bs-json
Experimental JSON encode/decode library for BuckleScript.
NOTE: NPM package has moved to @glennsl/bs-json
. Remember to update both package.json
AND bsconfig.json
.
The Decode module in particular provides a basic set of decoder functions to be composed into more complex decoders. A
decoder is a function that takes a Js.Json.t
and either returns a value of the desired type if successful or raises a
DecodeError
exception if not. Other functions accept a decoder and produce another decoder. Like array
, which when
given a decoder for type t
will return a decoder that tries to produce a value of type t array
. So to decode an
int array
you combine Json.Decode.int
with Json.Decode.array
into Json.Decode.(array int)
. An array of arrays of
ints? Json.Decode.(array (array int))
. Dict containing arrays of ints? Json.Decode.(dict (array int))
.
Example
(* OCaml *)type line = { start: point; end_: point; thickness: int option}and point = { x: float; y: float} module Decode = struct let point json = let open! Json.Decode in { x = json |> field "x" float; y = json |> field "y" float } let line json = Json.Decode.{ start = json |> field "start" point; end_ = json |> field "end" point; thickness = json |> optional (field "thickness" int) }end let data = {| { "start": { "x": 1.1, "y": -0.4 }, "end": { "x": 5.3, "y": 3.8 }} |} let line = data |> Json.parseOrRaise |> Decode.line
/* Reason */type line = { start: point, end_: point, thickness: option(int)}and point = { x: float, y: float}; module Decode = { let point = json => Json.Decode.{ x: json |> field("x", float), y: json |> field("y", float) }; let line = json => Json.Decode.{ start: json |> field("start", point), end_: json |> field("end", point), thickness: json |> optional(field("thickness", int)) };}; let data = {| { "start": { "x": 1.1, "y": -0.4 }, "end": { "x": 5.3, "y": 3.8 }} |}; let line = data |> Json.parseOrRaise |> Decode.line;
See examples for more.
Installation
npm install --save bs-json
Then add bs-json
to bs-dependencies
in your bsconfig.json
:
... "bs-dependencies": "bs-json"
Documentation
API
For the moment, please see the interface files:
Writing custom decoders and encoders
If you look at the type signature of Js.Decode.array
, for example, you'll see it takes an 'a decoder
and returns an
'a array decoder
. 'a decoder
is just an alias for Js.Json.t -> 'a
, so if we expand the type signature of array
we'll get (Js.Json.t -> 'a) -> Js.Json.t -> 'a array
. We can now see that it is a function that takes a decoder and
returns a function, itself a decoder. Applying the int
decoder to array
will give us an int array decoder
, a
function Js.Json.t -> int array
.
If you've written a function that takes just Js.Json.t
and returns user-defined types of your own, you've already been
writing composable decoders! Let's look at Decode.point
from the example above:
let point json = let open! Json.Decode in { x = json |> field "x" float; y = json |> field "y" float }
This is a function Js.Json.t -> point
, or a point decoder
. So if we'd like to decode an array of points, we can just
pass it to Json.Decode.array
to get a point array decoder
in return.
Builders
To write a decoder builder like Json.Decode.array
we need to take another decoder as an argument, and thanks to
currying we just need to apply it where we'd otherwise use a fixed decoder. Say we want to be able to decode both
int point
s and float point
s. First we'd have to parameterize the type:
type 'a point = { x: 'a, y: 'a}
Then we can change our point
function from above to take and use a decoder argument:
let point decodeNumber json = let open! Json.Decode in { x = json |> field "x" decodeNumber; y = json |> field "y" decodeNumber }
And if we wish we can now create aliases for each variant:
let intPoint = point Json.Decode.intlet floatPoint = point Json.Decode.float
Encoders
Encoders work exactly the same way, just in reverse. 'a encoder
is just an alias for 'a -> Js.Json.t
, and this also
transfers to composition: 'a encoder -> 'a array encoder
expands to ('a -> Js.Json.t) -> 'a array -> Js.Json.t
.
Changes
1.0.1
- Moved repository from
reasonml-community/bs-json
toglennsl/bs-json
- Renamed NPM package from
bs-json
to@glennsl/bs-json
1.0.0
- Replaced
Json.Encoder.array
withJson.Encode.arrayOf
renamed toarray
. DeprecatedarrayOf
alias. - Added
Json.parse
,Json.parseOrRaise
,Json.stringify
- Added
date
encoder and decoder - Added
tuple2
/tuple3
/tuple4
encoders and decoders - Fixed bug where js integers > 32-bit were rejected as integers by Json.Decode.int (#15)
0.2.4
- Added
Json.Encode.bool
- Added
Json.Encode.pair
- Added
Json.Encode.withDefault
- Added
Json.Encode.nullable
- Added
Json.Encode.arrayOf
- Added
Json.Encode.jsonArray
as replacement forJson.Encode.array
- Deprecated
Json.Encode.array
0.2.3
- Fixed embarrassing bug where an API was used that isn't available on IE (honestly more embarrassed on behalf of IE though)
0.2.2
- Added
Json.Decode.pair
0.2.1
- Added
Json.Encode.list
0.2.0
- Breaking: Renamed
Json.Encode.object_
toJson.Encode.dict
- Added
Json.Encode.object_
taking a list of properties instead of a Json.Dict.t as before