funicular - composable JSON parsing for ReScript

• easily composable using builtin primitives, or extend with your own
• write typesafe and idiomatic parsers
• meaningful error output with result types

Install

1. Install from npm

npm i rescript-funicular -S # yarn add rescript-funicular

2. Add to your bsconfig.json

  "bs-dependencies": [
    ...
    "rescript-funicular",
  ]

Example

Define your type:

type customer = {
  customerNo: int,
  name: string,
  orders: array<order>,
}

And write a decoder function:

// Write decoder functions that translate the JSON structure into your fields
let decodeCustomer = value => {
  open Funicular.Decode

  // first decode the value as an object
  let o = value->object_

  // extract and parse each field of the object using the relevant decoder
  let customerNo = o->field("customerNo", integer)
  let name = o->field("name", string)
  // `decodeOrder` is a custom decoder for the `order` type
  let orders = o->field("orders", array(decodeOrder)) 

  // Use `rmap()` to wrap your builder function, and then feed in each parameter with `v()`
  rmap((customerNo, name, orders) => {customerNo: customerNo, name: name, orders: orders})
  ->v(customerNo)
  ->v(name)
  ->v(orders)
}

Use the Funicular.Decode.parse function to parse your string, passing in your decoder:

// Parse with your custom decoder function for the root object
let customerString = `{"customerNo": 20, "name": "Chris", "orders": [] }`
let myCustomer = Funicular.Decode.parse(customerString, decodeCustomer);

Encoding is simpler - a straight type conversion without the error-handling overhead:

let encodeCustomer = val => {
  open Funicular.Encode
  object_([
    ("customerNo", integer(val.customerNo)),
    ("name", string(val.name)),
    ("orders", array(val.orders, encodeOrder)),
  ])
}