type -> Maybe TypeSource

Similar to coreView, but for the type checker, which just looks through synonyms

repSplitAppTy_maybe :: Type -> Maybe (Type, Type)Source

Does the AppTy split as in splitAppTy_maybe, but assumes that any Core view stuff is already done

eqType :: Type -> Type -> BoolSource

Type equality on source types. Does not look through newtypes or PredTypes, but it does look through type synonyms.

shallowPredTypePredTree :: PredType -> PredTreeSource

Like classifyPredType but doesn't look through type synonyms. Used to check that programs only use simple contexts without any synonyms in them.

Finding type instances

tcTyFamInsts :: Type -> [(TyCon, [Type])]Source

Finds type family instances occuring in a type after expanding synonyms.

Finding exact (non-dead) type variables

Tidying type related things up for printing

tidyOpenType :: TidyEnv -> Type -> (TidyEnv, Type)Source

Grabs the free type variables, tidies them and then uses tidyType to work over the type itself

tidyTyVarBndr :: TidyEnv -> TyVar -> (TidyEnv, TyVar)Source

This tidies up a type for printing in an error message, or in an interface file.

It doesn't change the uniques at all, just the print names.

tidyFreeTyVars :: TidyEnv -> TyVarSet -> TidyEnvSource

Add the free TyVars to the env in tidy form, so that we can tidy the type they are free in

tidyOpenTyVar :: TidyEnv -> TyVar -> (TidyEnv, TyVar)Source

Treat a new TyVar as a binder, and give it a fresh tidy name using the environment if one has not already been allocated. See also tidyTyVarBndr

tidyTopType :: Type -> TypeSource

Calls tidyType on a top-level type (i.e. with an empty tidying environment)

type Kind = TypeSource

The key type representing kinds in the compiler. Invariant: a kind is always in one of these forms:

 FunTy k1 k2
 TyConApp PrimTyCon [...]
 TyVar kv   -- (during inference only)
 ForAll ... -- (for top-level coercions)

constraintKind, argTypeKind, openTypeKind, unliftedTypeKind, liftedTypeKind :: KindSource

See Type for details of the distinction between these Kinds

mkArrowKind :: Kind -> Kind -> KindSource

Given two kinds k1 and k2, creates the Kind k1 -> k2

mkArrowKinds :: [Kind] -> Kind -> KindSource

Iterated application of mkArrowKind

isUnliftedTypeKind :: Kind -> BoolSource

See Type for details of the distinction between these Kinds

isSubOpenTypeKind :: Kind -> BoolSource

True of any sub-kind of OpenTypeKind

True of any sub-kind of OpenTypeKind

isSubArgTypeKind :: Kind -> BoolSource

True of any sub-kind of ArgTypeKind

splitKindFunTys :: Kind -> ([Kind], Kind)Source

Essentially splitFunTys on kinds

defaultKind :: Kind -> KindSource

Used when generalising: default OpenKind and ArgKind to *. See Type for more information on what that means

data Type Source

The key representation of types within the compiler

type PredType = TypeSource

A type of the form p of kind Constraint 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"

type ThetaType = [PredType]Source

A collection of PredTypes

mkForAllTys :: [TyVar] -> Type -> TypeSource

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

mkFunTy :: Type -> Type -> TypeSource

Creates a function type from the given argument and result type

zipFunTys :: Outputable a => [a] -> Type -> ([(a, Type)], Type)Source

Splits off argument types from the given type and associating them with the things in the input list from left to right. The final result type is returned, along with the resulting pairs of objects and types, albeit with the list of pairs in reverse order. Panics if there are not enough argument types for the input list.

mkTyConApp :: TyCon -> [Type] -> TypeSource

A key function: builds a TyConApp or FunTy as apppropriate to its arguments. Applies its arguments to the constructor from left to right

mkAppTy :: Type -> Type -> TypeSource

Applies a type to another, as in e.g. k a

applyTy :: Type -> KindOrType -> TypeSource

Instantiate a forall type with one or more type arguments. Used when we have a polymorphic function applied to type args:

 f t1 t2

We use applyTys type-of-f [t1,t2] to compute the type of the expression. Panics if no application is possible.

applyTys :: Type -> [KindOrType] -> TypeSource

This function is interesting because:

  1. The function may have more for-alls than there are args
  2. Less obviously, it may have fewer for-alls

For case 2. think of:

 applyTys (forall a.a) [forall b.b, Int]

This really can happen, but only (I think) in situations involving undefined. For example: undefined :: forall a. a Term: undefined (forall b. b->b) Int This term should have type (Int -> Int), but notice that there are more type args than foralls in undefineds type.

mkTyConTy :: TyCon -> TypeSource

Create the plain type constructor type which has been applied to no type arguments at all.

mkEqPred :: (Type, Type) -> PredTypeSource

Creates a type equality predicate

data TvSubst Source

Type substitution

The following invariants must hold of a TvSubst:

  1. The in-scope set is needed only to guide the generation of fresh uniques
  2. In particular, the kind of the type variables in the in-scope set is not relevant
  3. The substition is only applied ONCE! This is because in general such application will not reached a fixed point.


type TvSubstEnv = TyVarEnv TypeSource

A substitition of Types for TyVars and Kinds for KindVars

mkOpenTvSubst :: TvSubstEnv -> TvSubstSource

Generates the in-scope set for the TvSubst from the types in the incoming environment, hence open

zipOpenTvSubst :: [TyVar] -> [Type] -> TvSubstSource

Generates the in-scope set for the TvSubst from the types in the incoming environment, hence open

mkTopTvSubst :: [(TyVar, Type)] -> TvSubstSource

Called when doing top-level substitutions. Here we expect that the free vars of the range of the substitution will be empty.

substTy :: TvSubst -> Type -> TypeSource

Substitute within a Type

substTys :: TvSubst -> [Type] -> [Type]Source

Substitute within several Types

substTyWith :: [TyVar] -> [Type] -> Type -> TypeSource

Type substitution making use of an TvSubst that is assumed to be open, see zipOpenTvSubst

isUnLiftedType :: Type -> BoolSource

See Type for what an unlifted type is

isPrimitiveType :: Type -> BoolSource

Returns true of types that are opaque to Haskell. Most of these are unlifted, but now that we interact with .NET, we may have primtive (foreign-imported) types that are lifted

tyVarsOfType :: Type -> VarSetSource

NB: for type synonyms tyVarsOfType does not expand the synonym tyVarsOfType returns only the free *type* variables of a type For example, tyVarsOfType (a::k) returns {a}, not including the kind variable {k}