aeson
Fast JSON parsing and encoding
https://github.com/haskell/aeson
Version on this page: | 2.1.2.1@rev:4 |
LTS Haskell 22.40: | 2.1.2.1@rev:4 |
Stackage Nightly 2024-11-04: | 2.2.3.0@rev:2 |
Latest on Hackage: | 2.2.3.0@rev:2 |
aeson-2.1.2.1@sha256:aaa8be7ead024f05e9d5b290eb7ee5750deec1137b8f08f7ef039b8cb9036351,6355
Module documentation for 2.1.2.1
Welcome to aeson
aeson is a fast Haskell library for working with JSON data.
Join in!
We are happy to receive bug reports, fixes, documentation enhancements, and other improvements.
Please report bugs via the github issue tracker.
Master git repository:
git clone git://github.com/haskell/aeson.git
See what’s changed in recent (and upcoming) releases:
(You can create and contribute changes using either git or Mercurial.)
Authors
This library was originally written by Bryan O’Sullivan.
Changes
For the latest version of this document, please see https://github.com/haskell/aeson/blob/master/changelog.md.
2.1.2.1
- Support
th-abstraction-0.5
2.1.2.0
- Add
throwDecode :: (MonadThrow m, FromJSON a) => ByteString -> m a
and variants. - Add
Data.Aeson.Decoding
which uses new underlying tokenizer / parser. This parser seems to be faster, and the intermediateTokens
streams allow to differentiate more thanValue
if needed. If no critical issues is found, this parser will become the default in next majoraeson
version. - Support deriving for empty datatypes (such as
Void
andV1
) inFromJSON
andToJSON
. - Add
To/FromJSONKey Void
instances - Fix
FromJSONKey Double
handling of infinities
2.1.1.0
- Add
Data.Aeson.KeyMap.!?
(flipped) alias toData.Aeson.KeyMap.lookup
. - Add
Data.Aeson.KeyMap.insertWith
function. - Use
unsafeDupablePerformIO
instead of incorrectaccursedUnutterablePerformIO
in creation of keys in TH serialisation. This fixes a bug in TH deriving, e.g. whenStrict
pragma was enabled.
2.1.0.0
- Change time instances of types with year (
Day
,UTCTime
) to require years with at least 4 digits. - Change
KeyValue
instances to be more general (and use equality to constraint them) instead of being more lax flexible instances. - Export
Key
type also fromData.Aeson.KeyMap
module. - Export
mapWithKey
fromData.Aeson.KeyMap
module. - Export
ifromJSON
andiparse
fromData.Aeson.Types
. AddiparseEither
. - Add
MonadFix Parser
instance. - Make
Semigroup Series
slightly lazier - Add instances for
Generically
type
2.0.3.0
text-2.0
supportbytestring-0.11.2.0
support- Rewrite pure text literal unescaper.
- Add
QuickCheck
’sArbitrary
,CoArbitrary
andFunction
instances
2.0.2.0
- Add
IsList (KeyMap v)
instance. - Add
toMapText
andfromMapText
toData.Aeson.KeyMap
. - Add
ShortText
instances - Add
Solo
instances
2.0.1.0
- Add
FromJSON KeyMap
instance. - Make
ordered-keymap
on by default.
2.0.0.0
-
Remove forced
-O2
and then unneededfast
flag. Also remove most ofINLINE
pragmas. In the effect,aeson
compiles almost twice as fast.To get
fast
compilation effect cabal-install users may specifyoptimization: False
. -
Make map type used by Object abstract so the underlying implementation can be modified, thanks to Callan McGill
-
Add
ordered-keymap
flag allowing to change the underlying implementation of objectKeyMap
. -
Drop GHC-7 support
-
Remove Data.Aeson.Encode module
-
Double
andFloat
infinities are encoded as"+inf"
and"-inf"
. ChangeTo/FromJSONKey
instances to use"+inf"
and"-inf"
too. -
FromJSON ()
andFromJSON (Proxy tag)
accept any JSON value.
1.5.6.0
- Make
Show Value
instance print object keys in lexicographic order.
1.5.5.1
- Fix a bug in
FromJSON QuarterOfYear
instance.
