GHC.Core.Type

Attempts to obtain the type variable underlying a Type, and panics with the given message if this is not a type variable type. See also getTyVar_maybe

Attempts to obtain the type variable underlying a Type

Attempts to obtain the type variable underlying a Type, without any expansion

If the type is a tyvar, possibly under a cast, returns it, along with the coercion. Thus, the co is :: kind tv ~N kind ty

The type or kind of the Var in question

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

Attempts to take a type application apart, as in splitAppTy_maybe, and panics if this is not possible

Recursively splits a type as far as is possible, leaving a residual type being applied to and the type arguments applied to it. Never fails, even if that means returning an empty list of type applications.

Like splitAppTys, but doesn't look through type synonyms

Attempt to take a type application apart, whether it is a function, type constructor, or plain type application. Note that type family applications are NEVER unsaturated by this!

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

Just like splitAppTyNoView_maybe, but does not split (c => t).

See Note [Decomposing fat arrow c=>t]

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

Attempts to extract the multiplicity, argument and result types from a type, and panics if that is not possible. See also splitFunTy_maybe

Attempts to extract the multiplicity, argument and result types from a type

Works on visible function types only (t1 -> t2), and returns t1 and t2, but not the multiplicity

Extract the function result type and panic if that is not possible

Extract the function argument type and panic if that is not possible

Just like piResultTys but for a single argument Try not to iterate piResultTy, because it's inefficient to substitute one variable at a time; instead use 'piResultTys"

Given the components of a FunTy figure out the corresponding TyConApp.

Return Just if this TyConApp should be represented as a FunTy

Return Just if this TyConAppCo should be represented as a FunCo

This one works out the FunTyFlag from the argument type See GHC.Types.Var Note [FunTyFlag]

Like mkFunctionType, compute the FunTyFlag from the arguments

See GHC.Types.Var Note [FunTyFlag]

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

(mkTyConTy tc) returns (TyConApp tc []) but arranges to share that TyConApp among all calls See Note [Sharing nullary TyConApps] So it's just an alias for tyConNullaryTy!

The same as fst . splitTyConApp We can short-cut the FunTy case

Retrieve the tycon heading this type, if there is one. Does not look through synonyms.

The same as snd . splitTyConApp

Attempts to tease a type apart into a type constructor and the application of a number of arguments to that constructor

Attempts to tease a type apart into a type constructor and the application of a number of arguments to that constructor. Panics if that is not possible. See also splitTyConApp_maybe

tcSplitTyConApp_maybe splits a type constructor application into its type constructor and applied types.

Differs from splitTyConApp_maybe in that it does *not* split types headed with (=>), as that's not a TyCon in the type-checker.

Note that this may fail (in funTyConAppTy_maybe) in the case of a FunTy with an argument of unknown kind FunTy (e.g. `FunTy (a :: k) Int`, since the kind of a isn't of the form `TYPE rep`. This isn't usually a problem but may be temporarily the case during canonicalization: see Note [Decomposing FunTy] in GHC.Tc.Solver.Equality and Note [The Purely Kinded Type Invariant (PKTI)] in GHC.Tc.Gen.HsType, Wrinkle around FunTy

Consequently, you may need to zonk your type before using this function.

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

Like mkForAllTys, but assumes all variables are dependent and Inferred, a common case

Like mkForAllTy, but assumes the variable is dependent and Specified, a common case

Like mkForAllTys, but assumes all variables are dependent and Specified, a common case

Like mkForAllTys, but assumes all variables are dependent and visible

Make a dependent forall over a TyCoVar

Make a dependent forall over a TyCoVar

Make a dependent forall over an Inferred variable

Like mkTyCoInvForAllTy, but tv should be a tyvar

Like mkTyCoInvForAllTys, but tvs should be a list of tyvar

Take a ForAllTy apart, returning the list of tycovars and the result type. This always succeeds, even if it returns only an empty list. Note that the result type returned may have free variables that were bound by a forall.

Like splitForAllTyCoVars, but split only for tyvars. This always succeeds, even if it returns only an empty list. Note that the result type returned may have free variables that were bound by a forall.

