Data.OverloadedRecords.TH.Internal

Derive magic instances for OverloadedRecordFields.

Derive OverloadedRecordFields instances

overloadedRecord

Arguments

:: DeriveOverloadedRecordsParams

Parameters for customization of deriving process. Use def to get default behaviour.

-> Name

Name of the type for which magic instances should be derived.

-> DecsQ

Derive magic OverloadedRecordFields instances for specified type.

overloadedRecords

Arguments

:: DeriveOverloadedRecordsParams

Parameters for customization of deriving process. Use def to get default behaviour.

-> [Name]

Names of the types for which magic instances should be derived.

-> DecsQ

Derive magic OverloadedRecordFields instances for specified types.

overloadedRecordFor

Arguments

:: Name

Name of the type for which magic instances should be derived.

-> (DeriveOverloadedRecordsParams -> DeriveOverloadedRecordsParams)

Function that modifies parameters for customization of deriving process.

-> DecsQ

Derive magic OverloadedRecordFields instances for specified type.

Similar to overloadedRecords, but instead of DeriveOverloadedRecordsParams value it takes function which can modify its default value.

data Coordinates2D a
    { coordinateX :: a
    , coordinateY :: a
    }

overloadedRecordsFor ''Coordinates2D
    $ #fieldDerivation .~ \_ _ _ -> \case
        Nothing -> Nothing
        Just field -> lookup field
           [ ("coordinateX", GetterOnlyField "x" Nothing)
           , ("coordinateY", GetterOnlyField "y" Nothing)
           ]

overloadedRecordsFor

Arguments

:: [Name]

Names of the types for which magic instances should be derived.

-> (DeriveOverloadedRecordsParams -> DeriveOverloadedRecordsParams)

Function that modifies parameters for customization of deriving process.

-> DecsQ

Derive magic OverloadedRecordFields instances for specified types.

Customize Derivation Process

data DeriveOverloadedRecordsParams

Parameters for customization of deriving process. Use def to get default behaviour.

Constructors

DeriveOverloadedRecordsParams

Fields

_strictFields :: Bool

Make setter and getter strict. Currently unused.

_fieldDerivation :: FieldDerivation

See FieldDerivation for description.

Instances

Generic DeriveOverloadedRecordsParams

Default DeriveOverloadedRecordsParams

def = DeriveOverloadedRecordsParams
    { strictFields = False
    , fieldDerivation = defaultFieldDerivation
    }

HasField "fieldDerivation" DeriveOverloadedRecordsParams FieldDerivation

ModifyField "fieldDerivation" DeriveOverloadedRecordsParams DeriveOverloadedRecordsParams FieldDerivation FieldDerivation

type Rep DeriveOverloadedRecordsParams

type FieldType "fieldDerivation" DeriveOverloadedRecordsParams = FieldDerivation

type UpdateType "fieldDerivation" DeriveOverloadedRecordsParams FieldDerivation = DeriveOverloadedRecordsParams

fieldDerivation :: IsLabel "fieldDerivation" a => a

Overloaded label that can be used for accessing function of type FieldDerivation from DeriveOverloadedRecordsParams.

This definition is available only if compiled with GHC <8.

type FieldDerivation

Arguments

 = String

Name of the type, of which this field is part of.

-> String

Name of the constructor, of which this field is part of.

-> Word

Field position as an argument of the constructor it is part of. Indexing starts from zero.

-> Maybe String

Name of the field (record) accessor; Nothing means that there is no record accessor defined for it.

-> Maybe OverloadedField

Describes how overloaded record field should be generated for this specific constructor field. Nothing means that no overloaded record field should be derived. See also OverloadedField for details.

Type signature of a function that can customize the derivation of each individual overloaded record field.

If field has an selector then the function will get its name or Nothing otherwise. Function has to return Nothing in case when generating overloaded record field instances is not desired.

data OverloadedField

Describes what should be the name of overloaded record field, and can also provide custom implementation of getter and setter.

Constructors

GetterOnlyField String (Maybe ExpQ)

Derive only getter instances. If second argument is Just, then it contains custom definition of getter function.

GetterAndSetterField String (Maybe (ExpQ, ExpQ))

Derive only getter instances. If second argument is Just, then it contains custom definitions of getter and setter functions, respectively.

