ghc-8.2.1: The GHC API

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type FamInstEnv = UniqDFM FamilyInstEnv Source #


mkNewTypeCoAxiom :: Name -> TyCon -> [TyVar] -> [Role] -> Type -> CoAxiom Unbranched Source #

Create a coercion constructor (axiom) suitable for the given newtype TyCon. The Name should be that of a new coercion CoAxiom, the TyVars the arguments expected by the newtype and the type the appropriate right hand side of the newtype, with the free variables a subset of those TyVars.

apartnessCheck Source #


:: [Type]

flattened target arguments. Make sure they're flattened! See Note [Flattening]. (NB: This "flat" is a different "flat" than is used in TcFlatten.)

-> CoAxBranch

the candidate equation we wish to use Precondition: this matches the target

-> Bool

True = equation can fire

Do an apartness check, as described in the "Closed Type Families" paper (POPL '14). This should be used when determining if an equation (CoAxBranch) of a closed type family can be used to reduce a certain target type family application.

data InjectivityCheckResult Source #

Result of testing two type family equations for injectiviy.



Either RHSs are distinct or unification of RHSs leads to unification of LHSs

InjectivityUnified CoAxBranch CoAxBranch

RHSs unify but LHSs don't unify under that substitution. Relevant for closed type families where equation after unification might be overlpapped (in which case it is OK if they don't unify). Constructor stores axioms after unification.

lookupFamInstEnvInjectivityConflicts :: [Bool] -> FamInstEnvs -> FamInst -> [CoAxBranch] Source #

Check whether an open type family equation can be added to already existing instance environment without causing conflicts with supplied injectivity annotations. Returns list of conflicting axioms (type instance declarations).

injectiveBranches :: [Bool] -> CoAxBranch -> CoAxBranch -> InjectivityCheckResult Source #

Check whether two type family axioms don't violate injectivity annotation.

topNormaliseType_maybe :: FamInstEnvs -> Type -> Maybe (Coercion, Type) Source #

Get rid of *outermost* (or toplevel) * type function redex * data family redex * newtypes returning an appropriate Representational coercion. Specifically, if topNormaliseType_maybe env ty = Just (co, ty') then (a) co :: ty ~R ty' (b) ty' is not a newtype, and is not a type-family or data-family redex

However, ty' can be something like (Maybe (F ty)), where (F ty) is a redex.

pmTopNormaliseType_maybe :: FamInstEnvs -> Type -> Maybe (Type, [DataCon], Type) Source #

Get rid of *outermost* (or toplevel) * type function redex * data family redex * newtypes

Behaves exactly like topNormaliseType_maybe, but instead of returning a coercion, it returns useful information for issuing pattern matching warnings. See Note [Type normalisation for EmptyCase] for details.