Safe Haskell | None |
---|---|
Language | Haskell2010 |
Internal imports.
- join :: Monad m => m (m a) -> m a
- find :: Foldable t => (a -> Bool) -> t a -> Maybe a
- fromMaybe :: a -> Maybe a -> a
- isJust :: Maybe a -> Bool
- keys :: Map k a -> [k]
- (<$>) :: Functor f => (a -> b) -> f a -> f b
- (<*>) :: Applicative f => forall a b. f (a -> b) -> f a -> f b
- view :: MonadReader s m => Getting a s a -> m a
- to :: (Profunctor p, Contravariant f) => (s -> a) -> Optic' * * p f s a
- contains :: Contains m => Index m -> Lens' m Bool
- (^.) :: s -> Getting a s a -> a
- (^?) :: s -> Getting (First a) s a -> Maybe a
- (.~) :: ASetter s t a b -> b -> s -> t
- (?~) :: ASetter s t a (Maybe b) -> b -> s -> t
- (&) :: a -> (a -> b) -> b
- _1 :: Field1 s t a b => Lens s t a b
- _2 :: Field2 s t a b => Lens s t a b
- _Right :: (Choice p, Applicative f) => p a (f b) -> p (Either c a) (f (Either c b))
- data Text :: *
- data IntSet :: *
- fromList :: [Key] -> IntSet
- member :: Key -> IntSet -> Bool
- class FromJSON a where
- parseJSON :: FromJSON a => Value -> Parser a
- class ToJSON a where
- toJSON :: ToJSON a => a -> Value
- data Value :: * = Object !Object
- object :: [Pair] -> Value
- (.=) :: KeyValue kv => forall v. ToJSON v => Text -> v -> kv
- (.:) :: FromJSON a => Object -> Text -> Parser a
- deriveJSON :: Options -> Name -> Q [Dec]
- defaultOptions :: Options
- fieldLabelModifier :: Options -> String -> String
- constructorTagModifier :: Options -> String -> String
Documentation
join :: Monad m => m (m a) -> m a #
The join
function is the conventional monad join operator. It
is used to remove one level of monadic structure, projecting its
bound argument into the outer level.
fromMaybe :: a -> Maybe a -> a #
The fromMaybe
function takes a default value and and Maybe
value. If the Maybe
is Nothing
, it returns the default values;
otherwise, it returns the value contained in the Maybe
.
Examples
Basic usage:
>>>
fromMaybe "" (Just "Hello, World!")
"Hello, World!"
>>>
fromMaybe "" Nothing
""
Read an integer from a string using readMaybe
. If we fail to
parse an integer, we want to return 0
by default:
>>>
import Text.Read ( readMaybe )
>>>
fromMaybe 0 (readMaybe "5")
5>>>
fromMaybe 0 (readMaybe "")
0
O(n). Return all keys of the map in ascending order. Subject to list fusion.
keys (fromList [(5,"a"), (3,"b")]) == [3,5] keys empty == []
(<$>) :: Functor f => (a -> b) -> f a -> f b infixl 4 #
An infix synonym for fmap
.
The name of this operator is an allusion to $
.
Note the similarities between their types:
($) :: (a -> b) -> a -> b (<$>) :: Functor f => (a -> b) -> f a -> f b
Whereas $
is function application, <$>
is function
application lifted over a Functor
.
Examples
Convert from a
to a Maybe
Int
using Maybe
String
show
:
>>>
show <$> Nothing
Nothing>>>
show <$> Just 3
Just "3"
Convert from an
to an Either
Int
Int
Either
Int
String
using show
:
>>>
show <$> Left 17
Left 17>>>
show <$> Right 17
Right "17"
Double each element of a list:
>>>
(*2) <$> [1,2,3]
[2,4,6]
Apply even
to the second element of a pair:
>>>
even <$> (2,2)
(2,True)
(<*>) :: Applicative f => forall a b. f (a -> b) -> f a -> f b infixl 4 #
Sequential application.
