json 🐑

Work with JSON in Gleam!

Installation

Erlang/OTP 27.0 or higher is required when targeting Erlang. To use earlier versions of Erlang/OTP use version 1.0.1 of this package.

Add this package to your Gleam project.

# Erlang version <= OTP26
gleam add gleam_json@1

# Erlang version >= OTP27
gleam add gleam_json@2

Encoding

import myapp.{type Cat}
import gleam/json

pub fn cat_to_json(cat: Cat) -> String {
  json.object([
    #("name", json.string(cat.name)),
    #("lives", json.int(cat.lives)),
    #("flaws", json.null()),
    #("nicknames", json.array(cat.nicknames, of: json.string)),
  ])
  |> json.to_string
}

Parsing

JSON is parsed into a Dynamic value which can be decoded using the gleam/dynamic/decode module from the Gleam standard library.

import myapp.{Cat}
import gleam/json
import gleam/dynamic/decode

pub fn cat_from_json(json_string: String) -> Result(Cat, json.DecodeError) {
  let cat_decoder = {
    use name <- decode.field("name", of: decode.string)
    use name <- decode.field("lives", of: decode.int)
    use name <- decode.field("nicknames", of: decode.list(decode.string))
    decode.success(Cat(name:, lives:, nicknames:))
  }
  json.parse(from: json_string, using: cat_decoder)
}