TcDerivUtils

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

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)

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

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

Methods

ppr :: PredOrigin -> SDoc

pprPrec :: Rational -> PredOrigin -> SDoc

data ThetaOrigin

A list of wanted PredOrigin constraints (to_wanted_origins) alongside any corresponding given constraints (to_givens) and locally quantified type variables (to_tvs).

In most cases, to_givens will be empty, as most deriving mechanisms (e.g., stock and newtype deriving) do not require given constraints. The exception is DeriveAnyClass, which can involve given constraints. For example, if you tried to derive an instance for the following class using DeriveAnyClass:

class Foo a where
  bar :: a -> b -> String
  default bar :: (Show a, Ix b) => a -> b -> String
  bar = show

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

Then it would generate two ThetaOrigins, one for each method:

[ ThetaOrigin { to_tvs            = [b]
              , to_givens         = []
              , to_wanted_origins = [Show a, Ix b] }
, ThetaOrigin { to_tvs            = []
              , to_givens         = [Eq a]
              , to_wanted_origins = [Ord a] }
]

Constructors

ThetaOrigin

Fields

• to_tvs :: [TyVar]
• to_givens :: ThetaType
• to_wanted_origins :: [PredOrigin]

Instances

Outputable ThetaOrigin

Methods

ppr :: ThetaOrigin -> SDoc

pprPrec :: Rational -> ThetaOrigin -> SDoc

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

mkThetaOrigin :: CtOrigin -> TypeOrKind -> [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