Like splitForAllTyCoVars, but only splits ForAllTys with Required type variable binders. Furthermore, each returned tyvar is annotated with ().

Like splitForAllTyCoVars, but only splits ForAllTys with Invisible type variable binders. Furthermore, each returned tyvar is annotated with its Specificity.

Take a ForAllTy apart, returning the binders and result type

Attempts to take a ForAllTy apart, returning the full ForAllTyBinder

Attempts to take a ForAllTy apart, returning the Var

Take a forall type apart, or panics if that is not possible.

Attempts to take a ForAllTy apart, but only if the binder is a TyVar

Like splitForAllTyCoVar_maybe, but only returns Just if it is a covar binder.

Attempts to take a forall type apart; works with proper foralls and functions

Takes a forall type apart, or panics

Split off all PiTyBinders to a type, splitting both proper foralls and functions

Extracts a list of run-time arguments from a function type, looking through newtypes to the right of arrows.

Examples:

   newtype Identity a = I a

   getRuntimeArgTys (Int -> Bool -> Double) == [(Int, FTF_T_T), (Bool, FTF_T_T)]
   getRuntimeArgTys (Identity Int -> Bool -> Double) == [(Identity Int, FTF_T_T), (Bool, FTF_T_T)]
   getRuntimeArgTys (Int -> Identity (Bool -> Identity Double)) == [(Int, FTF_T_T), (Bool, FTF_T_T)]
   getRuntimeArgTys (forall a. Show a => Identity a -> a -> Int -> Bool)
            == [(Show a, FTF_C_T), (Identity a, FTF_T_T),(a, FTF_T_T),(Int, FTF_T_T)]

Note that, in the last case, the returned types might mention an out-of-scope type variable. This function is used only when we really care about the kinds of the returned types, so this is OK.

• *Warning**: this function can return an infinite list. For example:

  newtype N a = MkN (a -> N a)
  getRuntimeArgTys (N a) == repeat (a, FTF_T_T)

Given a list of type-level vars and the free vars of a result kind, makes PiTyBinders, preferring anonymous binders if the variable is, in fact, not dependent. e.g. mkTyConBindersPreferAnon (k:*),(b:k),(c:k) We want (k:*) Named, (b:k) Anon, (c:k) Anon

All non-coercion binders are visible.

(piResultTys f_ty [ty1, .., tyn]) gives the type of (f ty1 .. tyn) where f :: f_ty piResultTys is interesting because: 1. f_ty may have more for-alls than there are args 2. Less obviously, it may have fewer for-alls For case 2. think of: piResultTys (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.

Drops all ForAllTys

Given a family instance TyCon and its arg types, return the corresponding family type. E.g:

data family T a
data instance T (Maybe b) = MkT b

Where the instance tycon is :RTL, so:

mkFamilyTyConApp :RTL Int  =  T (Maybe Int)

Is this a numeric literal. We also look through type synonyms.

Is this a symbol literal. We also look through type synonyms.

Is this a char literal? We also look through type synonyms.

Is this a type literal (symbol, numeric, or char)?

Extract the RuntimeRep classifier of a type. For instance, getRuntimeRep_maybe Int = LiftedRep. Panics if this is not possible.

(splitRuntimeRep_maybe rr) takes a Type rr :: RuntimeRep, and returns the (TyCon,[Type]) for the RuntimeRep, if possible, where the TyCon is one of the promoted DataCons of RuntimeRep. Remember: the unique on TyCon that is a a promoted DataCon is the same as the unique on the DataCon See Note [Promoted data constructors] in GHC.Core.TyCon May not be possible if rr is a type variable or type family application

Given a kind (TYPE rr) or (CONSTRAINT rr), extract its RuntimeRep classifier rr. For example, kindRep_maybe * = Just LiftedRep Returns Nothing if the kind is not of form (TYPE rr)

Extract the RuntimeRep classifier of a type from its kind. For example, kindRep * = LiftedRep; Panics if this is not possible. Treats * and Constraint as the same

Extract the Levity of a type. For example, getLevity Int = Lifted, or getLevity (Array# Int) = Unlifted.

