Compositional JSON encode/decode library for BuckleScript.
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))
.
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.
npm install --save @glennsl/bs-json
Then add @glennsl/bs-json
to bs-dependencies
in your bsconfig.json
:
{
...
"bs-dependencies": ["@glennsl/bs-json"]
}
For the moment, please see the interface files:
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 => {
open! Json.Decode;
{
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.
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 point('a) = {
x: 'a,
y: 'a
}
Then we can change our point
function from above to take and use a decoder argument:
let point = (decodeNumber, json) => {
open! Json.Decode;
{
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.int);
let floatPoint = point(Json.Decode.float);
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
.
- Replace usage of
Js.Date.toJSON
withJs.Date.toJSONUsafe
, which is exactly the same, just to avoid deprecation warnings for end users (Thanks Bob!) - Requires
bs-platform
>= 4.0.2
- Removed
Json.Decode.boolean
,Json.Encode.boolean
,Json.Encode.booleanArray
- Requires
bs-platform
>= 3.0.0
- Reverted commits that broke backwards compatibility despite only affecting the implementation
- Deprecated
Json.Decode.boolean
,Json.Encode.boolean
,Json.Encode.booleanArray
- Added
Json.Encode.boolArray
- Added
Json.Encode.char
andJson.Decode.char
- Added "stack traces" to higher-order decoders, making it easier to find the location of an error.
- Moved repository from
reasonml-community/bs-json
toglennsl/bs-json
- Renamed NPM package from
bs-json
to@glennsl/bs-json
- 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)
- 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
- Fixed embarrassing bug where an API was used that isn't available on IE (honestly more embarrassed on behalf of IE though)
- Added
Json.Decode.pair
- Added
Json.Encode.list
- 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