Safe Haskell | None |
---|---|
Language | Haskell2010 |
Synopsis
- class FromJSONPB a where
- parseJSONPB :: Value -> Parser a
- class ToJSONPB a where
- (.:) :: (FromJSONPB a, FieldDefault a) => Object -> Text -> Parser a
- (.=) :: (ToJSONPB v, KeyValuePB kvp, FieldDefault v, Eq v) => Text -> v -> Options -> kvp
- data Options = Options {}
- defaultOptions :: Options
- eitherDecode :: FromJSONPB a => ByteString -> Either String a
- encode :: ToJSONPB a => Options -> a -> ByteString
- object :: [Options -> [Pair]] -> Options -> Value
- pair :: (KeyValuePB m, ToJSONPB v) => Text -> v -> Options -> m
- pairs :: [Options -> Series] -> Options -> Encoding
- parseField :: FromJSONPB a => Object -> Text -> Parser a
- toAesonEncoding :: ToJSONPB a => a -> Encoding
- toAesonValue :: ToJSONPB a => a -> Value
- data Value
- class ToJSON a where
- toJSON :: a -> Value
- toEncoding :: a -> Encoding
- toJSONList :: [a] -> Value
- toEncodingList :: [a] -> Encoding
- class FromJSON a where
- typeMismatch :: String -> Value -> Parser a
- withObject :: String -> (Object -> Parser a) -> Value -> Parser a
Typeclasses
class FromJSONPB a where Source #
Instances
FromJSONPB Bool Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB Double Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB Float Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB Int32 Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB Int64 Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB Word32 Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB Word64 Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB ByteString Source # | |
Defined in Data.ProtoLens.JSONPB.Class parseJSONPB :: Value -> Parser ByteString Source # | |
FromJSONPB Text Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB Text Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB a => FromJSONPB [a] Source # | |
Defined in Data.ProtoLens.JSONPB.Class parseJSONPB :: Value -> Parser [a] Source # | |
FromJSONPB a => FromJSONPB (Maybe a) Source # | |
Defined in Data.ProtoLens.JSONPB.Class | |
FromJSONPB a => FromJSONPB (Vector a) Source # | |
Defined in Data.ProtoLens.JSONPB.Class |
class ToJSONPB a where Source #
toJSONPB :: a -> Options -> Value Source #
toJSON
variant for JSONPB encoders.
toEncodingPB :: a -> Options -> Encoding Source #
toEncoding
variant for JSONPB encoders. If an implementation is not
provided, uses toJSONPB
(which is less efficient since it indirects
through the Value
IR).
Instances
ToJSONPB Bool Source # | |
ToJSONPB Double Source # | |
ToJSONPB Float Source # | |
ToJSONPB Int32 Source # | |
ToJSONPB Int64 Source # | |
ToJSONPB Word32 Source # | |
ToJSONPB Word64 Source # | |
ToJSONPB ByteString Source # | |
Defined in Data.ProtoLens.JSONPB.Class toJSONPB :: ByteString -> Options -> Value Source # toEncodingPB :: ByteString -> Options -> Encoding Source # | |
ToJSONPB Text Source # | |
ToJSONPB Text Source # | |
ToJSONPB a => ToJSONPB [a] Source # | |
ToJSONPB a => ToJSONPB (Maybe a) Source # | |
ToJSONPB a => ToJSONPB (Vector a) Source # | |
Operators
(.:) :: (FromJSONPB a, FieldDefault a) => Object -> Text -> Parser a Source #
.:
variant for JSONPB; if the given key is missing from the
object, or if it is present but its value is null, we produce the default
protobuf value for the field type
(.=) :: (ToJSONPB v, KeyValuePB kvp, FieldDefault v, Eq v) => Text -> v -> Options -> kvp Source #
Options for controlling codec behavior (e.g., emitting default-valued
defaultOptions :: Options Source #
Default options for JSONPB encoding. By default, all options are False
.
JSONPB codec entry points
eitherDecode :: FromJSONPB a => ByteString -> Either String a Source #
eitherDecode
variant for deserializing a JSONPB value from a
lazy ByteString
.
encode :: ToJSONPB a => Options -> a -> ByteString Source #
encode
variant for serializing a JSONPB value as a lazy
ByteString
.
Helper functions
parseField :: FromJSONPB a => Object -> Text -> Parser a Source #
toAesonEncoding :: ToJSONPB a => a -> Encoding Source #
A direct Encoding
for values which can be JSONPB-encoded
toAesonValue :: ToJSONPB a => a -> Value Source #
Aeson re-exports
A JSON value represented as a Haskell value.
