decoder

JSON decoders for @derive(decoder):

import bea_codecs/json/decoder

@derive(decoder)
pub type Credentials {
  Credentials(username: String, password: String)
}

credentials = decoder.from_json(body, Credentials.decoder())?

A derived decoder is a plain decode.Decoder from the standard library, so it works with json.parse, decode.run on any Dynamic, and every Gleam library that takes decoders.

The conventions are this module’s, not the compiler’s: a record is an object with a key per field label; a field whose decoder accepts null (an Option) may also be left out; an integer is accepted where a float is expected; errors are the standard library’s, with the path to the failing value.

Values

bool

</>

pub fn bool() -> decode.Decoder(Bool)

dict

</>

pub fn dict(
  keys: decode.Decoder(k),
  values: decode.Decoder(v),
) -> decode.Decoder(dict.Dict(k, v))

done

</>

pub fn done(value: r) -> decode.Decoder(r)

field

</>

pub fn field(
  label: String,
  of: decode.Decoder(a),
  get: fn(r) -> a,
  next: fn(a) -> decode.Decoder(r),
) -> decode.Decoder(r)

One field, under its label. Missing is the same as null: fine when the field’s decoder accepts null, a “missing field” error otherwise.

float

</>

pub fn float() -> decode.Decoder(Float)

JSON doesn’t tell 1 from 1.0: both are fine for a Float.

from_json

</>

pub fn from_json(
  text: String,
  decoder: decode.Decoder(a),
) -> Result(a, json.DecodeError)

int

</>

pub fn int() -> decode.Decoder(Int)

list

</>

pub fn list(of: decode.Decoder(a)) -> decode.Decoder(List(a))

option

</>

pub fn option(
  of: decode.Decoder(a),
) -> decode.Decoder(option.Option(a))

null is None.

record

</>

pub fn record(
  constructor: String,
  fields: fn() -> decode.Decoder(r),
) -> decode.Decoder(r)

A record is decoded from its fields.

string

</>

pub fn string() -> decode.Decoder(String)