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).
6* `GKeyValue` has been renamed to `KeyValuePair`, thanks to Xia Li-yao
7* Removed unused `FromJSON` constraint in `withEmbeddedJson`, thanks to Tristan Seligmann
10* Optimizations of TH toEncoding, thanks to Xia Li-yao
11* Optimizations of hex decoding when using the default/pure unescape implementation, thanks to Xia Li-yao
12* Improved error message on `Day` parse failures, thanks to Gershom Bazerman
13* Add `encodeFile` as well as `decodeFile*` variants, thanks to Markus Hauck
14* Documentation fixes, thanks to Lennart Spitzner
15* CPP cleanup, thanks to Ryan Scott
19* Add `Ord` instance for `JSONPathElement`, thanks to Simon Hengel.
24* Added `withEmbeddedJSON` to help parse JSON embedded inside a JSON string, thanks to Jesse Kempf.
25* Memory usage improvements to the default (pure) parser, thanks to Jonathan Paugh. Also thanks to Neil Mitchell & Oleg Grenrus for contributing a benchmark.
26* `omitNothingFields` now works for the `Option` newtype, thanks to Xia Li-yao.
27* Some documentation fixes, thanks to Jonathan Paug & Philippe Crama.
31* Add `FromJSON` and `ToJSON` instances for
32 * `DiffTime`, thanks to Víctor López Juan.
33 * `CTime`, thanks to Daniel Díaz.
34* Fix handling of fractions when parsing Natural, thanks to Yuriy Syrovetskiy.
35* Change text in error messages for Integral types to make them follow the common pattern, thanks to Yuriy Syrovetskiy.
36* Add missing `INCOHERENT` pragma for `RecordToPair`, thanks to Xia Li-yao.
37* Everything related to `Options` is now exported from `Data.Aeson`, thanks to Xia Li-yao.
38* Optimizations to not escape text in clear cases, thanks to Oleg Grenrus.
39* Some documentation fixes, thanks to Phil de Joux & Xia Li-yao.
43* Add `parserThrowError` and `parserCatchError` combinators, thanks to Oleg Grenrus.
45* Add `Generic` instance for `Value`, thanks to Xia Li-yao.
47* Fix a mistake in the 1.2.0.0 changelog, the `cffi` flag is disabled by default! Thanks to dbaynard.
51* `tagSingleConstructors`, an option to encode single-constructor types as tagged sums was added to `Options`. It is disabled by default for backward compatibility.
53* 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.
55* The `Options` constructor is no longer exposed to prevent new options from being breaking changes, use `defaultOptions` instead.
57* The contents of `GToJSON` and `GToEncoding` are no longer exposed.
59* Some INLINE pragmas were removed to avoid GHC running out of simplifier ticks.
63* Fix an accidental change in the format of `deriveJSON`. Thanks to Xia Li-yao!
65* Documentation improvements regarding `ToJSON`, `FromJSON`, and `SumEncoding`. Thanks to Xia Li-yao and Lennart Spitzner!
69* 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!
71* 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!
75* Added instances for `UUID`.
77* The operators for parsing fields now have named aliases:
78 - `.:` => `parseField`
79 - `.:?` => `parseFieldMaybe`
80 - `.:!` => `parseFieldMaybe'`
81 - These functions now also have variants with explicit parser functions: `explicitParseField`, `explicitParseFieldMaybe`, "explicitParseFieldMaybe'`
82Thanks to Oleg Grenrus.
84* `ToJSONKey (Identity a)` and `FromJSONKey (Identity a)` no longer require the unnecessary `FromJSON a` constraint. Thanks to Oleg Grenrus.
86* Added `Data.Aeson.Encoding.pair'` which is a more general version of `Data.Aeson.Encoding.pair`. Thanks to Andrew Martin.
88* `Day`s BCE are properly encoded and `+` is now a valid prefix for `Day`s CE. Thanks to Matt Parsons.
