TcDerivUtils

ghc-8.6.3: 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_ctxt :: DerivContext
  - denv_strat :: Maybe (DerivStrategy GhcTc)
  }
- 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_standalone_wildcard :: Maybe SrcSpan
  - ds_mechanism :: DerivSpecMechanism
  }
- pprDerivSpec :: Outputable theta => DerivSpec theta -> SDoc
- data DerivSpecMechanism
  - = DerivSpecStock (SrcSpan -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
  - | DerivSpecNewtype Type
  - | DerivSpecAnyClass
  - | DerivSpecVia Type
- derivSpecMechanismToStrategy :: DerivSpecMechanism -> DerivStrategy GhcTc
- isDerivSpecStock :: DerivSpecMechanism -> Bool
- isDerivSpecNewtype :: DerivSpecMechanism -> Bool
- isDerivSpecAnyClass :: DerivSpecMechanism -> Bool
- isDerivSpecVia :: DerivSpecMechanism -> Bool
- data DerivContext
  - = InferContext (Maybe SrcSpan)
  - | SupplyContext ThetaType
- data OriginativeDerivStatus
  - = CanDeriveStock (SrcSpan -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
  - | StockClassError SDoc
  - | CanDeriveAnyClass
  - | NonDerivableClass SDoc
- isStandaloneDeriv :: DerivM Bool
- isStandaloneWildcardDeriv :: DerivM Bool
- mkDerivOrigin :: Bool -> CtOrigin
- 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
- checkOriginativeSideConditions :: DynFlags -> DerivContext -> Class -> [TcType] -> TyCon -> TyCon -> OriginativeDerivStatus
- 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_ctxt :: DerivContext ``SupplyContext` theta` for standalone deriving (where `theta` is the context of the instance). `InferContext` for `deriving` clauses, or for standalone deriving that uses a wildcard constraint. See `Note [Inferring the instance context]`. denv_strat :: Maybe (DerivStrategy GhcTc) `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_standalone_wildcard :: Maybe SrcSpan 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 |
DerivSpecVia Type |

Instances

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

derivSpecMechanismToStrategy :: DerivSpecMechanism -> DerivStrategy GhcTc #

Convert a `DerivSpecMechanism` to its corresponding `DerivStrategy`.

isDerivSpecStock :: DerivSpecMechanism -> Bool #

isDerivSpecNewtype :: DerivSpecMechanism -> Bool #

isDerivSpecAnyClass :: DerivSpecMechanism -> Bool #

isDerivSpecVia :: DerivSpecMechanism -> Bool #

data DerivContext #

Whether GHC is processing a `deriving` clause or a standalone deriving declaration.

Constructors

InferContext (Maybe SrcSpan) | `'InferContext mb_wildcard` is either: A `deriving` clause (in which case `mb_wildcard` is `Nothing`). A standalone deriving declaration with an extra-constraints wildcard as the context (in which case `mb_wildcard` is ``Just` loc`, where `loc` is the location of the wildcard. GHC should infer the context.
SupplyContext ThetaType | ``SupplyContext` theta` is a standalone deriving declaration, where `theta` is the context supplied by the user.

Instances

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

data OriginativeDerivStatus #

Records whether a particular class can be derived by way of an originative deriving strategy (i.e., `stock` or `anyclass`).

See `Note [Deriving strategies]` in TcDeriv.

Constructors

CanDeriveStock (SrcSpan -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])) |
StockClassError SDoc |
CanDeriveAnyClass |
NonDerivableClass SDoc |

isStandaloneDeriv :: DerivM Bool #

Is GHC processing a stanalone deriving declaration?

isStandaloneWildcardDeriv :: DerivM Bool #

Is GHC processing a standalone deriving declaration with an extra-constraints wildcard as the context? (e.g., `deriving instance _ => Eq (Foo a)`)

mkDerivOrigin :: Bool -> CtOrigin #

``mkDerivOrigin` wc` returns `StandAloneDerivOrigin` if `wc` is `True`, and `DerivClauseOrigin` if `wc` is `False`. Useful for error-reporting.

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 #

checkOriginativeSideConditions :: DynFlags -> DerivContext -> Class -> [TcType] -> TyCon -> TyCon -> OriginativeDerivStatus #

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 #