A few functors support an implementation of <*>
that is more
efficient than the default one.
view :: MonadReader s m => Getting a s a -> m a #
View the value pointed to by a Getter
, Iso
or
Lens
or the result of folding over all the results of a
Fold
or Traversal
that points
at a monoidal value.
view
.
to
≡id
>>>
view (to f) a
f a
>>>
view _2 (1,"hello")
"hello"
>>>
view (to succ) 5
6
>>>
view (_2._1) ("hello",("world","!!!"))
"world"
As view
is commonly used to access the target of a Getter
or obtain a monoidal summary of the targets of a Fold
,
It may be useful to think of it as having one of these more restricted signatures:
view
::Getter
s a -> s -> aview
::Monoid
m =>Fold
s m -> s -> mview
::Iso'
s a -> s -> aview
::Lens'
s a -> s -> aview
::Monoid
m =>Traversal'
s m -> s -> m
In a more general setting, such as when working with a Monad
transformer stack you can use:
view
::MonadReader
s m =>Getter
s a -> m aview
:: (MonadReader
s m,Monoid
a) =>Fold
s a -> m aview
::MonadReader
s m =>Iso'
s a -> m aview
::MonadReader
s m =>Lens'
s a -> m aview
:: (MonadReader
s m,Monoid
a) =>Traversal'
s a -> m a
to :: (Profunctor p, Contravariant f) => (s -> a) -> Optic' * * p f s a #
contains :: Contains m => Index m -> Lens' m Bool #
>>>
IntSet.fromList [1,2,3,4] ^. contains 3
True
>>>
IntSet.fromList [1,2,3,4] ^. contains 5
False
>>>
IntSet.fromList [1,2,3,4] & contains 3 .~ False
fromList [1,2,4]
(^.) :: s -> Getting a s a -> a infixl 8 #
View the value pointed to by a Getter
or Lens
or the
result of folding over all the results of a Fold
or
Traversal
that points at a monoidal values.
This is the same operation as view
with the arguments flipped.
The fixity and semantics are such that subsequent field accesses can be
performed with (.
).
>>>
(a,b)^._2
b
>>>
("hello","world")^._2
"world"
>>>
import Data.Complex
>>>
((0, 1 :+ 2), 3)^._1._2.to magnitude
2.23606797749979
(^.
) :: s ->Getter
s a -> a (^.
) ::Monoid
m => s ->Fold
s m -> m (^.
) :: s ->Iso'
s a -> a (^.
) :: s ->Lens'
s a -> a (^.
) ::Monoid
m => s ->Traversal'
s m -> m
(^?) :: s -> Getting (First a) s a -> Maybe a infixl 8 #
Perform a safe head
of a Fold
or Traversal
or retrieve Just
the result
from a Getter
or Lens
.
When using a Traversal
as a partial Lens
, or a Fold
as a partial Getter
this can be a convenient
way to extract the optional value.
Note: if you get stack overflows due to this, you may want to use firstOf
instead, which can deal
more gracefully with heavily left-biased trees.
>>>
Left 4 ^?_Left
Just 4
>>>
Right 4 ^?_Left
Nothing
>>>
"world" ^? ix 3
Just 'l'
>>>
"world" ^? ix 20
Nothing
(^?
) ≡flip
preview
(^?
) :: s ->Getter
s a ->Maybe
a (^?
) :: s ->Fold
s a ->Maybe
a (^?
) :: s ->Lens'
s a ->Maybe
a (^?
) :: s ->Iso'
s a ->Maybe
a (^?
) :: s ->Traversal'
s a ->Maybe
a
(.~) :: ASetter s t a b -> b -> s -> t infixr 4 #
Replace the target of a Lens
or all of the targets of a Setter
or Traversal
with a constant value.
