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rescript-json-combinators

Combinator library for JSON decoding and encoding.

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Example

type point = {
  x: int,
  y: int,
}

type polyline = {
  points: array<point>,
  thickness: option<int>,
}

module Decode = {
  open Json.Decode

  let point = object(field => {
    x: field.required(. "x", int),
    y: field.required(. "y", int),
  })

  let polyline = object(field => {
    points: field.required(. "points", array(point)),
    thickness: field.optional(. "thickness", int),
  })
}

let data = `{
  "points": [
    { "x": 1, "y": -4 },
    { "x": 5, "y": 8 }
  ]
}`

let _ = data->Js.Json.parseExn->Json.decode(Decode.polyline)->Js.log

See examples for more.

Installation

npm install --save @glennsl/rescript-json-combinators

Then add @glennsl/rescript-json-combinators to bs-dependencies in your bsconfig.json:

 {
   "bs-dependencies": [
+    "@glennsl/rescript-json-combinators"
   ]
 }

Optionally, add this to automatically open the library in order to use Json.Encode and Json.Decode directly:

 {
   "bsc-flags": [
+    "-open JsonCombinators",
   ]
 }

Differences from bs-json

rescript-json-combinators is the spriritual successor of bs-json. It was rewritten from scratch and not intended to be backwards compatible. And while for the most part is does share the same design principles,there are also some notable differences:

  • Decoders have been made abstract. While the internal representation is still the same, a function that takes a Js.Json.t and returns either the decoded value or raises an exception, they can no longer be called directly. Instead they have to be run via Decode.decode. This is in order to ensure that the DecodeError exceptions don't leak and returns a result instead. Custom decoders can still be created with Decode.custom.

  • A new object decoder has been added, and while it's still possible to decode fields individually in a custom decoder, this addresses a couple ergonomic problems with that approach, such as distinguishing between a field missing and having the wrong type, and the over-use and under-encapsulation of custom decoders.

  • Uncurrying and raw javascript is used in some places to improve performance. For the most part this isn't visible to the end user because decoders can no longer be called directly. There are a couple exceptions however, such as field decoders inside the object deocder, and map.

Documentation

API

For the moment, please see the interface files:

License

This work is dual-licensed under LGPL 3.0 and MPL 2.0. You can choose between one of them if you use this work.

Please see LICENSE.LGPL-3.0 and LICENSE.MPL-2.0 for the full text of each license.

SPDX-License-Identifier: LGPL-3.0 OR MPL-2.0

Changes

1.4.0

  • explicitly curried encode combinators to reduce breakage in rescript 11 uncurried mode
  • updated examples to rescript 11

1.3.0

  • add Decode.indirect to help with decoding recursive data structures

1.2.0

  • add Decode.flatMap

1.1.0

  • recript v11-compatible formatting (#3)

1.0.0

Initial release