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{-
Describes predicates as they are considered by the solver.
-}
module Predicate (
Pred(..), classifyPredType,
isPredTy, isEvVarType,
-- Equality predicates
EqRel(..), eqRelRole,
isEqPrimPred, isEqPred,
getEqPredTys, getEqPredTys_maybe, getEqPredRole,
predTypeEqRel,
mkPrimEqPred, mkReprPrimEqPred, mkPrimEqPredRole,
mkHeteroPrimEqPred, mkHeteroReprPrimEqPred,
-- Class predicates
mkClassPred, isDictTy,
isClassPred, isEqPredClass, isCTupleClass,
getClassPredTys, getClassPredTys_maybe,
-- Implicit parameters
isIPPred, isIPPred_maybe, isIPTyCon, isIPClass, hasIPPred,
-- Evidence variables
DictId, isEvVar, isDictId
) where
import GhcPrelude
import Type
import Class
import TyCon
import Var
import Coercion
import PrelNames
import FastString
import Outputable
import Util
import Control.Monad ( guard )
-- | A predicate in the solver. The solver tries to prove Wanted predicates
-- from Given ones.
data Pred
= ClassPred Class [Type]
| EqPred EqRel Type Type
| IrredPred PredType
| ForAllPred [TyCoVarBinder] [PredType] PredType
-- ForAllPred: see Note [Quantified constraints] in TcCanonical
-- NB: There is no TuplePred case
-- Tuple predicates like (Eq a, Ord b) are just treated
-- as ClassPred, as if we had a tuple class with two superclasses
-- class (c1, c2) => (%,%) c1 c2
classifyPredType :: PredType -> Pred
classifyPredType ev_ty = case splitTyConApp_maybe ev_ty of
Just (tc, [_, _, ty1, ty2])
| tc `hasKey` eqReprPrimTyConKey -> EqPred ReprEq ty1 ty2
| tc `hasKey` eqPrimTyConKey -> EqPred NomEq ty1 ty2
Just (tc, tys)
| Just clas <- tyConClass_maybe tc
-> ClassPred clas tys
_ | (tvs, rho) <- splitForAllVarBndrs ev_ty
, (theta, pred) <- splitFunTys rho
, not (null tvs && null theta)
-> ForAllPred tvs theta pred
| otherwise
-> IrredPred ev_ty
-- --------------------- Dictionary types ---------------------------------
mkClassPred :: Class -> [Type] -> PredType
mkClassPred clas tys = mkTyConApp (classTyCon clas) tys
isDictTy :: Type -> Bool
isDictTy = isClassPred
getClassPredTys :: HasDebugCallStack => PredType -> (Class, [Type])
getClassPredTys ty = case getClassPredTys_maybe ty of
Just (clas, tys) -> (clas, tys)
Nothing -> pprPanic "getClassPredTys" (ppr ty)
getClassPredTys_maybe :: PredType -> Maybe (Class, [Type])
getClassPredTys_maybe ty = case splitTyConApp_maybe ty of
Just (tc, tys) | Just clas <- tyConClass_maybe tc -> Just (clas, tys)
_ -> Nothing
-- --------------------- Equality predicates ---------------------------------
-- | A choice of equality relation. This is separate from the type 'Role'
-- because 'Phantom' does not define a (non-trivial) equality relation.