1.5.5.0
-
Add instances for
Month
,Quarter
andQuarterOfYear
(fromtime-1.11
), thanks to Oleg Grenrus. -
The aeson repository has been moved to the haskell github organization!
1.5.4.1
- Use
Text.Encoding.decodeLatin1
to speed up ASCII string decoding, thanks to Dmitry Ivanov. - Support
bytestring 0.11.*
andth-abstraction 0.4.*
, thanks to Oleg Grenrus.
1.5.4.0
- Add instances for
ToJSONKey
andFromJSONKey
toConst
, thanks to Dan Fithian. - Add support for template-haskell 2.17, thanks to Galen Huntington.
- Documentation typo fix, thanks to Jean-Baptiste Mazon.
1.5.3.0
- Add instances for types in
strict
anddata-fix
packages, thanks to Oleg Grenrus. - CPP cleanup, thanks to Oleg Grenrus.
- Instances for
dlist
’sData.DList.DNonEmpty.DNonEmpty
, thanks to Oleg Grenrus.
1.5.2.0
- Add
Ord Value
instance, thanks to Oleg Grenrus. - Export
rejectUnknownFields
fromData.Aeson
1.5.1.0
- Add instances for
these
, thanks to Oleg Grenrus.
1.5.0.0
- Fix bug in
rejectUnknownFields
not respectingfieldLabelModifier
, thanks to Markus Schirp. GFromJSON
members are no longer exported fromData.Aeson(.Types)
, if you are usinggParseJSON
consider switching togParseJSON'
, thanks to Oleg Grenrus.- Aeson no longer accepts unescaped control characters, thanks to Oleg Grenrus.
- Remove
CoerceText
since GHC >=7.8 hasCoercible
, thanks to Oleg Grenrus. - Rename the
GToJSON
class toGToJSON'
and expose it, thanks to Oleg Grenrus.
Closed tickets: https://github.com/bos/aeson/milestone/21
1.4.7.1
- GHC 8.10 compatibility, thanks to Ryan Scott.
1.4.7.0
Long overdue release (once again), so there’s quite a bit of stuff included even though it’s a “minor” release. Big thanks to all the contributors, the project would not exist without you!
Special thanks to Oleg Grenrus and Xia Li-Yao for reviewing tons of stuff.
New stuff:
- Add
rejectUnknownFields
to Options which rejects unknown fields on deserialization. Useful to find errors during development, but enabling this should be considered a breaking change as previously accepted inputs may now be rejected. Thanks to rmanne.
instance FromJSON Foo where
parseJSON = gParseJSON defaultOptions { rejectUnknownFields = True }
-
FromJSON
instance ofRatio a
now parses numbers in addtion to standard{numerator=..., denumerator=...}
encoding. Thanks to Aleksey Khudyakov. -
Add more information to parse errors, including a sample of the surrounding text. Hopefully this will lead to less “Failed to read: satisfy” confusion! Thanks to Sasha Bogicevic. We expect some downstream test suites to break because of this, apologies in advance. Hopefully you will like the improvement anyway :-)
-
Add
parseFail
toData.Aeson.Types
.parseFail = fail
but doesn’t require users to know aboutMonadFail
. Thanks to Colin Woodbury. -
Make Template Haskell type family detection smarter when deriving
ToJSON1
instances, thanks to Ryan Scott. -
Optimize string parsing for the common case of strings without escapes, thanks to Yuras.
Misc:
-
Clean up compiler warnings and switch from base-compat to base-compat-batteries. Thanks to Colin Woodbury & Oleg Grenrus.
-
Clarification & fixes to documentation regarding treatment of Maybe fields, thanks to Roman Cheplyaka.
-
Add documentation for internal development workflows. Thanks to Guru Devanla.
-
Drop support for GHC < 7.8. We’ve chosen to support older GHCs as long as it doesn’t prevent us from adding new features, but now it does! Thanks to Oleg Grenrus for the patch.
-
Allow generic-deriving 1.13 in test suite.
-
Some DRY fixes thanks to Mark Fajkus.
