elm-decode-runner

CLI tool to run an Elm decoder on JSON input from stdin.

Installation

Using npm

npm install -g elm-decode-runner

Using Nix

You can run elm-decode-runner directly from GitHub without installing:

echo '{"name":"Alice","age":30}' | nix run github:pete-murphy/node-elm-decode-runner -- Example.User.decoder

Usage

Direct Decoder Usage

echo '{"name":"Alice","age":30}' | elm-decode-runner Example.User.decoder

Discover Available Decoders

elm-decode-runner --discover

Interactive Decoder Selection (with fzf)

echo '{"name":"Alice","age":30}' | elm-decode-runner --discover

This will:

1. Parse and validate your JSON input
2. Discover all available decoders in your project
3. Launch fzf to let you interactively select a decoder
4. Run the selected decoder on your JSON input

This tool makes it easy to test Elm decoders from the command line by:

1. Taking JSON input from stdin
2. Running it through the specified Elm decoder
3. Printing the result to stdout

Requirements

• Must be run in an Elm project directory (with valid elm.json)
• The specified decoder must be found in the module path
• For interactive mode: fzf must be installed (optional)

Arguments

• elm-decode-runner <Module.Path.decoderName> - Run a specific decoder
• elm-decode-runner --discover - List all available decoders
• echo '{}' | elm-decode-runner --discover - Interactive decoder selection

Where:

• Module.Path is the Elm module path (e.g., Example.User)
• decoderName is the name of the decoder function (e.g., decoder)

Examples

Success case

❯ curl -s https://jsonplaceholder.typicode.com/todos/1 | elm-decode-runner Example.Todo.decoder
{ completed = False, id = 1, title = "delectus aut autem", userId = 1 }

Discovery example

❯ elm-decode-runner --discover
Example.Todo.decoder
Example.User.userDecoder
Example.User.adminDecoder
Utils.Config.settingsDecoder

Interactive example

❯ echo '{"id":1,"name":"Alice"}' | elm-decode-runner --discover
# Opens fzf with list of decoders, after selection:
{ id = 1, name = "Alice" }

Failure case

❯ echo '{"name":"Alice","age":30}' | elm-decode-runner Example.User.decoder
Problem with the given value:

{
        "name": "Alice",
        "age": 30
    }

Expecting an OBJECT with a field named `email`

License

ISC