Safe Haskell	Safe-Inferred
Language	Haskell2010

GHC.Tc.Deriv.Utils

Description

Error-checking and other utilities for deriving clauses or declarations.

Synopsis

type DerivM = ReaderT DerivEnv TcRn
data DerivEnv = DerivEnv {
- denv_overlap_mode :: Maybe OverlapMode
- denv_tvs :: [TyVar]
- denv_cls :: Class
- denv_inst_tys :: [Type]
- denv_ctxt :: DerivContext
- denv_skol_info :: SkolemInfo
- 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_skol_info :: SkolemInfo
- ds_user_ctxt :: UserTypeCtxt
- ds_overlap :: Maybe OverlapMode
- ds_standalone_wildcard :: Maybe SrcSpan
- ds_mechanism :: DerivSpecMechanism
}
pprDerivSpec :: Outputable theta => DerivSpec theta -> SDoc
setDerivSpecTheta :: theta' -> DerivSpec theta -> DerivSpec theta'
zonkDerivSpec :: DerivSpec ThetaType -> TcM (DerivSpec ThetaType)
data DerivSpecMechanism
- = DerivSpecStock {
  - dsm_stock_dit :: DerivInstTys
  - dsm_stock_gen_fns :: StockGenFns
  }
- | DerivSpecNewtype {
  - dsm_newtype_dit :: DerivInstTys
  - dsm_newtype_rep_ty :: Type
  }
- | DerivSpecAnyClass
- | DerivSpecVia {
  - dsm_via_cls_tys :: [Type]
  - dsm_via_inst_ty :: Type
  - dsm_via_ty :: Type
  }
derivSpecMechanismToStrategy :: DerivSpecMechanism -> DerivStrategy GhcTc
isDerivSpecStock :: DerivSpecMechanism -> Bool
isDerivSpecNewtype :: DerivSpecMechanism -> Bool
isDerivSpecAnyClass :: DerivSpecMechanism -> Bool
isDerivSpecVia :: DerivSpecMechanism -> Bool
zonkDerivSpecMechanism :: ZonkEnv -> DerivSpecMechanism -> TcM DerivSpecMechanism
data DerivContext
- = InferContext (Maybe SrcSpan)
- | SupplyContext ThetaType
data OriginativeDerivStatus
- = CanDeriveStock StockGenFns
- | StockClassError !DeriveInstanceErrReason
- | CanDeriveAnyClass
- | NonDerivableClass
data StockGenFns = StockGenFns {
- stock_gen_binds :: SrcSpan -> DerivInstTys -> TcM (LHsBinds GhcPs, [LSig GhcPs], Bag AuxBindSpec, [Name])
- stock_gen_fam_insts :: SrcSpan -> DerivInstTys -> TcM [FamInst]
}
isStandaloneDeriv :: DerivM Bool
isStandaloneWildcardDeriv :: DerivM Bool
askDerivUserTypeCtxt :: DerivM UserTypeCtxt
mkDerivOrigin :: Bool -> CtOrigin
data PredSpec
- = SimplePredSpec {
  - sps_pred :: TcPredType
  - sps_origin :: CtOrigin
  - sps_type_or_kind :: TypeOrKind
  }
- | SubTypePredSpec {
  - stps_ty_actual :: TcSigmaType
  - stps_ty_expected :: TcSigmaType
  - stps_origin :: CtOrigin
  }
type ThetaSpec = [PredSpec]
mkDirectThetaSpec :: CtOrigin -> TypeOrKind -> ThetaType -> ThetaSpec
substPredSpec :: HasCallStack => Subst -> PredSpec -> PredSpec
captureThetaSpecConstraints :: UserTypeCtxt -> ThetaSpec -> TcM (TcLevel, WantedConstraints)
checkOriginativeSideConditions :: DerivInstTys -> DerivM OriginativeDerivStatus
hasStockDeriving :: Class -> Maybe StockGenFns
std_class_via_coercible :: Class -> Bool
non_coercible_class :: Class -> Bool
newDerivClsInst :: DerivSpec ThetaType -> TcM ClsInst
extendLocalInstEnv :: [ClsInst] -> TcM a -> TcM a