1.4.6.0
-
Provide a clearer error message when a required tagKey for a constructor is missing, thanks to Guru Devanla. The error message now looks like this:
Error in $: parsing Types.SomeType failed, expected Object with key "tag" containing one of ["nullary","unary","product","record","list"], key "tag" not found
-
Add
formatPath
andformatRelativePath
functions to turn aJSONPath
into aString
, thanks to Robbie McMichael
1.4.5.0
-
Expose
(<?>)
,JSONPath
andJSONPathElement(..)
fromData.Aeson.Types
. Previously only available through internal modules. Thanks to Luke Clifton. -
Support for base-compat 0.11, thanks to Ryan Scott.
-
Travis build for GHC 8.8, thanks to Oleg Grenrus.
1.4.4.0
New features:
-
Adds a parameterized parser
jsonWith
that can be used to choose how to handle duplicate keys in objects, thanks to Xia Li-Yao. -
Add generic implementations of
FromJSONKey
andToJSONKey
, thanks to Xia Li-Yao. Example:
data Foo = Bar
deriving Generic
opts :: JSONKeyOptions
opts = defaultJSONKeyOptions { keyModifier = toLower }
instance ToJSONKey Foo where
toJSONKey = genericToJSONKey opts
instance FromJSONKey Foo where
fromJSONKey = genericFromJSONKey opts
Minor:
- aeson now uses
time-compat
instead oftime-locale-compat
, thanks to Oleg Grenrus. - Prepare for
MonadFail
breakages in GHC 8.8, thanks to Oleg Grenrus. - Require
bytestring >= 0.10.8.1
for newer GHCs to avoid build failures, thanks to Oleg Grenrus. - Support
primitive 0.7.*
, thanks to Adam Bergmark. - Allow
semigroups 0.19.*
andhashable 1.3.*
, thanks to Oleg Grenrus. - Fix a typo in the error message when parsing
NonEmpty
, thanks to Colin Woodbury. - Document surprising behavior when using
omitNothingFields
with type variables, thanks to Xia Li-Yao.
Internal changes:
- Code cleanup by Oleg Grenrus
- Fix dependencies of the benchmarks on older GHC’s, thanks to Xia Li-Yao.
1.4.3.0
- Improve error messages for FromJSON in existing instances and GHC Generic implementation. Thanks to Xia Li-Yao & Igor Pashev.
- Tweak error-reporting combinators and their documentation. Thanks to Xia Li-Yao.
typeMismatch
is now about comparing JSON types (i.e., the expected and actual names of the Value constructor).withObject
and otherwith*
combinators now also mention the JSON types they expect- New
unexpected
andprependFailure
combinators.
- Add
Contravariant
ToJSONKeyFunction
instance. Thanks to Oleg Grenrus. - Add
KeyValue
instance forObject
. Thanks to Robert Hensing. - Improve performance when parsing certain large numbers, thanks to Oleg Grenrus.
- Add
Data.Aeson.QQ.Simple
- A limited version of aeson-qq. Thanks to Oleg Grenrus. - Exposes internal helper functions like
<?>
,JSONPath
, andparseIndexedJSON
fromData.Aeson
module. Thanks to Abid Uzair. - Better error messages when there are syntax errors parsing objects and arrays. Thanks to Fintan Halpenny.
- Support building with
th-abstraction-0.3.0.0
or later. Thanks to Ryan Scott.
1.4.2.0
- Add
Data.Aeson.QQ.Simple
which is a simpler version of theaeson-qq
package, it does not support interpolation, thanks to Oleg Grenrus. - Add
Contravariant ToJSONKeyFunction
instance, thanks to Oleg Grenrus. - Add
KeyValue Object
instance, thanks to Robert Hensing - Improved performance when parsing large numbers, thanks to Oleg Grenrus.
1.4.1.0
- Optimizations of generics, thanks to Rémy Oudompheng, here are some numbers for GHC 8.4:
- Compilation time: G/BigProduct.hs is 25% faster, G/BigRecord.hs is 2x faster.
- Runtime performance: BigRecord/toJSON/generic and BigProduct/encode/generic are more than 2x faster.
- Added To/FromJSON instances for
Void
and Generics’sV1
, thanks to Will Yager - Added To/FromJSON instances for
primitive
’sArray
,SmallArray
,PrimArray
andUnliftedArray
, thanks to Andrew Thad. - Fixes handling of
UTCTime
wrt. leap seconds , thanks to Adam Schønemann - Warning and documentation fixes thanks to tom-bop, Gabor Greif, Ian Jeffries, and Mateusz Curyło.
