1For the latest version of this document, please see [https://github.com/bos/aeson/blob/master/changelog.md](https://github.com/bos/aeson/blob/master/changelog.md).
5* Catch 0 denominators when parsing Ratio
9* Fix bug in generically derived `FromJSON` instances that are using `unwrapUnaryRecords`, thanks to Xia Li-yao
10* Allow base-compat 0.10.*, thanks to Oleg Grenrus
15* `GKeyValue` has been renamed to `KeyValuePair`, thanks to Xia Li-yao
16* Removed unused `FromJSON` constraint in `withEmbeddedJson`, thanks to Tristan Seligmann
19* Optimizations of TH toEncoding, thanks to Xia Li-yao
20* Optimizations of hex decoding when using the default/pure unescape implementation, thanks to Xia Li-yao
21* Improved error message on `Day` parse failures, thanks to Gershom Bazerman
22* Add `encodeFile` as well as `decodeFile*` variants, thanks to Markus Hauck
23* Documentation fixes, thanks to Lennart Spitzner
24* CPP cleanup, thanks to Ryan Scott
28* Add `Ord` instance for `JSONPathElement`, thanks to Simon Hengel.
33* Added `withEmbeddedJSON` to help parse JSON embedded inside a JSON string, thanks to Jesse Kempf.
34* Memory usage improvements to the default (pure) parser, thanks to Jonathan Paugh. Also thanks to Neil Mitchell & Oleg Grenrus for contributing a benchmark.
35* `omitNothingFields` now works for the `Option` newtype, thanks to Xia Li-yao.
36* Some documentation fixes, thanks to Jonathan Paug & Philippe Crama.
40* Add `FromJSON` and `ToJSON` instances for
41 * `DiffTime`, thanks to Víctor López Juan.
42 * `CTime`, thanks to Daniel Díaz.
43* Fix handling of fractions when parsing Natural, thanks to Yuriy Syrovetskiy.
44* Change text in error messages for Integral types to make them follow the common pattern, thanks to Yuriy Syrovetskiy.
45* Add missing `INCOHERENT` pragma for `RecordToPair`, thanks to Xia Li-yao.
46* Everything related to `Options` is now exported from `Data.Aeson`, thanks to Xia Li-yao.
47* Optimizations to not escape text in clear cases, thanks to Oleg Grenrus.
48* Some documentation fixes, thanks to Phil de Joux & Xia Li-yao.
52* Add `parserThrowError` and `parserCatchError` combinators, thanks to Oleg Grenrus.
54* Add `Generic` instance for `Value`, thanks to Xia Li-yao.
56* Fix a mistake in the 1.2.0.0 changelog, the `cffi` flag is disabled by default! Thanks to dbaynard.
60* `tagSingleConstructors`, an option to encode single-constructor types as tagged sums was added to `Options`. It is disabled by default for backward compatibility.
62* 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.
64* The `Options` constructor is no longer exposed to prevent new options from being breaking changes, use `defaultOptions` instead.
66* The contents of `GToJSON` and `GToEncoding` are no longer exposed.
68* Some INLINE pragmas were removed to avoid GHC running out of simplifier ticks.
72* Fix an accidental change in the format of `deriveJSON`. Thanks to Xia Li-yao!
74* Documentation improvements regarding `ToJSON`, `FromJSON`, and `SumEncoding`. Thanks to Xia Li-yao and Lennart Spitzner!
78* 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 to `False`. This should make aeson compile when C isn't available, such as for GHCJS. Thanks to James Parker & Marcin Tolysz!
80* 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!
84* Added instances for `UUID`.
86* The operators for parsing fields now have named aliases:
87 - `.:` => `parseField`
88 - `.:?` => `parseFieldMaybe`
89 - `.:!` => `parseFieldMaybe'`
90 - These functions now also have variants with explicit parser functions: `explicitParseField`, `explicitParseFieldMaybe`, "explicitParseFieldMaybe'`
91Thanks to Oleg Grenrus.
93* `ToJSONKey (Identity a)` and `FromJSONKey (Identity a)` no longer require the unnecessary `FromJSON a` constraint. Thanks to Oleg Grenrus.