Documentation

type DerivM = ReaderT DerivEnv TcRn Source #

To avoid having to manually plumb everything in DerivEnv throughout various functions in GHC.Tc.Deriv and GHC.Tc.Deriv.Infer, we use DerivM, which is a simple reader around TcRn.

data DerivEnv Source #

Contains all of the information known about a derived instance when determining what its EarlyDerivSpec should be. See Note [DerivEnv and DerivSpecMechanism].

Constructors

DerivEnv

Fields

denv_overlap_mode :: Maybe OverlapMode
Is this an overlapping instance?
denv_tvs :: [TyVar]
Universally quantified type variables in the instance. If the denv_ctxt is InferContext, these will be TcTyVar skolems. If the denv_ctxt is SupplyContext, these will be ordinary TyVars. See Note [Overlap and deriving] in GHC.Tc.Deriv.Infer.
All type variables that appear in the denv_inst_tys, denv_ctxt, denv_skol_info, and denv_strat should come from denv_tvs.
denv_cls :: Class
Class for which we need to derive an instance
denv_inst_tys :: [Type]
All arguments to denv_cls in the derived instance.
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_skol_info :: SkolemInfo
The SkolemInfo used to skolemise the denv_tvs in the case where the denv_ctxt is InferContext.
denv_strat :: Maybe (DerivStrategy GhcTc)
Just if user requests a particular deriving strategy. Otherwise, Nothing.

Instances

Instances details

Outputable DerivEnv Source #
Instance details Defined in GHC.Tc.Deriv.Utils Methods ppr :: DerivEnv -> SDoc Source #

data DerivSpec theta Source #

Constructors

DS
Fields ds_loc :: SrcSpan ds_name :: Name ds_tvs :: [TyVar] ds_theta :: theta ds_cls :: Class ds_tys :: [Type] ds_skol_info :: SkolemInfo ds_user_ctxt :: UserTypeCtxt ds_overlap :: Maybe OverlapMode ds_standalone_wildcard :: Maybe SrcSpan ds_mechanism :: DerivSpecMechanism

Instances

Instances details

Outputable theta => Outputable (DerivSpec theta) Source #
Instance details Defined in GHC.Tc.Deriv.Utils Methods ppr :: DerivSpec theta -> SDoc Source #

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

setDerivSpecTheta :: theta' -> DerivSpec theta -> DerivSpec theta' Source #

Set the ds_theta in a DerivSpec.

zonkDerivSpec :: DerivSpec ThetaType -> TcM (DerivSpec ThetaType) Source #

Zonk the TcTyVars in a DerivSpec to TyVars. See Note [What is zonking?] in GHC.Tc.Utils.TcMType.

This is only used in the final zonking step when inferring the context for a derived instance. See Note [Overlap and deriving] in GHC.Tc.Deriv.Infer.

data DerivSpecMechanism Source #

What action to take in order to derive a class instance. See Note [DerivEnv and DerivSpecMechanism], as well as Note [Deriving strategies] in GHC.Tc.Deriv.

Constructors

DerivSpecStock	"Standard" classes
Fields dsm_stock_dit :: DerivInstTys Information about the arguments to the class in the derived instance, including what type constructor the last argument is headed by. See `Note [DerivEnv and DerivSpecMechanism]`. dsm_stock_gen_fns :: StockGenFns How to generate the instance bindings and associated type family instances.
DerivSpecNewtype	GeneralizedNewtypeDeriving
Fields dsm_newtype_dit :: DerivInstTys Information about the arguments to the class in the derived instance, including what type constructor the last argument is headed by. See `Note [DerivEnv and DerivSpecMechanism]`. dsm_newtype_rep_ty :: Type The newtype rep type.
DerivSpecAnyClass	DeriveAnyClass
DerivSpecVia	DerivingVia
Fields dsm_via_cls_tys :: [Type] All arguments to the class besides the last one. dsm_via_inst_ty :: Type The last argument to the class. dsm_via_ty :: Type The `via` type