1.4.0.0
This release introduces bounds on the size of Scientific
numbers when they are converted to other arbitrary precision types that do not represent them efficiently in memory.
This means that trying to decode a number such as 1e1000000000
into an Integer
will now fail instead of using a lot of memory. If you need to represent large numbers you can add a newtype (preferably over Scientific
) and providing a parser using withScientific
.
The following instances are affected by this:
FromJSON Natural
FromJSONKey Natural
FromJSON Integer
FromJSONKey Integer
FromJSON NominalDiffTime
For the same reasons the following instances & functions have been removed:
- Remove
FromJSON Data.Attoparsec.Number
instance. Note thatData.Attoparsec.Number
is deprecated. - Remove deprecated
withNumber
, usewithScientific
instead.
Finally, encoding integral values with large exponents now uses scientific notation, this saves space for large numbers.
1.3.1.1
- Catch 0 denominators when parsing Ratio
1.3.1.0
- Fix bug in generically derived
FromJSON
instances that are usingunwrapUnaryRecords
, thanks to Xia Li-yao - Allow base-compat 0.10.*, thanks to Oleg Grenrus
1.3.0.0
Breaking changes:
GKeyValue
has been renamed toKeyValuePair
, thanks to Xia Li-yao- Removed unused
FromJSON
constraint inwithEmbeddedJson
, thanks to Tristan Seligmann
Other improvements:
- Optimizations of TH toEncoding, thanks to Xia Li-yao
- Optimizations of hex decoding when using the default/pure unescape implementation, thanks to Xia Li-yao
- Improved error message on
Day
parse failures, thanks to Gershom Bazerman - Add
encodeFile
as well asdecodeFile*
variants, thanks to Markus Hauck - Documentation fixes, thanks to Lennart Spitzner
- CPP cleanup, thanks to Ryan Scott
1.2.4.0
- Add
Ord
instance forJSONPathElement
, thanks to Simon Hengel.
1.2.3.0
- Added
withEmbeddedJSON
to help parse JSON embedded inside a JSON string, thanks to Jesse Kempf. - Memory usage improvements to the default (pure) parser, thanks to Jonathan Paugh. Also thanks to Neil Mitchell & Oleg Grenrus for contributing a benchmark.
omitNothingFields
now works for theOption
newtype, thanks to Xia Li-yao.- Some documentation fixes, thanks to Jonathan Paug & Philippe Crama.
1.2.2.0
- Add
FromJSON
andToJSON
instances forDiffTime
, thanks to Víctor López Juan.CTime
, thanks to Daniel Díaz.
- Fix handling of fractions when parsing Natural, thanks to Yuriy Syrovetskiy.
- Change text in error messages for Integral types to make them follow the common pattern, thanks to Yuriy Syrovetskiy.
- Add missing
INCOHERENT
pragma forRecordToPair
, thanks to Xia Li-yao. - Everything related to
Options
is now exported fromData.Aeson
, thanks to Xia Li-yao. - Optimizations to not escape text in clear cases, thanks to Oleg Grenrus.
- Some documentation fixes, thanks to Phil de Joux & Xia Li-yao.
1.2.1.0
-
Add
parserThrowError
andparserCatchError
combinators, thanks to Oleg Grenrus. -
Add
Generic
instance forValue
, thanks to Xia Li-yao. -
Fix a mistake in the 1.2.0.0 changelog, the
cffi
flag is disabled by default! Thanks to dbaynard.
1.2.0.0
-
tagSingleConstructors
, an option to encode single-constructor types as tagged sums was added toOptions
. It is disabled by default for backward compatibility. -
The
cffi
flag is now turned off (False
) by default, this means C FFI code is no longer used by default. You can flip the flag to get C implementation. -
The
Options
constructor is no longer exposed to prevent new options from being breaking changes, usedefaultOptions
instead. -
The contents of
GToJSON
andGToEncoding
are no longer exposed. -
Some INLINE pragmas were removed to avoid GHC running out of simplifier ticks.
