When accessing field named l :: Symbol of a record s :: *, then the type of the value in that field is FieldType l s.

Definition of this class is based on: https://phabricator.haskell.org/D1687

Provides alternative to the "native" IsLabel instance for getter. Since mixing getter instance and lens instance for IsLabel on polymorphic records is not possible, one may want to use Getter as an alternative.

Since 0.4.1.0

Extract a getter function from overloaded label.

Example:

newtype Bar a = Bar {_bar :: a}

overloadedRecord ''Bar

>>> get #bar (Bar False)
False

Since 0.4.1.0

If field l :: Symbol of a record s :: * is set to new value which has type b :: *, then the modified record will have type UpdateType l s b.

Represents overloaded record fields that can be modified, i.e. updated.

forall l a b s t.
  ModifyField l s t a b => a = b <==> s = t

In other words, if field is modified and its type has changed, then the type of the record has to change as well, and vice versa. Functional dependencies enforce this rule.

Since 0.4.0.0

Using this type family provides more compact type signatures for multiple record fields.

data V3 a = V3
    { _x :: a
    , _y :: a
    , _z :: a
    }
  deriving Show

overloadedRecord def ''V3

setV3
    :: R '["x" ::: a, "y" ::: a, "z" ::: a] r
    => a -> a -> a -> r -> r
setV3 x y z = set' #x x . set' #y y . set' #z z

>>> setV3 0 0 0 (V3 1 1 1 :: V3 Int)
V3 {_x = 0, _y = 0, _z = 0}

Since 0.4.0.0

This type alias is used for more readable type signatures when using R type family.

Since 0.4.0.0

Pass polymorphic record as a value along with all necessary instances. By pattern matching on Rec data constructor all those instances come in to scope.

Example:

{--}
    -- Required in addition to the basic set of language extensions.

data V3 a = V3
    { _x :: a
    , _y :: a
    , _z :: a
    }
  deriving Show

overloadedRecord def ''V3

zeroV3 :: Rec '["x" ::: a, "y" ::: a, "z" ::: a] r -> r -> r
zeroV3 (Rec r) = set' #x 0 . set' #y 0 $ set' #z 0 r

>>> zeroV3 (V3 1 1 1 :: V3 Int)
V3 {_x = 0, _y = 0, _z = 0}

Since 0.4.1.0

Setting is just a form of a Modifier that allows us to specify what was the original type of the value we are changing.

See also Setter, Setter', Modifier, and Modifier'.

Since 0.4.0.0

Same as set, but allows us to use phantom type to restrict the type of a value before it was changed.

newtype Bar a = Bar {_bar :: a}
  deriving Show

overloadedRecord ''Bar

Now we can use setting to change the value stored in Bar. The type signature in following example is not required, it is what type checker would infer.

setting #bar (Proxy @Int) False :: Bar Int -> Bar Bool

Since 0.4.0.0

Wrapper for a set function, lens naming convention is used for type variables. Its instance for IsLabel forces overloaded label to behave as a setter. We could also define Setter as:

type Setter s t b = forall a. Setting a s t b

Notice that the forall a forbids us from stating what exactly it is, therefore functional dependencies in ModifyField type class have to be able to uniquely identify it. If that is not possible, then we may have to use explicit type signature.

See also Setting, Setter', Modifier, and Modifier'.

Definition changed in 0.4.0.0

Extract set function from Setter. Using Modifier instance for IsLabel forces overloaded label to behave as a setter.

Usage example:

newtype Bar a = Bar {_bar :: a}
  deriving Show

overloadedRecord ''Bar

>>> set #bar (Nothing :: Maybe Int) (Bar (Just False))
Bar {_bar = Nothing}

Wrapper for a modification function, lens naming convention is used for type variables. Its instance for IsLabel forces overloaded label to behave as a modification function.

See also Modifier', Setting, Setter, and Setter'.

Since 0.4.0.0

Modify field value using provided function.

Since 0.4.0.0

Same as ModifyField, but type-changing assignment is prohibited.

Since 0.4.0.0

Same as modifyField, but the field type can not be changed.

Since 0.4.0.0

Same as modifyField, but the field type can not be changed.

Since 0.4.0.0

Same as setFiend, but the field type can not be changed.

Since 0.4.0.0

Simple Setter which forbids changing the field type. It can be also defined in terms of Setting:

type Setter' s a = Setting a s s a

See also Setting, Setter, Modifier, and Modifier'.

Definition changed in 0.4.0.0

Same as set, but the field type can not be changed.

Simple Modifier which forbids changing the field type.

See also Modifier, Modifier', Setting, Setter, and Setter'.

Since 0.4.0.0

Same as modify, but the field type can not be changed.

Since 0.4.0.0

Returns True if type a :: * is a function.

Distinguish between getter and lens.