Instances

Instances details

Outputable DerivSpecMechanism Source #
Instance details Defined in GHC.Tc.Deriv.Utils Methods ppr :: DerivSpecMechanism -> SDoc Source #

derivSpecMechanismToStrategy :: DerivSpecMechanism -> DerivStrategy GhcTc Source #

Convert a DerivSpecMechanism to its corresponding DerivStrategy.

isDerivSpecStock :: DerivSpecMechanism -> Bool Source #

isDerivSpecNewtype :: DerivSpecMechanism -> Bool Source #

isDerivSpecAnyClass :: DerivSpecMechanism -> Bool Source #

isDerivSpecVia :: DerivSpecMechanism -> Bool Source #

zonkDerivSpecMechanism :: ZonkEnv -> DerivSpecMechanism -> TcM DerivSpecMechanism Source #

Zonk the TcTyVars in a DerivSpecMechanism to TyVars. See Note [What is zonking?] in GHC.Tc.Utils.TcMType.

This is only used in the final zonking step when inferring the context for a derived instance. See Note [Overlap and deriving] in GHC.Tc.Deriv.Infer.

data DerivContext Source #

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

Instances details

Outputable DerivContext Source #
Instance details Defined in GHC.Tc.Deriv.Utils Methods ppr :: DerivContext -> SDoc Source #

data OriginativeDerivStatus Source #

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 GHC.Tc.Deriv.

Constructors

CanDeriveStock StockGenFns
StockClassError !DeriveInstanceErrReason
CanDeriveAnyClass
NonDerivableClass

data StockGenFns Source #

Describes how to generate instance bindings (stock_gen_binds) and associated type family instances (stock_gen_fam_insts) for a particular stock-derived instance.

Constructors

StockGenFns

Fields

stock_gen_binds :: SrcSpan -> DerivInstTys -> TcM (LHsBinds GhcPs, [LSig GhcPs], Bag AuxBindSpec, [Name])
Describes how to generate instance bindings for a stock-derived instance.
This function takes two arguments:
1. SrcSpan: the source location where the instance is being derived. This will eventually be instantiated with the ds_loc field of a DerivSpec.
2. DerivInstTys: information about the argument types to which a class is applied in a derived instance. This will eventually be instantiated with the dsm_stock_dit field of a DerivSpecMechanism.
This function returns four things:
1. LHsBinds GhcPass: The derived instance's function bindings (e.g., compare (T x) (T y) = compare x y)
2. [LSig GhcPass]: A list of instance specific signatures/pragmas. Most likely INLINE pragmas for class methods.
3. Bag AuxBindSpec: Auxiliary bindings needed to support the derived instance. As examples, derived Eq and Ord instances sometimes require top-level con2tag functions. See Note [Auxiliary binders] in GHC.Tc.Deriv.Generate.
4. [Name]: A list of Names for which -Wunused-binds should be suppressed. This is used to suppress unused warnings for record selectors when deriving Read, Show, or Generic. See Note [Deriving and unused record selectors].
stock_gen_fam_insts :: SrcSpan -> DerivInstTys -> TcM [FamInst]
Describes how to generate associated type family instances for a stock-derived instance. This function takes the same arguments as the stock_gen_binds function but returns a list of FamInsts instead. Generating type family instances is done separately from stock_gen_binds since the type family instances must be generated before the instance bindings can be typechecked. See Note [Staging of tcDeriving] in GHC.Tc.Deriv.

isStandaloneDeriv :: DerivM Bool Source #

Is GHC processing a standalone deriving declaration?

isStandaloneWildcardDeriv :: DerivM Bool Source #

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

askDerivUserTypeCtxt :: DerivM UserTypeCtxt Source #

Return InstDeclCtxt if processing with a standalone deriving declaration or DerivClauseCtxt if processing a deriving clause.

mkDerivOrigin :: Bool -> CtOrigin Source #

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

data PredSpec Source #

A PredSpec specifies a constraint to emitted when inferring the instance context for a derived instance in simplifyInfer.

