Converting Between JSON and MAML on the Command Line

MAML is a minimal config format: JSON without mandatory commas and key quotes, plus comments and multiline strings. Fx reads MAML as input and writes it with the built-in MAML.stringify.

Convert MAML to JSON

Given config.maml:

{
  # Server settings
  name: "my-app"
  port: 8080
  tags: ["web", "api"]
  motd: """
Welcome!
Have a nice day.
"""
}

Pass the . argument to print it as pretty JSON:

fx config.maml .

{
  "name": "my-app",
  "port": 8080,
  "tags": [
    "web",
    "api"
  ],
  "motd": "Welcome!\nHave a nice day.\n"
}

Files ending in .maml are detected by extension. With stdin, use the --maml flag:

cat config.maml | fx --maml .

Save the result with fx config.maml . > config.json. Run fx config.maml without arguments to explore the file interactively.

Query MAML

Everything that works on JSON works on MAML:

fx config.maml .port
fx config.maml '.tags.join(", ")'

Convert JSON to MAML

Pipe JSON through MAML.stringify:

fx package.json MAML.stringify

{
  name: "my-app"
  version: "1.0.0"
  scripts: {
    test: "node test.js"
  }
}

Keys are quoted only when needed, and arrays and objects are written one item per line.

Parse MAML stored in a string

When a JSON field holds MAML text, decode it with MAML.parse:

echo '{"config": "{a: 1, b: [2, 3]}"}' | fx .config MAML.parse

Notes

• Key order is preserved.
• Comments are dropped, since JSON has no comments.
• Numbers keep their exact text, so 1.0 stays 1.0 and long decimals keep all digits.
• MAML integers are 64-bit; a larger integer is a syntax error.
• Duplicate keys are a syntax error.