Panics if this is not possible. Does not look through type family applications.

levityType_maybe takes a Type of kind Levity, and returns its levity May not be possible for a type variable or type family application

Make a CastTy. The Coercion must be nominal. Checks the Coercion for reflexivity, dropping it if it's reflexive. See Note [Respecting definitional equality] in GHC.Core.TyCo.Rep

A type of kind ErrorMessage (from the GHC.TypeError module).

Render a type corresponding to a user type error into a SDoc.

Get the type on the LHS of a coercion induced by a type/data family instance.

Like splitPiTys, but returns only *invisible* binders, including constraints. Stops at the first visible binder.

Same as splitInvisPiTys, but stop when - you have found n PiTyBinders, - or you run out of invisible binders

Given a TyCon and a list of argument types, filter out any invisible (i.e., Inferred or Specified) arguments.

Given a TyCon and a list of argument types, filter out any Inferred arguments.

Given a TyCon and a list of argument types, partition the arguments into:

1. Inferred or Specified (i.e., invisible) arguments and

2. Required (i.e., visible) arguments

Given a list of things paired with their visibilities, partition the things into (invisible things, visible things).

Given a TyCon and a list of argument types to which the TyCon is applied, determine each argument's visibility (Inferred, Specified, or Required).

Wrinkle: consider the following scenario:

T :: forall k. k -> k
tyConForAllTyFlags T [forall m. m -> m -> m, S, R, Q]

After substituting, we get

T (forall m. m -> m -> m) :: (forall m. m -> m -> m) -> forall n. n -> n -> n

Thus, the first argument is invisible, S is visible, R is invisible again, and Q is visible.

Given a Type and a list of argument types to which the Type is applied, determine each argument's visibility (Inferred, Specified, or Required).

Most of the time, the arguments will be Required, but not always. Consider f :: forall a. a -> Type. In f Type Bool, the first argument (Type) is Specified and the second argument (Bool) is Required. It is precisely this sort of higher-rank situation in which appTyForAllTyFlags comes in handy, since f Type Bool would be represented in Core using AppTys. (See also #15792).

This describes how a "map" operation over a type/coercion should behave

A view function that looks through nothing.

Unwrap one layer of newtype on a type constructor and its arguments, using an eta-reduced version of the newtype if possible. This requires tys to have at least newTyConInstArity tycon elements.

Make a named binder

Make many named binders

Make a named binder var should be a type variable

Make many named binders Input vars should be type variables

Does this binder bind a variable that is not erased? Returns True for anonymous binders.

Extract a relevant type, if there is one.

Does this ForAllTyFlag classify an argument that is written in Haskell?

Does this ForAllTyFlag classify an argument that is not written in Haskell?

Does this binder bind a visible argument?

Does this binder bind an invisible argument?

Is this type a function type (e.g. X -> Y or X => Y), after expanding type synonyms?

Note:

• Does not look through newtypes, so isFunTy is False for IO (), despite the latter being operationally a function (after expanding newtypes).

• Does not reduce type family applications, so isFunTy is False for Id (Int -> Bool) (where Id is the identity type family).

• Does not consider ForAllTy to be a function type (even when the argument is a required argument), nor does it look through foralls. Hence both isFunTy is False for both forall b. Show b => b -> b and for forall a -> Int.

See also mightBeFunTy, when you want to know whether something could be a function (taking a value argument) at runtime.

Checks whether this is a proper forall (with a named binder)

Like isForAllTy, but returns True only if it is a tyvar binder

Like isForAllTy, but returns True only if it is a covar binder

Like isForAllTy, but returns True only if it is an inferred tyvar binder

Is this type a FunTy or a ForAllTy, after expanding type synonyms?

Does not look through newtypes nor reduce type family applications.

Determine whether a type could be the type of a join point of given total arity, according to the polymorphism rule. A join point cannot be polymorphic in its return type, since given join j a b x y z = e1 in e2, the types of e1 and e2 must be the same, and a and b are not in scope for e2. (See Note [The polymorphism rule of join points] in GHC.Core.) Returns False also if the type simply doesn't have enough arguments.