90* Some commonly used ToJSON instances are now specialized in order to improve compile time. Thanks to Bartosz Nitka.
93[JSONTestSuite](https://github.com/nst/JSONTestSuite) cleanups, all
94motivated by tighter RFC 7159 compliance:
96* The parser now rejects numbers for which
97 [the integer portion contains a leading zero](https://github.com/bos/aeson/commit/3fb7c155f2255482b1b9566ec5c1eaf9895d630e).
98* The parser now rejects numbers for which
99 [a decimal point is not followed by at least one digit](https://github.com/bos/aeson/commit/ecfca35a45286dbe2bbaf5f62354be393bc59b66),
100* The parser now rejects documents that contain [whitespace outside the
101 set {space, newline, carriage return, tab}](https://github.com/bos/aeson/commit/8ef622c2ad8d4a109884e17c2792238a2a320e44).
103Over 90% of JSONTestSuite tests currently pass. The remainder can be
104categorised as follows:
106* The string parser is strict with Unicode compliance where the RFC
107 leaves room for implementation-defined behaviour (tests prefixed
108 with "`i_string_`". (This is necessary because the `text` library
109 cannot accommodate invalid Unicode.)
111* The parser does not (and will not) support UTF-16, UTF-32, or byte
113* The parser accepts unescaped control characters, even though the RFC
114 states that control characters must be escaped. (This may change at
115 some point, but doesn't seem important.)
119* Fixes a regression where a bunch of valid characters caused an
120 "Invalid UTF8-Stream" error when decoding. Thanks to Vladimir
121 Shabanov who investigated and fixed this.
125* Fixes a regression where it was no longer possible to derive
126 instances for types such as `data T a = T { f1 :: a, f2 :: Maybe a
129Thanks to Sean Leather for fixing this, and to Ryan Scott for helping out.
133* Decoding performance has been significantly improved (see
134 https://github.com/bos/aeson/pull/452). Thanks to @winterland1989.
136* Add `ToJSON`/`FromJSON` instances for newtypes from
137 `Data.Semigroup`: `Min`, `Max`, `First`, `Last`, `WrappedMonoid`,
138 `Option`. Thanks to Lennart Spitzner.
140* Make the documentation for `.:!` more accurate. Thanks to Ian Jeffries.
146* Introduced new `FromJSONKey` and `ToJSONKey` type classes that are
147 used to encode maps without going through HashMap. This also allows arbitrary
148 serialization of keys where a string-like key will encode into an object and
149 other keys will encode into an array of key-value tuples.
151* Added higher rank classes: `ToJSON1`, `ToJSON2`, `FromJSON1`, and
154* Added `Data.Aeson.Encoding` with functions to safely write `ToJSON`
155 instances using `toEncoding`.
159* 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:
166* Added list specific members to `ToJSON` and `FromJSON` classes. In
167 the same way `Read` and `Show` handle lists specifically. This
168 removes need for overlapping instances to handle `String`.
170* Added a new `sumEncoding` option `UntaggedValue` which prevents
171 objects from being tagged with the constructor name.
173* JSONPaths are now tracked in instances derived with template-haskell
176* Get rid of redundancy of JSONPath error messages in nested records.
178 `eitherDecode "{\"x\":{\"a\": [1,2,true]}}" :: Either String Y`
180 `Error in $.x.a[2]: failed to parse field" x: failed to parse field a: expected Int, encountered Boolean`
181 and now yields `Error in $.x.a[2]: expected Int, encountered Boolean"`.
183 Some users might prefer to insert `modifyFailure` themselves to
184 customize error messages, which previously prevented the use of
187* Backwards compatibility with `bytestring-0.9` using the
188 `bytestring-builder` compatibility package.
190* Export `decodeWith`, `decodeStrictWith`, `eitherDecodeWith`, and
191 `eitherDecodeStrictWith` from `Data.Aeson.Parser`. This allows
192 decoding using explicit parsers instead of using `FromJSON`
195* Un-orphan internal instances to render them in haddocks.