95* Added `Data.Aeson.Encoding.pair'` which is a more general version of `Data.Aeson.Encoding.pair`. Thanks to Andrew Martin.
97* `Day`s BCE are properly encoded and `+` is now a valid prefix for `Day`s CE. Thanks to Matt Parsons.
99* Some commonly used ToJSON instances are now specialized in order to improve compile time. Thanks to Bartosz Nitka.
102[JSONTestSuite](https://github.com/nst/JSONTestSuite) cleanups, all
103motivated by tighter RFC 7159 compliance:
105* The parser now rejects numbers for which
106 [the integer portion contains a leading zero](https://github.com/bos/aeson/commit/3fb7c155f2255482b1b9566ec5c1eaf9895d630e).
107* The parser now rejects numbers for which
108 [a decimal point is not followed by at least one digit](https://github.com/bos/aeson/commit/ecfca35a45286dbe2bbaf5f62354be393bc59b66),
109* The parser now rejects documents that contain [whitespace outside the
110 set {space, newline, carriage return, tab}](https://github.com/bos/aeson/commit/8ef622c2ad8d4a109884e17c2792238a2a320e44).
112Over 90% of JSONTestSuite tests currently pass. The remainder can be
113categorised as follows:
115* The string parser is strict with Unicode compliance where the RFC
116 leaves room for implementation-defined behaviour (tests prefixed
117 with "`i_string_`". (This is necessary because the `text` library
118 cannot accommodate invalid Unicode.)
120* The parser does not (and will not) support UTF-16, UTF-32, or byte
122* The parser accepts unescaped control characters, even though the RFC
123 states that control characters must be escaped. (This may change at
124 some point, but doesn't seem important.)
128* Fixes a regression where a bunch of valid characters caused an
129 "Invalid UTF8-Stream" error when decoding. Thanks to Vladimir
130 Shabanov who investigated and fixed this.
134* Fixes a regression where it was no longer possible to derive
135 instances for types such as `data T a = T { f1 :: a, f2 :: Maybe a
138Thanks to Sean Leather for fixing this, and to Ryan Scott for helping out.
142* Decoding performance has been significantly improved (see
143 https://github.com/bos/aeson/pull/452). Thanks to @winterland1989.
145* Add `ToJSON`/`FromJSON` instances for newtypes from
146 `Data.Semigroup`: `Min`, `Max`, `First`, `Last`, `WrappedMonoid`,
147 `Option`. Thanks to Lennart Spitzner.
149* Make the documentation for `.:!` more accurate. Thanks to Ian Jeffries.
155* Introduced new `FromJSONKey` and `ToJSONKey` type classes that are
156 used to encode maps without going through HashMap. This also allows arbitrary
157 serialization of keys where a string-like key will encode into an object and
158 other keys will encode into an array of key-value tuples.
160* Added higher rank classes: `ToJSON1`, `ToJSON2`, `FromJSON1`, and
163* Added `Data.Aeson.Encoding` with functions to safely write `ToJSON`
164 instances using `toEncoding`.
168* 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 can `cabal install aeson -ffast` and with stack you can add a flag section to your stack.yaml:
175* Added list specific members to `ToJSON` and `FromJSON` classes. In
176 the same way `Read` and `Show` handle lists specifically. This
177 removes need for overlapping instances to handle `String`.
179* Added a new `sumEncoding` option `UntaggedValue` which prevents
180 objects from being tagged with the constructor name.
182* JSONPaths are now tracked in instances derived with template-haskell
185* Get rid of redundancy of JSONPath error messages in nested records.
187 `eitherDecode "{\"x\":{\"a\": [1,2,true]}}" :: Either String Y`
189 `Error in $.x.a[2]: failed to parse field" x: failed to parse field a: expected Int, encountered Boolean`
190 and now yields `Error in $.x.a[2]: expected Int, encountered Boolean"`.
192 Some users might prefer to insert `modifyFailure` themselves to
193 customize error messages, which previously prevented the use of
196* Backwards compatibility with `bytestring-0.9` using the
197 `bytestring-builder` compatibility package.