Note that we need to know how many arguments (type *and* value) the putative join point takes; for instance, if j :: forall a. a -> Int then j could be a binary join point returning an Int, but it could *not* be a unary join point returning a -> Int.

TODO: See Note [Excess polymorphism and join points]

Does a TyCon (that is applied to some number of arguments) need to be ascribed with an explicit kind signature to resolve ambiguity if rendered as a source-syntax type? (See Note [When does a tycon application need an explicit kind signature?] for a full explanation of what this function checks for.)

Tries to compute the Levity of the given type. Returns either a definite Levity, or Nothing if we aren't sure (e.g. the type is representation-polymorphic).

Panics if the kind does not have the shape TYPE r.

Returns True if the argument is (lifted) Type or Constraint See Note [TYPE and CONSTRAINT] in GHC.Builtin.Types.Prim

Returns True if the kind classifies unlifted types (like Int#) and False otherwise. Note that this returns False for representation-polymorphic kinds, which may be specialized to a kind that classifies unlifted types.

Check whether a type of kind RuntimeRep is lifted.

isLiftedRuntimeRep is:

• True of LiftedRep :: RuntimeRep

• False of type variables, type family applications, and of other reps such as IntRep :: RuntimeRep.

Check whether a type of kind RuntimeRep is unlifted.

• True of definitely unlifted RuntimeReps such as UnliftedRep, IntRep, FloatRep, ...

• False of LiftedRep,

• False for type variables and type family applications.

Check whether a type (usually of kind RuntimeRep) is lifted, unlifted, or unknown. Returns Nothing if the type isn't of kind RuntimeRep.

`runtimeRepLevity_maybe rr` returns:

• `Just Lifted` if rr is `LiftedRep :: RuntimeRep`

• `Just Unlifted` if rr is definitely unlifted, e.g. IntRep

• Nothing if not known (e.g. it's a type variable or a type family application).

See isBoxedRuntimeRep_maybe.

Is the given type definitely unlifted? See Type#type_classification for what an unlifted type is.

Panics on representation-polymorphic types; See mightBeUnliftedType for a more approximate predicate that behaves better in the presence of representation polymorphism.

See Type#type_classification for what a boxed type is. Panics on representation-polymorphic types; See mightBeUnliftedType for a more approximate predicate that behaves better in the presence of representation polymorphism.

Check whether a kind is of the form `TYPE (BoxedRep Lifted)` or `TYPE (BoxedRep Unlifted)`.

Returns:

• `Just Lifted` for `TYPE (BoxedRep Lifted)` and Type,

• `Just Unlifted` for `TYPE (BoxedRep Unlifted)` and UnliftedType,

• Nothing for anything else, e.g. `TYPE IntRep`, `TYPE (BoxedRep l)`, etc.

Returns:

• False if the type is guaranteed unlifted or

• True if it lifted, OR we aren't sure (e.g. in a representation-polymorphic case)

Returns:

• False if the type is guaranteed lifted or

• True if it is unlifted, OR we aren't sure (e.g. in a representation-polymorphic case)

See Type#type_classification for what an algebraic type is. Should only be applied to types, as opposed to e.g. partially saturated type constructors

Check whether a type is a data family type

Returns true of types that are opaque to Haskell.

Computes whether an argument (or let right hand side) should be computed strictly or lazily, based only on its type. Currently, it's just isUnliftedType. Panics on representation-polymorphic types.

True = a term of this type cannot be bottom This identifies the types described by Note [NON-BOTTOM-DICTS invariant] in GHC.Core NB: unlifted types are not terminating types! e.g. you can write a term (loop 1)::Int# that diverges.

Is this the type Levity?

Is a tyvar of type Levity?

Is this the type RuntimeRep?

Is a tyvar of type RuntimeRep?

