ghc-9.0.2: The GHC API
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data HsSigWcTypeScoping Source #



Always bind any free tyvars of the given type, regardless of whether we have a forall at the top.

For pattern type sigs, we do want to bring those type variables into scope, even if there's a forall at the top which usually stops that happening, e.g:

\ (x :: forall a. a -> b) -> e

Here we do bring b into scope.

RULES can also use AlwaysBind, such as in the following example:

{-# RULES \"f\" forall (x :: forall a. a -> b). f x = ... b ... #-}

This only applies to RULES that do not explicitly bind their type variables. If a RULE explicitly quantifies its type variables, then NeverBind is used instead. See also Note [Pattern signature binders and scoping] in GHC.Hs.Type.


Unless there's forall at the top, do the same thing as AlwaysBind. This is only ever used in places where the "forall-or-nothing" rule is in effect. See Note [forall-or-nothing rule].


Never bind any free tyvars. This is used for RULES that have both explicit type and term variable binders, e.g.:

{-# RULES \"const\" forall a. forall (x :: a) y. const x y = x #-}

The presence of the type variable binder forall a. implies that the free variables in the types of the term variable binders x and y are not bound. In the example above, there are no such free variables, but if the user had written (y :: b) instead of y in the term variable binders, then b would be rejected for being out of scope. See also Note [Pattern signature binders and scoping] in GHC.Hs.Type.

data WarnUnusedForalls Source #

Should GHC warn if a quantified type variable goes unused? Usually, the answer is "yes", but in the particular case of binding LHsQTyVars, we avoid emitting warnings. See Note [Suppress -Wunused-foralls when binding LHsQTyVars].


Instances details
Outputable WarnUnusedForalls Source # 
Instance details

Defined in GHC.Rename.HsType

rnImplicitBndrs Source #


:: Maybe assoc

Just _ => an associated type decl

-> FreeKiTyVars

Surface-syntax free vars that we will implicitly bind. May have duplicates, which are removed here.

-> ([Name] -> RnM (a, FreeVars)) 
-> RnM (a, FreeVars) 

extractHsTyRdrTyVars :: LHsType GhcPs -> FreeKiTyVars Source #

extractHsTyRdrTyVars finds the type/kind variables of a HsType/HsKind. It's used when making the foralls explicit. See Note [Kind and type-variable binders]

extractHsTyRdrTyVarsKindVars :: LHsType GhcPs -> FreeKiTyVars Source #

Extracts the free type/kind variables from the kind signature of a HsType. This is used to implicitly quantify over k in type T = Nothing :: Maybe k. The left-to-right order of variables is preserved. See Note [Kind and type-variable binders] and Note [Ordering of implicit variables] and Note [Implicit quantification in type synonyms].

extractHsTysRdrTyVars :: [LHsType GhcPs] -> FreeKiTyVars -> FreeKiTyVars Source #

Extracts free type and kind variables from types in a list. When the same name occurs multiple times in the types, all occurrences are returned.

extractDataDefnKindVars :: HsDataDefn GhcPs -> FreeKiTyVars Source #

Get type/kind variables mentioned in the kind signature, preserving left-to-right order:

  • data T a (b :: k1) :: k2 -> k1 -> k2 -> Type -- result: [k2,k1]
  • data T a (b :: k1) -- result: []

See Note [Ordering of implicit variables].

forAllOrNothing Source #


:: Bool

True = explicit forall E.g. f :: forall a. a->b we do not want to bring b into scope, hence True But f :: a -> b we want to bring both a and b into scope, hence False

-> FreeKiTyVars

Free vars of the type

-> RnM FreeKiTyVars 

See Note [forall-or-nothing rule]. This tiny little function is used (rather than its small body inlined) to indicate that we are implementing that rule.

nubL :: Eq a => [Located a] -> [Located a] Source #