MoonBit JSONPath

MoonBit JSONPath is a small JSONPath parser and evaluator written in MoonBit. It targets the core query patterns described by RFC 9535 and integrates directly with moonbitlang/core/json.

The project is maintained for the MoonBit Open Source Ecosystem Competition 2026. The public repositories are:

• GitHub: https://github.com/ppyj663/moon-jsonpath
• GitLink: https://gitlink.org.cn/ppyj663/moon-jsonpath

Features

• Parses JSONPath strings into a compact MoonBit AST.
• Evaluates queries against Json values from moonbitlang/core/json.
• Supports root, child, bracket child, recursive descendant, wildcard, array index, negative index, slicing, union, and filter selectors.
• Supports escape sequences and unicode escapes in bracket name selectors.
• Ships focused unit tests and a runnable CLI example.
• Uses the Apache-2.0 license.

Installation

The module name is:

ppyj663/moon-jsonpath

Install the published Mooncakes package from your project root:

moon add ppyj663/moon-jsonpath

Then import it from a package:

import {
  "ppyj663/moon-jsonpath" @jsonpath,
}

Quick Start

let json = @json.parse(
  #|{
  #|  "store": {
  #|    "book": [
  #|      { "title": "Sayings of the Century", "price": 8.95 },
  #|      { "title": "Sword of Honour", "price": 12.99 }
  #|    ]
  #|  }
  #|}
)

match @jsonpath.query(json, "$.store.book[0].title") {
  Ok(values) => println(values[0].stringify())
  Err(message) => println("query failed: \{message}")
}

Run the included example:

moon run cmd/main

Expected output:

query: $.store.book[0].title
matches: 1
"Sayings of the Century"

Supported Syntax

Syntax	Meaning	Example
$	Root node	$
.<name>	Object child selector	$.store.bicycle
['<name>'] or ["<name>"]	Bracket child selector (supports string escapes)	$['store']['book']
.. <name> without the space	Recursive descendant selector	$..price
.* / [*]	Object or array wildcard	$.store.book[*]
[<number>]	Array index (supports negative indices)	$.store.book[-1]
[<start>:<end>:<step>]	Array slicing (supports positive and negative steps)	$.store.book[1:3]
[<sel1>, <sel2>]	Union selector	$.store.book[0, 2]
[?(<expr>)]	Filter selector (supports comparisons, logical AND/OR/NOT)	$.store.book[?(@.price < 10)]

Not yet supported: function extensions.

API

pub fn parse(input : String) -> Result[JSONPath, String]
pub fn evaluate(json : Json, path : JSONPath) -> Array[Json]
pub fn query(json : Json, path_str : String) -> Result[Array[Json], String]

query is the usual entry point. It returns Err(message) for unsupported or malformed JSONPath syntax and returns an empty array when a valid query simply finds no matching node.

Development

moon update
moon fmt --check
moon check --deny-warn
moon test
moon run cmd/main

The repository also contains a GitHub Actions workflow that runs the same verification path on every push and pull request.

Mooncakes package ppyj663/moon-jsonpath version 0.2.0 is published. The release was validated with moon package, moon publish --dry-run, and moon publish.

Competition Closeout

Closeout evidence is tracked in docs/competition/acceptance.md. The one-page project report is report.pdf.

License

This project is released under the Apache License 2.0.