199* Export `decodeWith`, `decodeStrictWith`, `eitherDecodeWith`, and
200 `eitherDecodeStrictWith` from `Data.Aeson.Parser`. This allows
201 decoding using explicit parsers instead of using `FromJSON`
204* Un-orphan internal instances to render them in haddocks.
208* Integral `FromJSON` instances now only accept integral
209 values. E.g. parsing `3.14` to `Int` fails instead of succeeding
212* Over/underflows are now caught for bounded numeric types.
214* Remove the `contents` field encoding with `allNullaryToStringTag = False`,
215 giving us `{ "tag" : "c1" }` instead of `{ "tag" : "c1", contents : [] }`.
216 The contents field is optional when parsing so this is only a breaking
217 change for ToJSON instances.
219* Fix a bug where `genericToEncoding` with `unwrapUnaryRecords = True`
220 would produce an invalid encoding: `"unwrap\":""`.
222* `ToJSON` instances using `genericToEncoding` and `omitNothingFields`
223 no longer produce invalid JSON.
225* Added instances for `DList`, `Compose`, `Product`, `Sum`.
229* Enable `PolyKinds` to generalize `Proxy`, `Tagged`, and `Const` instances.
230* Add `unsafeToEncoding` in `Data.Aeson.Types`, use with care!
234* Fix build with `base >= 4.8` and `unordered-containers < 0.2.6`.
238* Fix build on TH-less GHCs
242* Fix build with `base < 4.8` and `unordered-containers < 0.2.6`.
243* Add missing field in docs for `defaultOptions`.
247* Fixes a bug where the hashes of equal values could differ.
251The only changes are added instances.
254* `ToJSON a => ToJSON (NonEmpty a)`
255* `FromJSON a => FromJSON (NonEmpty a)`
257* `FromJSON (Proxy a)`
258* `ToJSON b => ToJSON (Tagged a b)`
259* `FromJSON b => FromJSON (Tagged a b)`
260* `ToJSON a => ToJSON (Const a b)`
261* `FromJSON a => FromJSON (Const a b)`
263These are now available for older GHCs:
269This release should be close to backwards compatible with aeson 0.9.
271If you are upgrading from aeson 0.10 it might be easier to go back in
272history to the point you were still using 0.9.
276* Revert `.:?` to behave like it did in 0.9. If you want the 0.10
277 behavior use `.:!` instead.
279* Revert JSON format of `Either` to 0.9, `Left` and `Right` are now
280 serialized with an initial uppercase letter. If you want the names
281 in lowercase you can add a newtype with an instance.
283* All `ToJSON` and `FromJSON` instances except for `[a]` are no longer
284 `OVERLAPPABLE`. Mark your instance as `OVERLAPPING` if it overlaps
285 any of the other aeson instances.
287* All `ToJSON` and `FromJSON` instances except for `[Char]` are no
288 longer incoherent, this means you may need to replace your
289 incoherent instances with a newtyped instance.
293* Introduce `.:!` that behaves like `.:?` did in 0.10.
295* Allow `HH:MM` format for `ZonedTime` and `UTCTime`.
296 This is one of the formats allowed by
297 [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601#Times).
299* Added `ToJSON` and `FromJSON` instances for the
300 `Version`, `Ordering`, and `Natural` types.
304* JSONPath identifiers are now escaped if they contain invalid characters.
306* Fixed JSONPath messages for Seq to include indices.
308* Fixed JSONPath messages for Either to include `left`/`right`.
310* Fix missing quotes surrounding time encodings.
312* Fix #293: Type error in TH when using `omitNothingFields = True`.
316* Various updates to support GHC 8.
321## Performance improvements
323* Direct encoding via the new `toEncoding` method is over 2x faster
324 than `toJSON`. (You must write or code-gen a `toEncoding`
325 implementation to unlock this speedup. See below for details.)
327* Improved string decoding gives a 12% speed win in parsing
328 string-heavy JSON payloads (very common).