1.1.2.0
-
Fix an accidental change in the format of
deriveJSON
. Thanks to Xia Li-yao! -
Documentation improvements regarding
ToJSON
,FromJSON
, andSumEncoding
. Thanks to Xia Li-yao and Lennart Spitzner!
1.1.1.0
-
Added a pure implementation of the C FFI code, the C FFI code. If you wish to use the pure haskell version set the
cffi
flag toFalse
. This should make aeson compile when C isn’t available, such as for GHCJS. Thanks to James Parker & Marcin Tolysz! -
Using the
fast
flag can no longer cause a test case to fail. As far as we know this didn’t affect any users of the library itself. Thanks to Xia Li-yao!
1.1.0.0
-
Added instances for
UUID
. -
The operators for parsing fields now have named aliases:
.:
=>parseField
.:?
=>parseFieldMaybe
.:!
=>parseFieldMaybe'
- These functions now also have variants with explicit parser functions:
explicitParseField
,explicitParseFieldMaybe
, “explicitParseFieldMaybe’` Thanks to Oleg Grenrus.
-
ToJSONKey (Identity a)
andFromJSONKey (Identity a)
no longer require the unnecessaryFromJSON a
constraint. Thanks to Oleg Grenrus. -
Added
Data.Aeson.Encoding.pair'
which is a more general version ofData.Aeson.Encoding.pair
. Thanks to Andrew Martin. -
Day
s BCE are properly encoded and+
is now a valid prefix forDay
s CE. Thanks to Matt Parsons. -
Some commonly used ToJSON instances are now specialized in order to improve compile time. Thanks to Bartosz Nitka.
JSONTestSuite cleanups, all motivated by tighter RFC 7159 compliance:
- The parser now rejects numbers for which the integer portion contains a leading zero.
- The parser now rejects numbers for which a decimal point is not followed by at least one digit,
- The parser now rejects documents that contain whitespace outside the set {space, newline, carriage return, tab}.
Over 90% of JSONTestSuite tests currently pass. The remainder can be categorised as follows:
-
The string parser is strict with Unicode compliance where the RFC leaves room for implementation-defined behaviour (tests prefixed with “
i_string_
”. (This is necessary because thetext
library cannot accommodate invalid Unicode.) -
The parser does not (and will not) support UTF-16, UTF-32, or byte order marks (BOM).
-
The parser accepts unescaped control characters, even though the RFC states that control characters must be escaped. (This may change at some point, but doesn’t seem important.)
1.0.2.1
- Fixes a regression where a bunch of valid characters caused an “Invalid UTF8-Stream” error when decoding. Thanks to Vladimir Shabanov who investigated and fixed this.
1.0.2.0
- Fixes a regression where it was no longer possible to derive
instances for types such as
data T a = T { f1 :: a, f2 :: Maybe a }
.
Thanks to Sean Leather for fixing this, and to Ryan Scott for helping out.
1.0.1.0
-
Decoding performance has been significantly improved (see https://github.com/bos/aeson/pull/452). Thanks to @winterland1989.
-
Add
ToJSON
/FromJSON
instances for newtypes fromData.Semigroup
:Min
,Max
,First
,Last
,WrappedMonoid
,Option
. Thanks to Lennart Spitzner. -
Make the documentation for
.:!
more accurate. Thanks to Ian Jeffries.
1.0.0.0
Major enhancements:
-
Introduced new
FromJSONKey
andToJSONKey
type classes that are used to encode maps without going through HashMap. This also allows arbitrary serialization of keys where a string-like key will encode into an object and other keys will encode into an array of key-value tuples. -
Added higher rank classes:
ToJSON1
,ToJSON2
,FromJSON1
, andFromJSON2
. -
Added
Data.Aeson.Encoding
with functions to safely writeToJSON
instances usingtoEncoding
.
Other enhancements:
- A Cabal
fast
flag was added to disable building with optimizations. This drastically speeds up compiling both aeson and libraries using aeson so it is recommended to enable it during development. With cabal-install you cancabal install aeson -ffast
and with stack you can add a flag section to your stack.yaml:
flags:
aeson:
fast: true
-
Added list specific members to
ToJSON
andFromJSON
classes. In the same wayRead
andShow
handle lists specifically. This removes need for overlapping instances to handleString
. -
Added a new
sumEncoding
optionUntaggedValue
which prevents objects from being tagged with the constructor name. -
JSONPaths are now tracked in instances derived with template-haskell and generics.