Instances
Eq Value | |
Data Value | |
Defined in Data.Aeson.Types.Internal gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Value -> c Value # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Value # dataTypeOf :: Value -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Value) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Value) # gmapT :: (forall b. Data b => b -> b) -> Value -> Value # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Value -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Value -> r # gmapQ :: (forall d. Data d => d -> u) -> Value -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Value -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Value -> m Value # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Value -> m Value # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Value -> m Value # | |
Read Value | |
Show Value | |
IsString Value | |
Defined in Data.Aeson.Types.Internal fromString :: String -> Value # | |
Generic Value | |
Lift Value | |
Hashable Value | |
Defined in Data.Aeson.Types.Internal | |
ToJSON Value | |
Defined in Data.Aeson.Types.ToJSON | |
KeyValue Object | Constructs a singleton |
KeyValue Pair | |
FromJSON Value | |
NFData Value | |
Defined in Data.Aeson.Types.Internal | |
FromString Encoding | |
Defined in Data.Aeson.Types.ToJSON fromString :: String -> Encoding | |
FromString Value | |
Defined in Data.Aeson.Types.ToJSON fromString :: String -> Value | |
GToJSON Encoding arity (U1 :: Type -> Type) | |
GToJSON Value arity (V1 :: Type -> Type) | |
GToJSON Value arity (U1 :: Type -> Type) | |
ToJSON1 f => GToJSON Encoding One (Rec1 f) | |
ToJSON1 f => GToJSON Value One (Rec1 f) | |
ToJSON a => GToJSON Encoding arity (K1 i a :: Type -> Type) | |
(EncodeProduct arity a, EncodeProduct arity b) => GToJSON Encoding arity (a :*: b) | |
ToJSON a => GToJSON Value arity (K1 i a :: Type -> Type) | |
(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) | |
Defined in Data.Aeson.Types.ToJSON | |
v ~ Value => KeyValuePair v (DList Pair) | |
Defined in Data.Aeson.Types.ToJSON | |
KeyValuePB [Pair] Source # | |
(GToJSON Encoding arity a, ConsToJSON Encoding arity a, Constructor c) => SumToJSON' TwoElemArray Encoding arity (C1 c a) | |
Defined in Data.Aeson.Types.ToJSON | |
(GToJSON Value arity a, ConsToJSON Value arity a, Constructor c) => SumToJSON' TwoElemArray Value arity (C1 c a) | |
Defined in Data.Aeson.Types.ToJSON | |
type Rep Value | |
Defined in Data.Aeson.Types.Internal type Rep Value = D1 (MetaData "Value" "Data.Aeson.Types.Internal" "aeson-1.4.5.0-9XSSP6ZPFFF88DbQdSrF7g" False) ((C1 (MetaCons "Object" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Object)) :+: (C1 (MetaCons "Array" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Array)) :+: C1 (MetaCons "String" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Text)))) :+: (C1 (MetaCons "Number" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Scientific)) :+: (C1 (MetaCons "Bool" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 Bool)) :+: C1 (MetaCons "Null" PrefixI False) (U1 :: Type -> Type)))) |
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 two 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.)
Nothing
Convert a Haskell value to a JSON-friendly intermediate type.
toEncoding :: a -> Encoding #
Encode a Haskell value as JSON.
The default implementation of this method creates an
intermediate Value
using toJSON
. This provides
source-level compatibility for people upgrading from older
versions of this library, but obviously offers no performance
advantage.
To benefit from direct encoding, you must provide an
implementation for this method. The easiest way to do so is by
having your types implement Generic
using the DeriveGeneric
extension, and then have GHC generate a method body as follows.
instanceToJSON
Coord wheretoEncoding
=genericToEncoding
defaultOptions
toJSONList :: [a] -> Value #
toEncodingList :: [a] -> Encoding #
Instances
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:
fail
yields a custom error message: it is the recommended way of reporting a failure;empty
(ormzero
) is uninformative: use it when the error is meant to be caught by some(
;<|>
)typeMismatch
can be used to report a failure when the encountered value is not of the expected JSON type;unexpected
is an appropriate alternative when more than one type may be expected, or to keep the expected type implicit.
prependFailure
(or modifyFailure
) add more information to a parser's
error messages.
An example type and instance using typeMismatch
and prependFailure
:
-- 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 useempty
to fail, buttypeMismatch
-- gives a much more informative error message.parseJSON
invalid =prependFailure
"parsing Coord failed, " (typeMismatch
"Object" invalid)
For this common case of only being concerned with a single
type of JSON value, the functions withObject
, withScientific
, 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
Nothing
Instances
:: String | The name of the JSON type being parsed
( |
-> Value | The actual value encountered. |
-> Parser a |
Fail parsing due to a type mismatch, with a descriptive message.
The following wrappers should generally be prefered:
withObject
, withArray
, withText
, withBool
.
Error message example
typeMismatch "Object" (String "oops") -- Error: "expected Object, but encountered String"
withObject :: String -> (Object -> Parser a) -> Value -> Parser a #
applies withObject
name f valuef
to the Object
when value
is an Object
and fails otherwise.
Error message example
withObject "MyType" f (String "oops") -- Error: "parsing MyType failed, expected Object, but encountered String"