maml-ast

AST parser for the MAML data format. Produces a full abstract syntax tree with node types, source positions, and comment preservation — designed for building formatters, linters, codemods, and editor tooling.

For a simpler parser that returns plain JavaScript values, see maml.js.

• Full AST with discriminated union node types
• Source positions (offset, line, column) on every node
• Comments preserved and attached to nodes
• print() reconstructs source from AST, including comments
• Zero dependencies, ESM first
• Works in Node.js, Deno, Bun and browsers

Installation

npm install maml-ast

Usage

Parsing

import { parse, print, toValue } from 'maml-ast'

const doc = parse(`{
  # Database config
  host: "localhost"
  port: 5432
}`)

Printing

print() reconstructs MAML source from an AST, preserving comments:

print(doc)
// {
//   # Database config
//   host: "localhost"
//   port: 5432
// }

Converting to plain values

toValue() strips AST metadata and returns plain JavaScript values:

toValue(doc)  // { host: 'localhost', port: 5432 }

AST Node Types

Every node has a type discriminant and a span with start/end positions.

| Node Type | type | value | raw | |------------|---------------|--------------------|-------| | String | 'String' | string | yes | | Raw String | 'RawString' | string | yes | | Integer | 'Integer' | number \| bigint | yes | | Float | 'Float' | number | yes | | Boolean | 'Boolean' | boolean | — | | Null | 'Null' | null | — | | Object | 'Object' | properties | — | | Array | 'Array' | elements | — |

Keys

Object keys are either IdentifierKey (type: 'Identifier') for bare keys like foo, or StringNode ( type: 'String') for quoted keys like "foo bar".

Comments

Comments are attached to the nearest node:

• Property.leadingComments — comments on lines before the property
• Property.trailingComment — comment on the same line after the value
• ObjectNode.innerComments / ArrayNode.innerComments — comments inside an empty container or after the last entry
• Document.leadingComments / Document.trailingComments — comments before/after the root value

Document

parse() returns a Document node wrapping the root value:

interface Document {
  type: 'Document'
  value: ValueNode
  leadingComments: CommentNode[]
  trailingComments: CommentNode[]
  span: Span
}

License

MIT