This is an infix version of set
, provided for consistency with (.=
).
f<$
a ≡mapped
.~
f$
a
>>>
(a,b,c,d) & _4 .~ e
(a,b,c,e)
>>>
(42,"world") & _1 .~ "hello"
("hello","world")
>>>
(a,b) & both .~ c
(c,c)
(.~
) ::Setter
s t a b -> b -> s -> t (.~
) ::Iso
s t a b -> b -> s -> t (.~
) ::Lens
s t a b -> b -> s -> t (.~
) ::Traversal
s t a b -> b -> s -> t
(?~) :: ASetter s t a (Maybe b) -> b -> s -> t infixr 4 #
Set the target of a Lens
, Traversal
or Setter
to Just
a value.
l?~
t ≡set
l (Just
t)
>>>
Nothing & id ?~ a
Just a
>>>
Map.empty & at 3 ?~ x
fromList [(3,x)]
(?~
) ::Setter
s t a (Maybe
b) -> b -> s -> t (?~
) ::Iso
s t a (Maybe
b) -> b -> s -> t (?~
) ::Lens
s t a (Maybe
b) -> b -> s -> t (?~
) ::Traversal
s t a (Maybe
b) -> b -> s -> t
_1 :: Field1 s t a b => Lens s t a b #
Access the 1st field of a tuple (and possibly change its type).
>>>
(1,2)^._1
1
>>>
_1 .~ "hello" $ (1,2)
("hello",2)
>>>
(1,2) & _1 .~ "hello"
("hello",2)
>>>
_1 putStrLn ("hello","world")
hello ((),"world")
This can also be used on larger tuples as well:
>>>
(1,2,3,4,5) & _1 +~ 41
(42,2,3,4,5)
_1
::Lens
(a,b) (a',b) a a'_1
::Lens
(a,b,c) (a',b,c) a a'_1
::Lens
(a,b,c,d) (a',b,c,d) a a' ..._1
::Lens
(a,b,c,d,e,f,g,h,i) (a',b,c,d,e,f,g,h,i) a a'
_2 :: Field2 s t a b => Lens s t a b #
Access the 2nd field of a tuple.
>>>
_2 .~ "hello" $ (1,(),3,4)
(1,"hello",3,4)
>>>
(1,2,3,4) & _2 *~ 3
(1,6,3,4)
>>>
_2 print (1,2)
2 (1,())
anyOf
_2
:: (s ->Bool
) -> (a, s) ->Bool
traverse
.
_2
:: (Applicative
f,Traversable
t) => (a -> f b) -> t (s, a) -> f (t (s, b))foldMapOf
(traverse
.
_2
) :: (Traversable
t,Monoid
m) => (s -> m) -> t (b, s) -> m
_Right :: (Choice p, Applicative f) => p a (f b) -> p (Either c a) (f (Either c b)) #
This Prism
provides a Traversal
for tweaking the Right
half of an Either
:
>>>
over _Right (+1) (Left 2)
Left 2
>>>
over _Right (+1) (Right 2)
Right 3
>>>
Right "hello" ^._Right
"hello"
>>>
Left "hello" ^._Right :: [Double]
[]
It also can be turned around to obtain the embedding into the Right
half of an Either
:
>>>
_Right # 5
Right 5
>>>
5^.re _Right
Right 5
A space efficient, packed, unboxed Unicode text type.
ToJSON Text | |
KeyValue Pair | |
ToJSONKey Text | |
FromJSON Text | |
FromJSONKey Text | |
Ixed Text | |
SemiSequence Text | |
IsSequence Text | |
Textual Text | |
MonoFunctor Text | |
MonoFoldable Text | |
MonoTraversable Text | |
MonoPointed Text | |
GrowingAppend Text | |
FromAttrVal Text | |
LazySequence Text Text | |
Utf8 Text ByteString | |
FromPairs Value (DList Pair) | |
ToJSON v => GKeyValue v (DList Pair) | |
type Item Text | |
type Index Text | |
type IxValue Text | |
type Index Text | |
type Element Text | |
A set of integers.
IsList IntSet | |
Eq IntSet | |
Data IntSet | |
Ord IntSet | |
Read IntSet | |
Show IntSet | |
Semigroup IntSet | |
Monoid IntSet | |
ToJSON IntSet | |
FromJSON IntSet | |
NFData IntSet | |
Contains IntSet | |
Ixed IntSet | |
At IntSet | |
Wrapped IntSet | |
MonoFoldable IntSet | |
MonoPointed IntSet | |
GrowingAppend IntSet | |
(~) * t IntSet => Rewrapped IntSet t | Use |
type Item IntSet | |
type Index IntSet | |
type IxValue IntSet | |
type Unwrapped IntSet | |
type Element IntSet | |
A type that can be converted from JSON, with the possibility of failure.
