Elm:
Working with YAML

How to:

To handle YAML in Elm, you typically need to convert YAML to JSON outside of Elm and then use Elm’s built-in JSON decoder functionality to work with the data. While this approach requires an additional conversion step, it leverages Elm’s strong type system to ensure data integrity. Popular tools for YAML to JSON conversion include online converters or backend services. Once you have JSON, you can use Elm’s Json.Decode module to work with the data.

First, assuming you have the following YAML data:

person:
  name: Jane Doe
  age: 30

Convert it to JSON format:

{
  "person": {
    "name": "Jane Doe",
    "age": 30
  }
}

Then, define your Elm model and decoder:

module Main exposing (..)

import Html exposing (text)
import Json.Decode as Decode

type alias Person =
    { name : String
    , age : Int
    }

personDecoder : Decode.Decoder Person
personDecoder =
    Decode.map2 Person
        (Decode.field "name" Decode.string)
        (Decode.field "age" Decode.int)

To use this decoder for converting JSON to an Elm type:

import Json.Decode as Decode

jsonString = 
    """
    {
      "person": {
        "name": "Jane Doe",
        "age": 30
      }
    }
    """

decodeResult = Decode.decodeString (Decode.field "person" personDecoder) jsonString

main =
    case decodeResult of
        Ok person ->
            Html.text ("Hello, " ++ person.name ++ "!")
            
        Err _ ->
            Html.text "An error occurred while decoding."

Output (rendered in an Elm application):

Hello, Jane Doe!

This approach ensures that you can work with YAML data in Elm by utilizing JSON as an intermediary format, taking advantage of Elm’s robust type system and JSON decoding capabilities to safely and effectively manipulate external data.