-
Get rid of redundancy of JSONPath error messages in nested records.
eitherDecode "{\"x\":{\"a\": [1,2,true]}}" :: Either String Y
previously yieldedError in $.x.a[2]: failed to parse field" x: failed to parse field a: expected Int, encountered Boolean
and now yieldsError in $.x.a[2]: expected Int, encountered Boolean"
.Some users might prefer to insert
modifyFailure
themselves to customize error messages, which previously prevented the use of(.:)
. -
Backwards compatibility with
bytestring-0.9
using thebytestring-builder
compatibility package. -
Export
decodeWith
,decodeStrictWith
,eitherDecodeWith
, andeitherDecodeStrictWith
fromData.Aeson.Parser
. This allows decoding using explicit parsers instead of usingFromJSON
instances. -
Un-orphan internal instances to render them in haddocks.
Other changes:
-
Integral
FromJSON
instances now only accept integral values. E.g. parsing3.14
toInt
fails instead of succeeding with the value3
. -
Over/underflows are now caught for bounded numeric types.
-
Remove the
contents
field encoding withallNullaryToStringTag = False
, giving us{ "tag" : "c1" }
instead of{ "tag" : "c1", contents : [] }
. The contents field is optional when parsing so this is only a breaking change for ToJSON instances. -
Fix a bug where
genericToEncoding
withunwrapUnaryRecords = True
would produce an invalid encoding:"unwrap\":""
. -
ToJSON
instances usinggenericToEncoding
andomitNothingFields
no longer produce invalid JSON. -
Added instances for
DList
,Compose
,Product
,Sum
.
0.11.2.0
- Enable
PolyKinds
to generalizeProxy
,Tagged
, andConst
instances. - Add
unsafeToEncoding
inData.Aeson.Types
, use with care!
0.11.1.4
- Fix build with
base >= 4.8
andunordered-containers < 0.2.6
.
0.11.1.3
- Fix build on TH-less GHCs
0.11.1.2
- Fix build with
base < 4.8
andunordered-containers < 0.2.6
. - Add missing field in docs for
defaultOptions
.
0.11.1.1
- Fixes a bug where the hashes of equal values could differ.
0.11.1.0
The only changes are added instances.
These are new:
ToJSON a => ToJSON (NonEmpty a)
FromJSON a => FromJSON (NonEmpty a)
ToJSON (Proxy a)
FromJSON (Proxy a)
ToJSON b => ToJSON (Tagged a b)
FromJSON b => FromJSON (Tagged a b)
ToJSON a => ToJSON (Const a b)
FromJSON a => FromJSON (Const a b)
These are now available for older GHCs:
ToJSON Natural
FromJSON Natural
0.11.0.0
This release should be close to backwards compatible with aeson 0.9.
If you are upgrading from aeson 0.10 it might be easier to go back in history to the point you were still using 0.9.
Breaking changes:
-
Revert
.:?
to behave like it did in 0.9. If you want the 0.10 behavior use.:!
instead. -
Revert JSON format of
Either
to 0.9,Left
andRight
are now serialized with an initial uppercase letter. If you want the names in lowercase you can add a newtype with an instance. -
All
ToJSON
andFromJSON
instances except for[a]
are no longerOVERLAPPABLE
. Mark your instance asOVERLAPPING
if it overlaps any of the other aeson instances. -
All
ToJSON
andFromJSON
instances except for[Char]
are no longer incoherent, this means you may need to replace your incoherent instances with a newtyped instance.
Additions:
-
Introduce
.:!
that behaves like.:?
did in 0.10. -
Allow
HH:MM
format forZonedTime
andUTCTime
. This is one of the formats allowed by ISO 8601. -
Added
ToJSON
andFromJSON
instances for theVersion
,Ordering
, andNatural
types.
Bug fixes:
-
JSONPath identifiers are now escaped if they contain invalid characters.
-
Fixed JSONPath messages for Seq to include indices.
-
Fixed JSONPath messages for Either to include
left
/right
. -
Fix missing quotes surrounding time encodings.