Instances

Generic OverloadedField

HasField "fieldDerivation" DeriveOverloadedRecordsParams FieldDerivation

ModifyField "fieldDerivation" DeriveOverloadedRecordsParams DeriveOverloadedRecordsParams FieldDerivation FieldDerivation

type Rep OverloadedField

type UpdateType "fieldDerivation" DeriveOverloadedRecordsParams FieldDerivation = DeriveOverloadedRecordsParams

defaultFieldDerivation :: FieldDerivation

Function used by default value of DeriveOverloadedRecordsParams.

defaultMakeFieldName

Arguments

:: String

Name of the type, of which this field is part of.

-> String

Name of the constructor, of which this field is part of.

-> Word

Field position as an argument of the constructor it is part of. Indexing starts from zero.

-> Maybe String

Name of the field (record) accessor; Nothing means that there is no record accessor defined for it.

-> Maybe String

Overloaded record field name to be used for this specific constructor field; Nothing means that there shouldn't be a label associated with it.

Suppose we have a weird type definition as this:

data SomeType a b c = SomeConstructor
    { _fieldX :: a
    , someTypeFieldY :: b
    , someConstructorFieldZ :: c
    , anythingElse :: (a, b, c)
    }

Then for each of those fields, defaultMakeFieldName will produce expected OverloadedLabel name:

• _fieldX --> fieldX

• someTypeFieldY --> fieldY

• someConstructorFieldZ --> fieldZ

• anythingElse is ignored

Low-level Deriving Mechanism

field

Arguments

:: String

Overloaded label name.

-> TypeQ

Record type.

-> TypeQ

Field type.

-> TypeQ

Record type after update.

-> TypeQ

Setter will set field to a value of this type.

-> ExpQ

Getter function.

-> ExpQ

Setter function.

-> DecsQ

Derive instances for overloaded record field, both getter and setter.

simpleField

Arguments

:: String

Overloaded label name.

-> TypeQ

Record type.

-> TypeQ

Field type.

-> ExpQ

Getter function.

-> ExpQ

Setter function.

-> DecsQ

Derive instances for overloaded record field, both getter and setter. Same as field, but record type is the same before and after update and so is the field type.

fieldGetter

Arguments

:: String

Overloaded label name.

-> TypeQ

Record type.

-> TypeQ

Field type

-> ExpQ

Getter function.

-> DecsQ

Derive instances for overloaded record field getter.

fieldSetter

Arguments

:: String

Overloaded label name.

-> TypeQ

Record type.

-> TypeQ

Field type.

-> TypeQ

Record type after update.

-> TypeQ

Setter will set field to a value of this type.

-> ExpQ

Setter function.

-> DecsQ

Derive instances for overloaded record field setter.

simpleFieldSetter

Arguments

:: String

Overloaded label name.

-> TypeQ

Record type.

-> TypeQ

Field type.

-> ExpQ

Setter function.

-> DecsQ

Derive instances for overloaded record field setter. Same as fieldSetter, but record type is the same before and after update and so is the field type.

Internal Definitions

data DeriveFieldParams

Parameters for deriveForField function.

Constructors

DeriveFieldParams

Fields

typeName :: Name

Record name, i.e. type constructor name.

typeVariables :: [Name]

Free type variables of a type constructor.

constructorName :: Name

Data constructor name.

numberOfArgs :: Word

Number of arguments that data constructor takes.

currentIndex :: Word

Index of the current argument of a data constructor for which we are deriving overloaded record field instances. Indexing starts from zero. In other words currentIndex is between zero (including) and numberOfArgs (excluding).

accessorName :: Maybe Name

Record field accessor, if available, otherwise Nothing.

strictness :: Strict

Strictness annotation of the current data constructor argument.

fieldType :: Type

Type of the current data constructor argument.

deriveForConstructor

Arguments

:: DeriveOverloadedRecordsParams

Parameters for customization of deriving process. Use def to get default behaviour.

-> Name

-> [TyVarBndr]

-> Con

-> DecsQ

Derive magic instances for all fields of a specific data constructor of a specific type.

deriveForField

Arguments

:: DeriveOverloadedRecordsParams

Parameters for customization of deriving process. Use def to get default behaviour.

-> DeriveFieldParams

All the necessary information for derivation procedure.

-> DecsQ

Derive magic instances for a specific field of a specific type.

Helper Functions

newNames :: Word -> String -> Q [Name]

Construct list of new names usin newName.

strTyLitT :: String -> TypeQ

varEs :: [Name] -> [ExpQ]

varPs :: [Name] -> [PatQ]

wildPs :: Word -> [Pat]

Construct list of wildcard patterns (WildP).