TcDerivUtils

ghc-8.4.4: The GHC API

Safe Haskell | None
Language | Haskell2010

TcDerivUtils

Synopsis

- type DerivM = ReaderT DerivEnv TcRn
- data DerivEnv = DerivEnv {
  - denv_overlap_mode :: Maybe OverlapMode
  - denv_tvs :: [TyVar]
  - denv_cls :: Class
  - denv_cls_tys :: [Type]
  - denv_tc :: TyCon
  - denv_tc_args :: [Type]
  - denv_rep_tc :: TyCon
  - denv_rep_tc_args :: [Type]
  - denv_mtheta :: DerivContext
  - denv_strat :: Maybe DerivStrategy
  }
- data DerivSpec theta = DS {
  - ds_loc :: SrcSpan
  - ds_name :: Name
  - ds_tvs :: [TyVar]
  - ds_theta :: theta
  - ds_cls :: Class
  - ds_tys :: [Type]
  - ds_tc :: TyCon
  - ds_overlap :: Maybe OverlapMode
  - ds_mechanism :: DerivSpecMechanism
  }
- pprDerivSpec :: Outputable theta => DerivSpec theta -> SDoc
- data DerivSpecMechanism
  - = DerivSpecStock (SrcSpan -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
  - | DerivSpecNewtype Type
  - | DerivSpecAnyClass
- isDerivSpecStock :: DerivSpecMechanism -> Bool
- isDerivSpecNewtype :: DerivSpecMechanism -> Bool
- isDerivSpecAnyClass :: DerivSpecMechanism -> Bool
- type DerivContext = Maybe ThetaType
- data DerivStatus
  - = CanDerive
  - | DerivableClassError SDoc
  - | DerivableViaInstance
  - | NonDerivableClass SDoc
- data PredOrigin = PredOrigin PredType CtOrigin TypeOrKind
- data ThetaOrigin = ThetaOrigin {
  - to_anyclass_skols :: [TyVar]
  - to_anyclass_metas :: [TyVar]
  - to_anyclass_givens :: ThetaType
  - to_wanted_origins :: [PredOrigin]
  }
- mkPredOrigin :: CtOrigin -> TypeOrKind -> PredType -> PredOrigin
- mkThetaOrigin :: CtOrigin -> TypeOrKind -> [TyVar] -> [TyVar] -> ThetaType -> ThetaType -> ThetaOrigin
- mkThetaOriginFromPreds :: [PredOrigin] -> ThetaOrigin
- substPredOrigin :: HasCallStack => TCvSubst -> PredOrigin -> PredOrigin
- checkSideConditions :: DynFlags -> DerivContext -> Class -> [TcType] -> TyCon -> DerivStatus
- hasStockDeriving :: Class -> Maybe (SrcSpan -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
- canDeriveAnyClass :: DynFlags -> Validity
- std_class_via_coercible :: Class -> Bool
- non_coercible_class :: Class -> Bool
- newDerivClsInst :: ThetaType -> DerivSpec theta -> TcM ClsInst
- extendLocalInstEnv :: [ClsInst] -> TcM a -> TcM a

# Documentation

type DerivM = ReaderT DerivEnv TcRn #

To avoid having to manually plumb everything in `DerivEnv` throughout various functions in `TcDeriv` and `TcDerivInfer`, we use `DerivM`, which is a simple reader around `TcRn`.

data DerivEnv #

Contains all of the information known about a derived instance when determining what its `EarlyDerivSpec` should be.

Constructors

DerivEnv |
Fields denv_overlap_mode :: Maybe OverlapMode Is this an overlapping instance? denv_tvs :: [TyVar] Universally quantified type variables in the instance denv_cls :: Class Class for which we need to derive an instance denv_cls_tys :: [Type] Other arguments to the class except the last denv_tc :: TyCon Type constructor for which the instance is requested (last arguments to the type class) denv_tc_args :: [Type] Arguments to the type constructor denv_rep_tc :: TyCon The representation tycon for `denv_tc` (for data family instances) denv_rep_tc_args :: [Type] The representation types for `denv_tc_args` (for data family instances) denv_mtheta :: DerivContext `Just` the context of the instance, for standalone deriving. `Nothing` for `deriving` clauses. denv_strat :: Maybe DerivStrategy `Just` if user requests a particular deriving strategy. Otherwise, `Nothing`.

Instances

Outputable DerivEnv # |
Instance details Defined in TcDerivUtils Methods ppr :: DerivEnv -> SDoc # pprPrec :: Rational -> DerivEnv -> SDoc #

data DerivSpec theta #

Constructors

DS |
Fields ds_loc :: SrcSpan ds_name :: Name ds_tvs :: [TyVar] ds_theta :: theta ds_cls :: Class ds_tys :: [Type] ds_tc :: TyCon ds_overlap :: Maybe OverlapMode ds_mechanism :: DerivSpecMechanism

Instances

Outputable theta => Outputable (DerivSpec theta) # |
Instance details Defined in TcDerivUtils Methods ppr :: DerivSpec theta -> SDoc # pprPrec :: Rational -> DerivSpec theta -> SDoc #

pprDerivSpec :: Outputable theta => DerivSpec theta -> SDoc #

data DerivSpecMechanism #

Constructors

DerivSpecStock (SrcSpan -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])) |
DerivSpecNewtype Type |
DerivSpecAnyClass |