Constructors

SimplePredSpec	An ordinary `PredSpec` that directly stores a `PredType`, which will be emitted as a wanted constraint in the constraint solving machinery. This is the simple case, as there are no skolems, metavariables, or given constraints involved.
Fields sps_pred :: TcPredType The constraint to emit as a wanted sps_origin :: CtOrigin The origin of the constraint sps_type_or_kind :: TypeOrKind Whether the constraint is a type or kind
SubTypePredSpec	A special `PredSpec` that is only used by `DeriveAnyClass`. This will check if `stps_ty_actual` is a subtype of (i.e., more polymorphic than) `stps_ty_expected` in the constraint solving machinery, emitting an implication constraint as a side effect. For more details on how this works, see `Note [Gathering and simplifying constraints for DeriveAnyClass]` in GHC.Tc.Deriv.Infer.
Fields stps_ty_actual :: TcSigmaType The actual type. In the context of `DeriveAnyClass`, this is the default method type signature. stps_ty_expected :: TcSigmaType The expected type. In the context of `DeriveAnyClass`, this is the original method type signature. stps_origin :: CtOrigin The origin of the constraint

Instances

Instances details

Outputable PredSpec Source #
Instance details Defined in GHC.Tc.Deriv.Utils Methods ppr :: PredSpec -> SDoc Source #

type ThetaSpec = [PredSpec] Source #

A list of PredSpec constraints to simplify when inferring a derived instance's context. For the stock, newtype, and via deriving strategies, these will consist of SimplePredSpecs, and for DeriveAnyClass, these will consist of SubTypePredSpecs. Here is an example to illustrate the latter:

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 SubTypePredSpecs, one for each method:

[ SubTypePredSpec
    { stps_ty_actual   = forall y. (Show (Quux q), Ix y) => Quux q -> y -> String
    , stps_ty_expected = forall b.                (Ix b) => Quux q -> b -> String
    , stps_ty_origin   = DerivClauseCtxt
    }
, SubTypePredSpec
    { stps_ty_actual   = Ord (Quux q) => Quux q -> Quux q -> Bool
    , stps_ty_expected = Eq  (Quux q) => Quux q -> Quux q -> Bool
    , stps_ty_origin   = DerivClauseCtxt
    }
]

(Note that the type variable q is bound by the data type Quux, and thus appears free in the stps_ty_actuals and stps_ty_expecteds.)

See Note [Gathering and simplifying constraints for DeriveAnyClass] in GHC.Tc.Deriv.Infer for an explanation of how these SubTypePredSpecs are used to compute implication constraints.

mkDirectThetaSpec :: CtOrigin -> TypeOrKind -> ThetaType -> ThetaSpec Source #

Build a list of SimplePredSpecs, using the supplied CtOrigin and TypeOrKind values for each PredType.

substPredSpec :: HasCallStack => Subst -> PredSpec -> PredSpec Source #

captureThetaSpecConstraints Source #

Arguments

:: UserTypeCtxt	Used to inform error messages as to whether we are in a `deriving` clause or a standalone `deriving` declaration
-> ThetaSpec	The specs from which constraints will be created
-> TcM (TcLevel, WantedConstraints)

Capture wanted constraints from a ThetaSpec.

checkOriginativeSideConditions :: DerivInstTys -> DerivM OriginativeDerivStatus Source #

hasStockDeriving :: Class -> Maybe StockGenFns Source #

std_class_via_coercible :: Class -> Bool Source #

non_coercible_class :: Class -> Bool Source #

newDerivClsInst :: DerivSpec ThetaType -> TcM ClsInst Source #

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