In many cases, you can get the compiler to generate parsing code for you (see below). To begin, let's cover writing an instance by hand.
There are various reasons a conversion could fail. For example, an
Object
could be missing a required key, an Array
could be of
the wrong size, or a value could be of an incompatible type.
The basic ways to signal a failed conversion are as follows:
empty
andmzero
work, but are terse and uninformative;fail
yields a custom error message;typeMismatch
produces an informative message for cases when the value encountered is not of the expected type.
An example type and instance using typeMismatch
:
-- Allow ourselves to writeText
literals. {-# LANGUAGE OverloadedStrings #-} data Coord = Coord { x :: Double, y :: Double } instanceFromJSON
Coord whereparseJSON
(Object
v) = Coord<$>
v.:
"x"<*>
v.:
"y" -- We do not expect a non-Object
value here. -- We could usemzero
to fail, buttypeMismatch
-- gives a much more informative error message.parseJSON
invalid =typeMismatch
"Coord" invalid
For this common case of only being concerned with a single
type of JSON value, the functions withObject
, withNumber
, etc.
are provided. Their use is to be preferred when possible, since
they are more terse. Using withObject
, we can rewrite the above instance
(assuming the same language extension and data type) as:
instanceFromJSON
Coord whereparseJSON
=withObject
"Coord" $ \v -> Coord<$>
v.:
"x"<*>
v.:
"y"
Instead of manually writing your FromJSON
instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
parseJSON
.
To use the second, simply add a deriving
clause to your
datatype and declare a Generic
FromJSON
instance for your datatype without giving
a definition for parseJSON
.
For example, the previous example can be simplified to just:
{-# LANGUAGE DeriveGeneric #-} import GHC.Generics data Coord = Coord { x :: Double, y :: Double } derivingGeneric
instanceFromJSON
Coord
The default implementation will be equivalent to
parseJSON =
; If you need different
options, you can customize the generic decoding by defining:genericParseJSON
defaultOptions
customOptions =defaultOptions
{fieldLabelModifier
=map
toUpper
} instanceFromJSON
Coord whereparseJSON
=genericParseJSON
customOptions
FromJSON Bool | |
FromJSON Char | |
FromJSON Double | |
FromJSON Float | |
FromJSON Int | |
FromJSON Int8 | |
FromJSON Int16 | |
FromJSON Int32 | |
FromJSON Int64 | |
FromJSON Integer | WARNING: Only parse Integers from trusted input since an
attacker could easily fill up the memory of the target system by
specifying a scientific number with a big exponent like
|
FromJSON Natural | |
FromJSON Ordering | |
FromJSON Word | |
FromJSON Word8 | |
FromJSON Word16 | |
FromJSON Word32 | |
FromJSON Word64 | |
FromJSON () | |
FromJSON Scientific | |
FromJSON Number | |
FromJSON Text | |
FromJSON UTCTime | |
FromJSON Value | |
FromJSON DotNetTime | |
FromJSON Text | |
FromJSON Version | |
FromJSON CTime | |
FromJSON IntSet | |
FromJSON ZonedTime | Supported string formats:
The first space may instead be a |
FromJSON LocalTime | |
FromJSON TimeOfDay | |
FromJSON NominalDiffTime | WARNING: Only parse lengths of time from trusted input
since an attacker could easily fill up the memory of the target
system by specifying a scientific number with a big exponent like
|
FromJSON DiffTime | WARNING: Only parse lengths of time from trusted input
since an attacker could easily fill up the memory of the target
system by specifying a scientific number with a big exponent like
|
FromJSON Day | |
FromJSON UUID | |
FromJSON a => FromJSON [a] | |
FromJSON a => FromJSON (Maybe a) | |
(FromJSON a, Integral a) => FromJSON (Ratio a) | |