Is this a type of kind RuntimeRep? (e.g. LiftedRep)

Drops prefix of RuntimeRep constructors in TyConApps. Useful for e.g. dropping 'LiftedRep arguments of unboxed tuple TyCon applications:

dropRuntimeRepArgs [ 'LiftedRep, 'IntRep , String, Int# ] == [String, Int#]

Returns True if a type has a syntactically fixed runtime rep, as per Note [Fixed RuntimeRep] in GHC.Tc.Utils.Concrete.

This function is equivalent to `isFixedRuntimeRepKind . typeKind` but much faster.

Precondition: The type has kind (TYPE blah)

Is this kind equivalent to Type i.e. TYPE LiftedRep?

Is this kind equivalent to TYPE (BoxedRep l) for some l :: Levity?

Is this kind equivalent to TYPE r (for some unknown r)?

This considers Constraint to be distinct from *.

Add the kind variables free in the kinds of the tyvars in the given set. Returns a deterministic set.

Generates the in-scope set for the Subst from the types in the incoming environment. No CoVars or Ids, please!

Generates the in-scope set for the TCvSubst from the types in the incoming environment. No CoVars, please! The InScopeSet is just a thunk so with a bit of luck it'll never be evaluated

Remove all substitutions that might have been built up while preserving the in-scope set originally called zapSubstEnv

Find the in-scope set: see Note [The substitution invariant]

Returns the deep free variables of the types in the range of a substitution as a non-deterministic set.

Add the Var to the in-scope set

Add the Vars to the in-scope set: see also extendInScope

Add the Vars to the in-scope set: see also extendInScope

Add a substitution from a CoVar to a Coercion to the Subst: you must ensure that the in-scope set satisfies Note [The substitution invariant] after extending the substitution like this

Add a substitution for a TyVar to the Subst The TyVar *must* be a real TyVar, and not a CoVar You must ensure that the in-scope set is such that Note [The substitution invariant] holds after extending the substitution like this.

Adds multiple TyVar substitutions to the Subst: see also extendTvSubst

Composes two substitutions, applying the second one provided first, like in function composition. This function leaves IdSubstEnv untouched because IdSubstEnv is not used during substitution for types.

The InScopeSet is just a thunk so with a bit of luck it'll never be evaluated

Checks whether the tyvar and covar environments are empty. This function should be used over isEmptySubst when substituting for types, because types currently do not contain expressions; we can safely disregard the expression environment when deciding whether to skip a substitution. Using isEmptyTCvSubst gives us a non-trivial performance boost (up to 70% less allocation for T18223)

Substitute within a Type The substitution has to satisfy the invariants described in Note [The substitution invariant].

Substitute within several Types The substitution has to satisfy the invariants described in Note [The substitution invariant].

Type substitution, see zipTvSubst

Type substitution, see zipTvSubst

Substitute within a ThetaType The substitution has to satisfy the invariants described in Note [The substitution invariant].

Substitute within a Type after adding the free variables of the type to the in-scope set. This is useful for the case when the free variables aren't already in the in-scope set or easily available. See also Note [The substitution invariant].

Substitute within a Type disabling the sanity checks. The problems that the sanity checks in substTy catch are described in Note [The substitution invariant]. The goal of #11371 is to migrate all the calls of substTyUnchecked to substTy and remove this function. Please don't use in new code.

Substitute within several Types disabling the sanity checks. The problems that the sanity checks in substTys catch are described in Note [The substitution invariant]. The goal of #11371 is to migrate all the calls of substTysUnchecked to substTys and remove this function. Please don't use in new code.

Substitute within a ThetaType disabling the sanity checks. The problems that the sanity checks in substTys catch are described in Note [The substitution invariant]. The goal of #11371 is to migrate all the calls of substThetaUnchecked to substTheta and remove this function. Please don't use in new code.

Type substitution, see zipTvSubst. Disables sanity checks. The problems that the sanity checks in substTy catch are described in Note [The substitution invariant]. The goal of #11371 is to migrate all the calls of substTyUnchecked to substTy and remove this function. Please don't use in new code.

Substitute within a Coercion The substitution has to satisfy the invariants described in Note [The substitution invariant].

Coercion substitution, see zipTvSubst