data EqRel = NomEq | ReprEq
deriving (Eq, Ord)
instance Outputable EqRel where
ppr NomEq = text "nominal equality"
ppr ReprEq = text "representational equality"
eqRelRole :: EqRel -> Role
eqRelRole NomEq = Nominal
eqRelRole ReprEq = Representational
getEqPredTys :: PredType -> (Type, Type)
getEqPredTys ty
= case splitTyConApp_maybe ty of
Just (tc, [_, _, ty1, ty2])
| tc `hasKey` eqPrimTyConKey
|| tc `hasKey` eqReprPrimTyConKey
-> (ty1, ty2)
_ -> pprPanic "getEqPredTys" (ppr ty)
getEqPredTys_maybe :: PredType -> Maybe (Role, Type, Type)
getEqPredTys_maybe ty
= case splitTyConApp_maybe ty of
Just (tc, [_, _, ty1, ty2])
| tc `hasKey` eqPrimTyConKey -> Just (Nominal, ty1, ty2)
| tc `hasKey` eqReprPrimTyConKey -> Just (Representational, ty1, ty2)
_ -> Nothing
getEqPredRole :: PredType -> Role
getEqPredRole ty = eqRelRole (predTypeEqRel ty)
-- | Get the equality relation relevant for a pred type.
predTypeEqRel :: PredType -> EqRel
predTypeEqRel ty
| Just (tc, _) <- splitTyConApp_maybe ty
, tc `hasKey` eqReprPrimTyConKey
= ReprEq
| otherwise
= NomEq
{-------------------------------------------
Predicates on PredType
--------------------------------------------}
{-
Note [Evidence for quantified constraints]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The superclass mechanism in TcCanonical.makeSuperClasses risks
taking a quantified constraint like
(forall a. C a => a ~ b)
and generate superclass evidence
(forall a. C a => a ~# b)
This is a funny thing: neither isPredTy nor isCoVarType are true
of it. So we are careful not to generate it in the first place:
see Note [Equality superclasses in quantified constraints]
in TcCanonical.
-}
isEvVarType :: Type -> Bool
-- True of (a) predicates, of kind Constraint, such as (Eq a), and (a ~ b)
-- (b) coercion types, such as (t1 ~# t2) or (t1 ~R# t2)
-- See Note [Types for coercions, predicates, and evidence] in TyCoRep
-- See Note [Evidence for quantified constraints]
isEvVarType ty = isCoVarType ty || isPredTy ty
isEqPredClass :: Class -> Bool
-- True of (~) and (~~)
isEqPredClass cls = cls `hasKey` eqTyConKey
|| cls `hasKey` heqTyConKey
isClassPred, isEqPred, isEqPrimPred, isIPPred :: PredType -> Bool
isClassPred ty = case tyConAppTyCon_maybe ty of
Just tyCon | isClassTyCon tyCon -> True
_ -> False
isEqPred ty -- True of (a ~ b) and (a ~~ b)
-- ToDo: should we check saturation?
| Just tc <- tyConAppTyCon_maybe ty
, Just cls <- tyConClass_maybe tc
= isEqPredClass cls
| otherwise
= False
isEqPrimPred ty = isCoVarType ty
-- True of (a ~# b) (a ~R# b)
isIPPred ty = case tyConAppTyCon_maybe ty of
Just tc -> isIPTyCon tc
_ -> False
isIPTyCon :: TyCon -> Bool
isIPTyCon tc = tc `hasKey` ipClassKey
-- Class and its corresponding TyCon have the same Unique
isIPClass :: Class -> Bool
isIPClass cls = cls `hasKey` ipClassKey
isCTupleClass :: Class -> Bool
isCTupleClass cls = isTupleTyCon (classTyCon cls)
isIPPred_maybe :: Type -> Maybe (FastString, Type)
isIPPred_maybe ty =
do (tc,[t1,t2]) <- splitTyConApp_maybe ty
guard (isIPTyCon tc)
x <- isStrLitTy t1
return (x,t2)
hasIPPred :: PredType -> Bool
hasIPPred pred
= case classifyPredType pred of
ClassPred cls tys
| isIPClass cls -> True
| isCTupleClass cls -> any hasIPPred tys
_other -> False
{-
************************************************************************
* *
Evidence variables
* *
************************************************************************
-}
isEvVar :: Var -> Bool
isEvVar var = isEvVarType (varType var)
isDictId :: Id -> Bool
isDictId id = isDictTy (varType id)
|