199* Integral `FromJSON` instances now only accept integral
200 values. E.g. parsing `3.14` to `Int` fails instead of succeeding
203* Over/underflows are now caught for bounded numeric types.
205* Remove the `contents` field encoding with `allNullaryToStringTag = False`,
206 giving us `{ "tag" : "c1" }` instead of `{ "tag" : "c1", contents : [] }`.
207 The contents field is optional when parsing so this is only a breaking
208 change for ToJSON instances.
210* Fix a bug where `genericToEncoding` with `unwrapUnaryRecords = True`
211 would produce an invalid encoding: `"unwrap\":""`.
213* `ToJSON` instances using `genericToEncoding` and `omitNothingFields`
214 no longer produce invalid JSON.
216* Added instances for `DList`, `Compose`, `Product`, `Sum`.
220* Enable `PolyKinds` to generalize `Proxy`, `Tagged`, and `Const` instances.
221* Add `unsafeToEncoding` in `Data.Aeson.Types`, use with care!
225* Fix build with `base >= 4.8` and `unordered-containers < 0.2.6`.
229* Fix build on TH-less GHCs
233* Fix build with `base < 4.8` and `unordered-containers < 0.2.6`.
234* Add missing field in docs for `defaultOptions`.
238* Fixes a bug where the hashes of equal values could differ.
242The only changes are added instances.
245* `ToJSON a => ToJSON (NonEmpty a)`
246* `FromJSON a => FromJSON (NonEmpty a)`
248* `FromJSON (Proxy a)`
249* `ToJSON b => ToJSON (Tagged a b)`
250* `FromJSON b => FromJSON (Tagged a b)`
251* `ToJSON a => ToJSON (Const a b)`
252* `FromJSON a => FromJSON (Const a b)`
254These are now available for older GHCs:
260This release should be close to backwards compatible with aeson 0.9.
262If you are upgrading from aeson 0.10 it might be easier to go back in
263history to the point you were still using 0.9.
267* Revert `.:?` to behave like it did in 0.9. If you want the 0.10
268 behavior use `.:!` instead.
270* Revert JSON format of `Either` to 0.9, `Left` and `Right` are now
271 serialized with an initial uppercase letter. If you want the names
272 in lowercase you can add a newtype with an instance.
274* All `ToJSON` and `FromJSON` instances except for `[a]` are no longer
275 `OVERLAPPABLE`. Mark your instance as `OVERLAPPING` if it overlaps
276 any of the other aeson instances.
278* All `ToJSON` and `FromJSON` instances except for `[Char]` are no
279 longer incoherent, this means you may need to replace your
280 incoherent instances with a newtyped instance.
284* Introduce `.:!` that behaves like `.:?` did in 0.10.
286* Allow `HH:MM` format for `ZonedTime` and `UTCTime`.
287 This is one of the formats allowed by
288 [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601#Times).
290* Added `ToJSON` and `FromJSON` instances for the
291 `Version`, `Ordering`, and `Natural` types.
295* JSONPath identifiers are now escaped if they contain invalid characters.
297* Fixed JSONPath messages for Seq to include indices.
299* Fixed JSONPath messages for Either to include `left`/`right`.
301* Fix missing quotes surrounding time encodings.
303* Fix #293: Type error in TH when using `omitNothingFields = True`.
307* Various updates to support GHC 8.
312## Performance improvements
314* Direct encoding via the new `toEncoding` method is over 2x faster
315 than `toJSON`. (You must write or code-gen a `toEncoding`
316 implementation to unlock this speedup. See below for details.)
318* Improved string decoding gives a 12% speed win in parsing
319 string-heavy JSON payloads (very common).
321* Encoding and decoding of time-related types are 10x faster (!!) as a
322 result of bypassing `Data.Time.Format` and the arbitrary-precision
325* When using `toEncoding`, `[Char]` can be encoded without a conversion to
326 `Text`. This is fast and efficient.
328* Parsing into an `Object` is now 5% faster and more
329 allocation-efficient.
