category feedJSONPopular data formatseditdelete







JSON is a very popular format that is used pretty much everywhere. It looks like this:

{
    "name": "John Smith",
    "isAlive": true,
    "age": 25,
    "address": {
        "streetAddress": "21 2nd Street",
        "city": "New York",
        "state": "NY",
        "postalCode": "10021-3100" },
    "phoneNumbers": [
        { "type": "home",
          "number": "212 555-1234" },
        { "type": "mobile",
          "number": "123 456-7890" } ]
}

It supports objects (dictionaries), arrays, strings, numbers, booleans, and null. JSON doesn't distinguish between integers and floating-point numbers, and doesn't provide any way to handle binary data.

Recommendations

Everyone uses aeson. All other libraries are either outdated or experimental.

You might have to use one of the alternative encoders if you really need performance and Aeson isn't enough for you, or you might have to use one of the alternative decoders if you really need constant-space decoding, but those are rare cases.

Aeson doesn't provide pretty-printed JSON out of the box, so use aeson-pretty for that.

TODO

Benchmark various encoders/decoders. Give examples for everything.

Not included

  • easyjson: seems to provide the same parsing model as aeson, has no extra functionality, and only works with base-4.7

  • json-ast: could be useful for some purposes (it's a tiny library providing just the JSON type, nothing else), but hard to categorise here

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aeson (Hackage)
encoder/decoder
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Summary edit summary

Haskell's de-facto standard JSON parsing library.

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  • Widely used and actively developed.
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  • Fast.
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Consedit consquit editing cons
  • Can be rather complicated/non-intuitive to use.
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highjson (Hackage)
encoder/decoder
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Summary edit summary

A fast library that tries to require less boilerplate than aeson (and provides a different parsing model). Use at your own risk.

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Prosedit prosquit editing pros
  • As fast as Aeson (benchmarks).
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  • The same declaration is used to convert to/from JSON – there's no need to write separate ToJSON and FromJSON instances and worry about them accidentally going out of sync.
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Consedit consquit editing cons
  • The library is still work in progress.
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  • There are some examples, but not much documentation.
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json-encoder (Hackage)
encoder
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A fast JSON builder.

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      buffer-builder (Hackage)
      encoder
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      Summary edit summary

      Another fast JSON builder.

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          json-stream (Hackage)
          decoder
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          Summary edit summary

          A fast decoder that tries to do the least amount of work possible (e.g. it skips parsing of unnecessary fields, etc) and can even parse certain JSON structures using constant space.

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          Prosedit prosquit editing pros
          • Compatible with aeson.
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          • Sometimes doesn't tell you when the JSON is malformed (this is by design, tho).
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          json-incremental-decoder (Hackage)
          decoder
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          Summary edit summary

          Another incremental decoder.

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              aeson-parsec-picky (Hackage)
              decoder
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              Summary edit summary

              A JSON parser written in Parsec, can be used instead of the default Aeson parser. Intended for use with human-written JSON (config files, etc) – unlike Aeson's parser, it reports error positions, which is pretty useful.

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              • Compatible with aeson.
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              Consedit consquit editing cons
              • Slower than the default aeson parser.
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              • Disallows trailing spaces, which isn't good if you simply wanted a parser that would be the same as Aeson's parser but with better error reporting.
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