purescript-json-codecs

A unidirectional value-based JSON codec library.

Whether this is more performant than other options is still being clarified. See the benchmarks.

Design

See DESIGN.md for the reasoning behind this library's design. The rest of this section covers my goals and where I'm at in that process.

Address gripes with other JSON codec libraries:

simple-json:
- I don't want to have to fork or copy the repo to benefit from it / change various type class instances.
- I don't want to use your information-poor error type, NonEmptyList ForeignError
argonaut-codec/codec-argonaut:
- I don't want to use your information-poor error type, JsonDecodeError

Improve error messages:

show me all failures, not just the first one
on type mismatch errors, show me what you expected AND got, not just what was expected
allow me to write custom error messages

Provide record syntax I enjoy using

See snapshots

Sample Json decode message:

Given the following code...

toNel :: forall a. Array a -> NonEmptyList a
toNel = unsafePartial fromJust <<< NEL.fromList <<< List.fromFoldable

printDecodeError
    $ AtKey "some-key"
    $ AtIndex 0
    $ AccumulateError $ toNel
      [ AccumulateError $ toNel [ AtIndex 0 $ DecodeError "Error0" ]
      , AtKey "bar" $ AtIndex 1 $ DecodeError "Error1"
      , AtKey "baz" $ accumulateErrors
          (AtIndex 0 $ DecodeError "Error2")
          (AtIndex 1 $ DecodeError "Error3")
      , AccumulateError $ toNel
          [ AccumulateError $ toNel [ AtIndex 1 $ DecodeError "Error4" ]
          , AtKey "last1" $ DecodeError "Error5"
          , AtKey "last2" $ DecodeError "Error6"
          ]
      , AccumulateError $ toNel
          [ AtKey "last3" $ DecodeError "Error7"
          , AtKey "last4" $ DecodeError "Error8"
          , AccumulateError $ toNel [ AtIndex 2 $ DecodeError "Error9" ]
          ]
      , AccumulateError $ toNel
          [ AccumulateError $ toNel
              [ AtKey "a" $ DecodeError "Error10"
              , AtKey "b" $ DecodeError "Error11"
              , AtKey "c" $ DecodeError "Error12"
              ]
          , AccumulateError $ toNel
              [ AtKey "x" $ DecodeError "Error13"
              , AtKey "y" $ DecodeError "Error14"
              , AtKey "z" $ DecodeError "Error15"
              ]
          ]
      ]

the error message printed is the following. Indented values are all of the errors that happened under the given JSON path:

ROOT."some-key"[0]
  [0] - Error0
  ."bar"[1] - Error1
  ."baz"
    [1] - Error3
    [0] - Error2
  [1] - Error4
  ."last1" - Error5
  ."last2" - Error6
  ."last3" - Error7
  ."last4" - Error8
  [2] - Error9
  ."a" - Error10
  ."b" - Error11
  ."c" - Error12
  ."x" - Error13
  ."y" - Error14
  ."z" - Error15

purescript-json-codecs

Design

Sample Json decode message:

License