330* Encoding and decoding of time-related types are 10x faster (!!) as a
331 result of bypassing `Data.Time.Format` and the arbitrary-precision
334* When using `toEncoding`, `[Char]` can be encoded without a conversion to
335 `Text`. This is fast and efficient.
337* Parsing into an `Object` is now 5% faster and more
338 allocation-efficient.
340## SUBTLE API CHANGES, READ CAREFULLY
342With the exception of long-deprecated code, the API changes below
343**should be upwards compatible** from older versions of `aeson`. If you run
344into upgrade problems, please file an issue with details.
346* The `ToJSON` class has a new method, `toEncoding`, that allows
347 direct encoding from a Haskell value to a lazy bytestring without
348 construction of an intermediate `Value`.
350 The performance benefits of direct encoding are significant: more
351 than 2x faster than before, with less than 1/3 the memory usage.
353 To preserve API compatibility across upgrades from older versions of
354 this library, the default implementation of `toEncoding` uses
355 `toJSON`. You will *not* see any performance improvement unless you
356 write an implementation of `toEncoding`, which can be very simple:
359 instance ToJSON Coord where
360 toEncoding = genericToEncoding defaultOptions
363 (Behind the scenes, the `encode` function uses `toEncoding` now, so
364 if you implement `toEncoding` for your types, you should see a
365 speedup immediately.)
367 If you use Template Haskell or GHC Generics to auto-generate your
368 `ToJSON` instances, you'll benefit from fast toEncoding
369 implementations for free!
371* When converting from a `Value` to a target Haskell type, `FromJSON`
372 instances now provide much better error messages, including a
373 complete JSON path from the root of the object to the offending
374 element. This greatly eases debugging.
376* It is now possible to use Template Haskell to generate `FromJSON`
377 and `ToJSON` instances for types in data families.
379* If you use Template Haskell or generics, and used to use the
380 `camelTo` function to rename fields, the new `camelTo2` function is
381 smarter. For example, `camelTo` will rename `CamelAPICase` to
382 `camelapi_case` (ugh!), while `camelTo2` will map it to
383 `camel_api_case` (yay!).
385* New `ToJSON` and `FromJSON` instances for the following time-related
386 types: `Day`, `LocalTime`.
388* `FromJSON` `UTCTime` parser accepts the same values as for `ZonedTime`,
389 but converts any time zone offset into a UTC time.
391* The `Result` type is now an instance of `Foldable` and `Traversable`.
393* The `Data.Aeson.Generic` module has been removed. It was deprecated in
396* GHC 7.2 and older are no longer supported.
398* The instance of `Monad` for the `Result` type lacked an implementation
399 of `fail` (oops). This has been corrected.
401* Semantics of `(.:?)` operator are changed. It's doesn't anymore accept
402 present `Null` value.
404* Added `(Foldable t, ToJSON a) => ToJSON (t a)` overlappable instance.
405 You might see `No instance for (Foldable YourPolymorphicType) arising from a
406 use of ‘.=’` -errors due this change.
410* A stray export of `encodeToBuilder` got away!
414* The `json` and `json'` parsers are now synonyms for `value` and
415 `value'`, in conformance with the looser semantics of RFC 7159.
417* Renamed `encodeToByteStringBuilder` to the more compact
422* The dependency on the `unordered-containers` package was too lax,
423 and has been corrected.
427* Encoding a `Scientific` value with a huge exponent is now handled
428 efficiently. (This would previously allocate a huge
429 arbitrary-precision integer, potentially leading to a denial of
432* Handling of strings that contain backslash escape sequences is
433 greatly improved. For a pathological string containing almost a
434 megabyte of consecutive backslashes, the new implementation is 27x
435 faster and uses 42x less memory.
437* The `ToJSON` instance for `UTCTime` is rendered with higher
438 (picosecond) resolution.
440* The `value` parser now correctly handles leading whitespace.
442* New instances of `ToJSON` and `FromJSON` for `Data.Sequence` and
443 `Data.Functor.Identity`. The `Value` type now has a `Read` instance.
445* `ZonedTime` parser ordering now favours the standard `JSON` format,
446 increasing efficiency in the common case.