Instances

Outputable DerivSpecMechanism # |
Instance details Defined in TcDerivUtils Methods ppr :: DerivSpecMechanism -> SDoc # pprPrec :: Rational -> DerivSpecMechanism -> SDoc #

isDerivSpecStock :: DerivSpecMechanism -> Bool #

isDerivSpecNewtype :: DerivSpecMechanism -> Bool #

isDerivSpecAnyClass :: DerivSpecMechanism -> Bool #

type DerivContext = Maybe ThetaType #

data DerivStatus #

Constructors

CanDerive |
DerivableClassError SDoc |
DerivableViaInstance |
NonDerivableClass SDoc |

data PredOrigin #

A `PredType` annotated with the origin of the constraint `CtOrigin`, and whether or the constraint deals in types or kinds.

Constructors

PredOrigin PredType CtOrigin TypeOrKind |

Instances

Outputable PredOrigin # |
Instance details Defined in TcDerivUtils Methods ppr :: PredOrigin -> SDoc # pprPrec :: Rational -> PredOrigin -> SDoc #

data ThetaOrigin #

A list of wanted `PredOrigin` constraints (`to_wanted_origins`) to simplify when inferring a derived instance's context. These are used in all deriving strategies, but in the particular case of `DeriveAnyClass`, we need extra information. In particular, we need:

- `to_anyclass_skols`, the list of type variables bound by a class method's regular type signature, which should be rigid.
- `to_anyclass_metas`, the list of type variables bound by a class method's default type signature. These can be unified as necessary.
- `to_anyclass_givens`, the list of constraints from a class method's regular type signature, which can be used to help solve constraints in the `to_wanted_origins`.

(Note that `to_wanted_origins` will likely contain type variables from the derived type class or data type, neither of which will appear in `to_anyclass_skols` or `to_anyclass_metas`.)

For all other deriving strategies, it is always the case that `to_anyclass_skols`, `to_anyclass_metas`, and `to_anyclass_givens` are empty.

Here is an example to illustrate this:

    class Foo a where
      bar :: forall b. Ix b => a -> b -> String
      default bar :: forall y. (Show a, Ix y) => a -> y -> String
      bar x y = show x ++ show (range (y, y))

      baz :: Eq a => a -> a -> Bool
      default baz :: Ord a => a -> a -> Bool
      baz x y = compare x y == EQ

    data Quux q = Quux deriving anyclass Foo

Then it would generate two `ThetaOrigin`s, one for each method:

    [ ThetaOrigin { to_anyclass_skols  = [b]
                  , to_anyclass_metas  = [y]
                  , to_anyclass_givens = [Ix b]
                  , to_wanted_origins  = [ Show (Quux q), Ix y
                                         , (Quux q -> b -> String) ~
                                           (Quux q -> y -> String)
                                         ] }
    , ThetaOrigin { to_anyclass_skols  = []
                  , to_anyclass_metas  = []
                  , to_anyclass_givens = [Eq (Quux q)]
                  , to_wanted_origins  = [ Ord (Quux q)
                                         , (Quux q -> Quux q -> Bool) ~
                                           (Quux q -> Quux q -> Bool)
                                         ] }
    ]

(Note that the type variable `q` is bound by the data type `Quux`, and thus it appears in neither `to_anyclass_skols` nor `to_anyclass_metas`.)

See `Note [Gathering and simplifying constraints for DeriveAnyClass]` in TcDerivInfer for an explanation of how `to_wanted_origins` are determined in `DeriveAnyClass`, as well as how `to_anyclass_skols`, `to_anyclass_metas`, and `to_anyclass_givens` are used.

Constructors

ThetaOrigin |
Fields to_anyclass_skols :: [TyVar] to_anyclass_metas :: [TyVar] to_anyclass_givens :: ThetaType to_wanted_origins :: [PredOrigin]

Instances

Outputable ThetaOrigin # |
Instance details Defined in TcDerivUtils Methods ppr :: ThetaOrigin -> SDoc # pprPrec :: Rational -> ThetaOrigin -> SDoc #

mkPredOrigin :: CtOrigin -> TypeOrKind -> PredType -> PredOrigin #

mkThetaOrigin :: CtOrigin -> TypeOrKind -> [TyVar] -> [TyVar] -> ThetaType -> ThetaType -> ThetaOrigin #

mkThetaOriginFromPreds :: [PredOrigin] -> ThetaOrigin #

substPredOrigin :: HasCallStack => TCvSubst -> PredOrigin -> PredOrigin #

checkSideConditions :: DynFlags -> DerivContext -> Class -> [TcType] -> TyCon -> DerivStatus #

hasStockDeriving :: Class -> Maybe (SrcSpan -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])) #

canDeriveAnyClass :: DynFlags -> Validity #

std_class_via_coercible :: Class -> Bool #

non_coercible_class :: Class -> Bool #

newDerivClsInst :: ThetaType -> DerivSpec theta -> TcM ClsInst #

extendLocalInstEnv :: [ClsInst] -> TcM a -> TcM a #