331## SUBTLE API CHANGES, READ CAREFULLY
333With the exception of long-deprecated code, the API changes below
334**should be upwards compatible** from older versions of `aeson`. If you run
335into upgrade problems, please file an issue with details.
337* The `ToJSON` class has a new method, `toEncoding`, that allows
338 direct encoding from a Haskell value to a lazy bytestring without
339 construction of an intermediate `Value`.
341 The performance benefits of direct encoding are significant: more
342 than 2x faster than before, with less than 1/3 the memory usage.
344 To preserve API compatibility across upgrades from older versions of
345 this library, the default implementation of `toEncoding` uses
346 `toJSON`. You will *not* see any performance improvement unless you
347 write an implementation of `toEncoding`, which can be very simple:
350 instance ToJSON Coord where
351 toEncoding = genericToEncoding defaultOptions
354 (Behind the scenes, the `encode` function uses `toEncoding` now, so
355 if you implement `toEncoding` for your types, you should see a
356 speedup immediately.)
358 If you use Template Haskell or GHC Generics to auto-generate your
359 `ToJSON` instances, you'll benefit from fast toEncoding
360 implementations for free!
362* When converting from a `Value` to a target Haskell type, `FromJSON`
363 instances now provide much better error messages, including a
364 complete JSON path from the root of the object to the offending
365 element. This greatly eases debugging.
367* It is now possible to use Template Haskell to generate `FromJSON`
368 and `ToJSON` instances for types in data families.
370* If you use Template Haskell or generics, and used to use the
371 `camelTo` function to rename fields, the new `camelTo2` function is
372 smarter. For example, `camelTo` will rename `CamelAPICase` to
373 `camelapi_case` (ugh!), while `camelTo2` will map it to
374 `camel_api_case` (yay!).
376* New `ToJSON` and `FromJSON` instances for the following time-related
377 types: `Day`, `LocalTime`.
379* `FromJSON` `UTCTime` parser accepts the same values as for `ZonedTime`,
380 but converts any time zone offset into a UTC time.
382* The `Result` type is now an instance of `Foldable` and `Traversable`.
384* The `Data.Aeson.Generic` module has been removed. It was deprecated in
387* GHC 7.2 and older are no longer supported.
389* The instance of `Monad` for the `Result` type lacked an implementation
390 of `fail` (oops). This has been corrected.
392* Semantics of `(.:?)` operator are changed. It's doesn't anymore accept
393 present `Null` value.
395* Added `(Foldable t, ToJSON a) => ToJSON (t a)` overlappable instance.
396 You might see `No instance for (Foldable YourPolymorphicType) arising from a
397 use of ‘.=’` -errors due this change.
401* A stray export of `encodeToBuilder` got away!
405* The `json` and `json'` parsers are now synonyms for `value` and
406 `value'`, in conformance with the looser semantics of RFC 7159.
408* Renamed `encodeToByteStringBuilder` to the more compact
413* The dependency on the `unordered-containers` package was too lax,
414 and has been corrected.
418* Encoding a `Scientific` value with a huge exponent is now handled
419 efficiently. (This would previously allocate a huge
420 arbitrary-precision integer, potentially leading to a denial of
423* Handling of strings that contain backslash escape sequences is
424 greatly improved. For a pathological string containing almost a
425 megabyte of consecutive backslashes, the new implementation is 27x
426 faster and uses 42x less memory.
428* The `ToJSON` instance for `UTCTime` is rendered with higher
429 (picosecond) resolution.
431* The `value` parser now correctly handles leading whitespace.
433* New instances of `ToJSON` and `FromJSON` for `Data.Sequence` and
434 `Data.Functor.Identity`. The `Value` type now has a `Read` instance.
436* `ZonedTime` parser ordering now favours the standard `JSON` format,
437 increasing efficiency in the common case.
439* Encoding to a `Text.Builder` now escapes `'<'` and `'>'` characters,
444* Fix `ToJSON` instance for 15-tuples (see #223).