448* Encoding to a `Text.Builder` now escapes `'<'` and `'>'` characters,
453* Fix `ToJSON` instance for 15-tuples (see #223).
461* Add `ToJSON` and `FromJSON` instances for tuples of up to 15
466* Major compiler and library compatibility changes: we have dropped
467 support for GHC older than 7.4, `text` older than 1.1, and
468 `bytestring` older than 0.10.4.0. Supporting the older versions had
469 become increasingly difficult, to the point where it was no longer
474* The performance of encoding to and decoding of bytestrings have both
475 improved by up to 2x, while also using less memory.
477* New dependency: the `scientific` package lets us parse floating point
478 numbers more quickly and accurately.
480* `eitherDecode`, `decodeStrictWith`: fixed bugs.
482* Added `FromJSON` and `ToJSON` instances for `Tree` and `Scientific`.
484* Fixed the `ToJSON` instances for `UTCTime` and `ZonedTime`.
488* Much improved documentation.
490* Angle brackets are now escaped in JSON strings, to help avoid XSS
493* Fixed up handling of nullary constructors when using generic
496* Added `ToJSON`/`FromJSON` instances for:
499 * ISO-8601 dates: `UTCTime`, `ZonedTime`, and `TimeZone`
501* Added accessor functions for inspecting `Value`s.
503* Added `eitherDecode` function that returns an error message if
508* This release introduces a slightly obscure, but
509 backwards-incompatible, change.
511 In the generic APIs of versions 0.4 and 0.5, fields whose names
512 began with a `"_"` character would have this character removed. This
513 no longer occurs, as it was both buggy and surprising
514 (https://github.com/bos/aeson/issues/53).
516* Fixed a bug in generic decoding of nullary constructors
517 (https://github.com/bos/aeson/issues/62).
521* When used with the UTF-8 encoding performance improvements
522 introduced in version 0.11.1.12 of the `text` package, this release
523 improves `aeson`'s JSON encoding performance by 33% relative to
526 As part of achieving this improvement, an API change was necessary.
527 The `fromValue` function in the `Data.Aeson.Encode` module now uses
528 the `text` package's `Builder` type instead of the `blaze-builder`
529 package's `Builder` type.
533* The new `decode` function complements the longstanding `encode`
534 function, and makes the API simpler.
536* New examples make it easier to learn to use the package
537 (https://github.com/bos/aeson/tree/master/examples).
541 `aeson`'s support for data-type generic programming makes it
542 possible to use JSON encodings of most data types without writing
543 any boilerplate instances.
545 Thanks to Bas Van Dijk, `aeson` now supports the two major schemes
546 for doing datatype-generic programming:
548 * the modern mechanism, built into GHC itself
549 (http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html)
551 * the older mechanism, based on SYB (aka "scrap your
554 The modern GHC-based generic mechanism is fast and terse: in fact,
555 its performance is generally comparable in performance to
556 hand-written and TH-derived `ToJSON` and `FromJSON` instances. To
557 see how to use GHC generics, refer to `examples/Generic.hs`.
559 The SYB-based generics support lives in `Data.Aeson.Generic` and is
560 provided mainly for users of GHC older than 7.2. SYB is far slower
561 (by about 10x) than the more modern generic mechanism. To see how
562 to use SYB generics, refer to `examples/GenericSYB.hs`.
564* We switched the intermediate representation of JSON objects from
565 `Data.Map` to `Data.HashMap` which has improved type conversion
568* Instances of `ToJSON` and `FromJSON` for tuples are between 45% and 70%
573 This version of aeson makes explicit the decoupling between
574 *identifying* an element of a JSON document and *converting* it to
575 Haskell. See the `Data.Aeson.Parser` documentation for details.
577 The normal `aeson` `decode` function performs identification
578 strictly, but defers conversion until needed. This can result in
579 improved performance (e.g. if the results of some conversions are
580 never needed), but at a cost in increased memory consumption.
582 The new `decode'` function performs identification and conversion
583 immediately. This incurs an up-front cost in CPU cycles, but
584 reduces reduce memory consumption.
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