-
Fix #293: Type error in TH when using
omitNothingFields = True
.
Compatibility:
- Various updates to support GHC 8.
0.10.0.0
Performance improvements
-
Direct encoding via the new
toEncoding
method is over 2x faster thantoJSON
. (You must write or code-gen atoEncoding
implementation to unlock this speedup. See below for details.) -
Improved string decoding gives a 12% speed win in parsing string-heavy JSON payloads (very common).
-
Encoding and decoding of time-related types are 10x faster (!!) as a result of bypassing
Data.Time.Format
and the arbitrary-precisionInteger
type. -
When using
toEncoding
,[Char]
can be encoded without a conversion toText
. This is fast and efficient. -
Parsing into an
Object
is now 5% faster and more allocation-efficient.
SUBTLE API CHANGES, READ CAREFULLY
With the exception of long-deprecated code, the API changes below
should be upwards compatible from older versions of aeson
. If you run
into upgrade problems, please file an issue with details.
-
The
ToJSON
class has a new method,toEncoding
, that allows direct encoding from a Haskell value to a lazy bytestring without construction of an intermediateValue
.The performance benefits of direct encoding are significant: more than 2x faster than before, with less than 1/3 the memory usage.
To preserve API compatibility across upgrades from older versions of this library, the default implementation of
toEncoding
usestoJSON
. You will not see any performance improvement unless you write an implementation oftoEncoding
, which can be very simple:instance ToJSON Coord where toEncoding = genericToEncoding defaultOptions
(Behind the scenes, the
encode
function usestoEncoding
now, so if you implementtoEncoding
for your types, you should see a speedup immediately.)If you use Template Haskell or GHC Generics to auto-generate your
ToJSON
instances, you’ll benefit from fast toEncoding implementations for free! -
When converting from a
Value
to a target Haskell type,FromJSON
instances now provide much better error messages, including a complete JSON path from the root of the object to the offending element. This greatly eases debugging. -
It is now possible to use Template Haskell to generate
FromJSON
andToJSON
instances for types in data families. -
If you use Template Haskell or generics, and used to use the
camelTo
function to rename fields, the newcamelTo2
function is smarter. For example,camelTo
will renameCamelAPICase
tocamelapi_case
(ugh!), whilecamelTo2
will map it tocamel_api_case
(yay!). -
New
ToJSON
andFromJSON
instances for the following time-related types:Day
,LocalTime
. -
FromJSON
UTCTime
parser accepts the same values as forZonedTime
, but converts any time zone offset into a UTC time. -
The
Result
type is now an instance ofFoldable
andTraversable
. -
The
Data.Aeson.Generic
module has been removed. It was deprecated in late 2013. -
GHC 7.2 and older are no longer supported.
-
The instance of
Monad
for theResult
type lacked an implementation offail
(oops). This has been corrected. -
Semantics of
(.:?)
operator are changed. It’s doesn’t anymore accept presentNull
value. -
Added
(Foldable t, ToJSON a) => ToJSON (t a)
overlappable instance. You might seeNo instance for (Foldable YourPolymorphicType) arising from a use of ‘.=’
-errors due this change.
0.9.0.1
- A stray export of
encodeToBuilder
got away!
0.9.0.0
-
The
json
andjson'
parsers are now synonyms forvalue
andvalue'
, in conformance with the looser semantics of RFC 7159. -
Renamed
encodeToByteStringBuilder
to the more compactencodeToBuilder
.
0.8.1.1
- The dependency on the
unordered-containers
package was too lax, and has been corrected.
0.8.1.0
-
Encoding a
Scientific
value with a huge exponent is now handled efficiently. (This would previously allocate a huge arbitrary-precision integer, potentially leading to a denial of service.) -
Handling of strings that contain backslash escape sequences is greatly improved. For a pathological string containing almost a megabyte of consecutive backslashes, the new implementation is 27x faster and uses 42x less memory.
-
The
ToJSON
instance forUTCTime
is rendered with higher (picosecond) resolution. -
The
value
parser now correctly handles leading whitespace. -
New instances of
ToJSON
andFromJSON
forData.Sequence
andData.Functor.Identity
. TheValue
type now has aRead
instance. -
ZonedTime
parser ordering now favours the standardJSON
format, increasing efficiency in the common case. -
Encoding to a
Text.Builder
now escapes'<'
and'>'
characters, to reduce XSS risk.