452* Add `ToJSON` and `FromJSON` instances for tuples of up to 15
457* Major compiler and library compatibility changes: we have dropped
458 support for GHC older than 7.4, `text` older than 1.1, and
459 `bytestring` older than 0.10.4.0. Supporting the older versions had
460 become increasingly difficult, to the point where it was no longer
465* The performance of encoding to and decoding of bytestrings have both
466 improved by up to 2x, while also using less memory.
468* New dependency: the `scientific` package lets us parse floating point
469 numbers more quickly and accurately.
471* `eitherDecode`, `decodeStrictWith`: fixed bugs.
473* Added `FromJSON` and `ToJSON` instances for `Tree` and `Scientific`.
475* Fixed the `ToJSON` instances for `UTCTime` and `ZonedTime`.
479* Much improved documentation.
481* Angle brackets are now escaped in JSON strings, to help avoid XSS
484* Fixed up handling of nullary constructors when using generic
487* Added `ToJSON`/`FromJSON` instances for:
490 * ISO-8601 dates: `UTCTime`, `ZonedTime`, and `TimeZone`
492* Added accessor functions for inspecting `Value`s.
494* Added `eitherDecode` function that returns an error message if
499* This release introduces a slightly obscure, but
500 backwards-incompatible, change.
502 In the generic APIs of versions 0.4 and 0.5, fields whose names
503 began with a `"_"` character would have this character removed. This
504 no longer occurs, as it was both buggy and surprising
505 (https://github.com/bos/aeson/issues/53).
507* Fixed a bug in generic decoding of nullary constructors
508 (https://github.com/bos/aeson/issues/62).
512* When used with the UTF-8 encoding performance improvements
513 introduced in version 0.11.1.12 of the `text` package, this release
514 improves `aeson`'s JSON encoding performance by 33% relative to
517 As part of achieving this improvement, an API change was necessary.
518 The `fromValue` function in the `Data.Aeson.Encode` module now uses
519 the `text` package's `Builder` type instead of the `blaze-builder`
520 package's `Builder` type.
524* The new `decode` function complements the longstanding `encode`
525 function, and makes the API simpler.
527* New examples make it easier to learn to use the package
528 (https://github.com/bos/aeson/tree/master/examples).
532 `aeson`'s support for data-type generic programming makes it
533 possible to use JSON encodings of most data types without writing
534 any boilerplate instances.
536 Thanks to Bas Van Dijk, `aeson` now supports the two major schemes
537 for doing datatype-generic programming:
539 * the modern mechanism, built into GHC itself
540 (http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html)
542 * the older mechanism, based on SYB (aka "scrap your
545 The modern GHC-based generic mechanism is fast and terse: in fact,
546 its performance is generally comparable in performance to
547 hand-written and TH-derived `ToJSON` and `FromJSON` instances. To
548 see how to use GHC generics, refer to `examples/Generic.hs`.
550 The SYB-based generics support lives in `Data.Aeson.Generic` and is
551 provided mainly for users of GHC older than 7.2. SYB is far slower
552 (by about 10x) than the more modern generic mechanism. To see how
553 to use SYB generics, refer to `examples/GenericSYB.hs`.
555* We switched the intermediate representation of JSON objects from
556 `Data.Map` to `Data.HashMap` which has improved type conversion
559* Instances of `ToJSON` and `FromJSON` for tuples are between 45% and 70%
564 This version of aeson makes explicit the decoupling between
565 *identifying* an element of a JSON document and *converting* it to
566 Haskell. See the `Data.Aeson.Parser` documentation for details.
568 The normal `aeson` `decode` function performs identification
569 strictly, but defers conversion until needed. This can result in
570 improved performance (e.g. if the results of some conversions are
571 never needed), but at a cost in increased memory consumption.
573 The new `decode'` function performs identification and conversion
574 immediately. This incurs an up-front cost in CPU cycles, but
575 reduces reduce memory consumption.
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