HasResolution a => FromJSON (Fixed a) | WARNING: Only parse fixed-precision numbers from trusted input
since an attacker could easily fill up the memory of the target
system by specifying a scientific number with a big exponent like
|
FromJSON a => FromJSON (Min a) | |
FromJSON a => FromJSON (Max a) | |
FromJSON a => FromJSON (First a) | |
FromJSON a => FromJSON (Last a) | |
FromJSON a => FromJSON (WrappedMonoid a) | |
FromJSON a => FromJSON (Option a) | |
FromJSON a => FromJSON (NonEmpty a) | |
FromJSON a => FromJSON (Identity a) | |
FromJSON a => FromJSON (Dual a) | |
FromJSON a => FromJSON (First a) | |
FromJSON a => FromJSON (Last a) | |
FromJSON a => FromJSON (IntMap a) | |
FromJSON v => FromJSON (Tree v) | |
FromJSON a => FromJSON (Seq a) | |
(Ord a, FromJSON a) => FromJSON (Set a) | |
FromJSON a => FromJSON (DList a) | |
(Prim a, FromJSON a) => FromJSON (Vector a) | |
(Storable a, FromJSON a) => FromJSON (Vector a) | |
(Vector Vector a, FromJSON a) => FromJSON (Vector a) | |
(Eq a, Hashable a, FromJSON a) => FromJSON (HashSet a) | |
FromJSON a => FromJSON (Vector a) | |
(FromJSON a, FromJSON b) => FromJSON (Either a b) | |
(FromJSON a, FromJSON b) => FromJSON (a, b) | |
(FromJSON v, FromJSONKey k, Eq k, Hashable k) => FromJSON (HashMap k v) | |
(FromJSONKey k, Ord k, FromJSON v) => FromJSON (Map k v) | |
FromJSON (Proxy k a) | |
(FromJSON a, FromJSON b, FromJSON c) => FromJSON (a, b, c) | |
FromJSON a => FromJSON (Const k a b) | |
FromJSON b => FromJSON (Tagged k a b) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d) => FromJSON (a, b, c, d) | |
(FromJSON1 f, FromJSON1 g, FromJSON a) => FromJSON (Product * f g a) | |
(FromJSON1 f, FromJSON1 g, FromJSON a) => FromJSON (Sum * f g a) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e) => FromJSON (a, b, c, d, e) | |
(FromJSON1 f, FromJSON1 g, FromJSON a) => FromJSON (Compose * * f g a) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f) => FromJSON (a, b, c, d, e, f) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g) => FromJSON (a, b, c, d, e, f, g) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h) => FromJSON (a, b, c, d, e, f, g, h) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i) => FromJSON (a, b, c, d, e, f, g, h, i) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j) => FromJSON (a, b, c, d, e, f, g, h, i, j) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k) => FromJSON (a, b, c, d, e, f, g, h, i, j, k) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k, FromJSON l) => FromJSON (a, b, c, d, e, f, g, h, i, j, k, l) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k, FromJSON l, FromJSON m) => FromJSON (a, b, c, d, e, f, g, h, i, j, k, l, m) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k, FromJSON l, FromJSON m, FromJSON n) => FromJSON (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | |
(FromJSON a, FromJSON b, FromJSON c, FromJSON d, FromJSON e, FromJSON f, FromJSON g, FromJSON h, FromJSON i, FromJSON j, FromJSON k, FromJSON l, FromJSON m, FromJSON n, FromJSON o) => FromJSON (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | |
A type that can be converted to JSON.
Instances in general must specify toJSON
and should (but don't need
to) specify toEncoding
.
An example type and instance:
-- Allow ourselves to writeText
literals. {-# LANGUAGE OverloadedStrings #-} data Coord = Coord { x :: Double, y :: Double } instanceToJSON
Coord wheretoJSON
(Coord x y) =object
["x".=
x, "y".=
y]toEncoding
(Coord x y) =pairs
("x".=
x<>
"y".=
y)
Instead of manually writing your ToJSON
instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
toJSON
.