0.8.0.2
- Fix
ToJSON
instance for 15-tuples (see #223).
0.8.0.1
- Support
time-1.5
.
0.8.0.0
- Add
ToJSON
andFromJSON
instances for tuples of up to 15 elements.
0.7.1.0
- Major compiler and library compatibility changes: we have dropped
support for GHC older than 7.4,
text
older than 1.1, andbytestring
older than 0.10.4.0. Supporting the older versions had become increasingly difficult, to the point where it was no longer worth it.
0.7.0.0
-
The performance of encoding to and decoding of bytestrings have both improved by up to 2x, while also using less memory.
-
New dependency: the
scientific
package lets us parse floating point numbers more quickly and accurately. -
eitherDecode
,decodeStrictWith
: fixed bugs. -
Added
FromJSON
andToJSON
instances forTree
andScientific
. -
Fixed the
ToJSON
instances forUTCTime
andZonedTime
.
0.6 series
-
Much improved documentation.
-
Angle brackets are now escaped in JSON strings, to help avoid XSS attacks.
-
Fixed up handling of nullary constructors when using generic encoding.
-
Added
ToJSON
/FromJSON
instances for:- The
Fixed
class - ISO-8601 dates:
UTCTime
,ZonedTime
, andTimeZone
- The
-
Added accessor functions for inspecting
Value
s. -
Added
eitherDecode
function that returns an error message if decoding fails.
0.5 to 0.6
-
This release introduces a slightly obscure, but backwards-incompatible, change.
In the generic APIs of versions 0.4 and 0.5, fields whose names began with a
"_"
character would have this character removed. This no longer occurs, as it was both buggy and surprising (https://github.com/bos/aeson/issues/53). -
Fixed a bug in generic decoding of nullary constructors (https://github.com/bos/aeson/issues/62).
0.4 to 0.5
-
When used with the UTF-8 encoding performance improvements introduced in version 0.11.1.12 of the
text
package, this release improvesaeson
’s JSON encoding performance by 33% relative toaeson
0.4.As part of achieving this improvement, an API change was necessary. The
fromValue
function in theData.Aeson.Encode
module now uses thetext
package’sBuilder
type instead of theblaze-builder
package’sBuilder
type.
0.3 to 0.4
-
The new
decode
function complements the longstandingencode
function, and makes the API simpler. -
New examples make it easier to learn to use the package (https://github.com/bos/aeson/tree/master/examples).
-
Generics support
aeson
’s support for data-type generic programming makes it possible to use JSON encodings of most data types without writing any boilerplate instances.Thanks to Bas Van Dijk,
aeson
now supports the two major schemes for doing datatype-generic programming:-
the modern mechanism, built into GHC itself (http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html)
-
the older mechanism, based on SYB (aka “scrap your boilerplate”)
The modern GHC-based generic mechanism is fast and terse: in fact, its performance is generally comparable in performance to hand-written and TH-derived
ToJSON
andFromJSON
instances. To see how to use GHC generics, refer toexamples/Generic.hs
.The SYB-based generics support lives in
Data.Aeson.Generic
and is provided mainly for users of GHC older than 7.2. SYB is far slower (by about 10x) than the more modern generic mechanism. To see how to use SYB generics, refer toexamples/GenericSYB.hs
. -
-
We switched the intermediate representation of JSON objects from
Data.Map
toData.HashMap
which has improved type conversion performance. -
Instances of
ToJSON
andFromJSON
for tuples are between 45% and 70% faster than in 0.3. -
Evaluation control
This version of aeson makes explicit the decoupling between identifying an element of a JSON document and converting it to Haskell. See the
Data.Aeson.Parser
documentation for details.The normal
aeson
decode
function performs identification strictly, but defers conversion until needed. This can result in improved performance (e.g. if the results of some conversions are never needed), but at a cost in increased memory consumption.The new
decode'
function performs identification and conversion immediately. This incurs an up-front cost in CPU cycles, but reduces reduce memory consumption.