To use the second, simply add a deriving
clause to your
datatype and declare a Generic
ToJSON
instance. If you require nothing other than
defaultOptions
, it is sufficient to write (and this is the only
alternative where the default toJSON
implementation is sufficient):
{-# LANGUAGE DeriveGeneric #-} import GHC.Generics data Coord = Coord { x :: Double, y :: Double } derivingGeneric
instanceToJSON
Coord wheretoEncoding
=genericToEncoding
defaultOptions
If on the other hand you wish to customize the generic decoding, you have to implement both methods:
customOptions =defaultOptions
{fieldLabelModifier
=map
toUpper
} instanceToJSON
Coord wheretoJSON
=genericToJSON
customOptionstoEncoding
=genericToEncoding
customOptions
Previous versions of this library only had the toJSON
method. Adding
toEncoding
had to reasons:
- toEncoding is more efficient for the common case that the output of
toJSON
is directly serialized to aByteString
. Further, expressing either method in terms of the other would be non-optimal. - The choice of defaults allows a smooth transition for existing users:
Existing instances that do not define
toEncoding
still compile and have the correct semantics. This is ensured by making the default implementation oftoEncoding
usetoJSON
. This produces correct results, but since it performs an intermediate conversion to aValue
, it will be less efficient than directly emitting anEncoding
. (this also means that specifying nothing more thaninstance ToJSON Coord
would be sufficient as a generically decoding instance, but there probably exists no good reason to not specifytoEncoding
in new instances.)
A JSON value represented as a Haskell value.
Eq Value | |
Data Value | |
Read Value | |
Show Value | |
IsString Value | |
Generic Value | |
Lift Value | |
FromString Encoding | |
FromString Value | |
Hashable Value | |
ToJSON Value | |
KeyValue Pair | |
FromJSON Value | |
NFData Value | |
FromPairs Encoding Series | |
GKeyValue Encoding Series | |
GToJSON Encoding arity (U1 *) | |
GToJSON Value arity (U1 *) | |
ToJSON1 f => GToJSON Encoding One (Rec1 * f) | |
ToJSON1 f => GToJSON Value One (Rec1 * f) | |
ToJSON a => GToJSON Encoding arity (K1 * i a) | |
(EncodeProduct arity a, EncodeProduct arity b) => GToJSON Encoding arity ((:*:) * a b) | |
ToJSON a => GToJSON Value arity (K1 * i a) | |
(WriteProduct arity a, WriteProduct arity b, ProductSize a, ProductSize b) => GToJSON Value arity ((:*:) * a b) | |
(ToJSON1 f, GToJSON Encoding One g) => GToJSON Encoding One ((:.:) * * f g) | |
(ToJSON1 f, GToJSON Value One g) => GToJSON Value One ((:.:) * * f g) | |
FromPairs Value (DList Pair) | |
ToJSON v => GKeyValue v (DList Pair) | |
(GToJSON Encoding arity a, ConsToJSON Encoding arity a, Constructor Meta c) => SumToJSON' * TwoElemArray Encoding arity (C1 * c a) | |
(GToJSON Value arity a, ConsToJSON Value arity a, Constructor Meta c) => SumToJSON' * TwoElemArray Value arity (C1 * c a) | |
type Rep Value | |
(.:) :: FromJSON a => Object -> Text -> Parser a #
Retrieve the value associated with the given key of an Object
.
The result is empty
if the key is not present or the value cannot
be converted to the desired type.
This accessor is appropriate if the key and value must be present
in an object for it to be valid. If the key and value are
optional, use .:?
instead.
:: Options | Encoding options. |
-> Name | Name of the type for which to generate |
-> Q [Dec] |
Generates both ToJSON
and FromJSON
instance declarations for the given
data type or data family instance constructor.
This is a convienience function which is equivalent to calling both
deriveToJSON
and deriveFromJSON
.
Default encoding Options
:
Options
{fieldLabelModifier
= id ,constructorTagModifier
= id ,allNullaryToStringTag
= True ,omitNothingFields
= False ,sumEncoding
=defaultTaggedObject
,unwrapUnaryRecords
= False ,tagSingleConstructors
= False }
fieldLabelModifier :: Options -> String -> String #
Function applied to field labels. Handy for removing common record prefixes for example.
constructorTagModifier :: Options -> String -> String #
Function applied to constructor tags which could be handy for lower-casing them for example.