add Parser && YamlLoader

LICENSE

@@ -24,13 +24,12 @@ SOFTWARE.
 
 This project contains code from the following third-party project, which is licensed under the MIT License:
 
-denoland/std
-
 The original license is as follows:
 
-MIT License
+The MIT License (MIT)
 
-Copyright 2018-2022 the Deno authors.
+Copyright (c) 2015 Chen Yuheng
+Copyright (c) 2023 Ethiraric
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.mbt.md

@@ -1,5 +1,5 @@
 # YAML
 
-A comprehensive YAML parsing and stringifying library for MoonBit, supporting YAML 1.2.
+A simple YAML parsing and stringifying library for MoonBit, support a simplified YAML subset which can be convert to JSON.
 
 This library is ported from yaml-rust2.

moon.mod.json

@@ -2,7 +2,7 @@
   "name": "myfreess/yaml",
   "version": "0.1.0",
   "readme": "README.md",
-  "repository": "",
+  "repository": "https://github.com/moonbit-community/yaml.mbt",
   "license": "MIT",
   "keywords": [],
   "description": "",

src/error.mbt

@@ -0,0 +1,6 @@
+///|
+pub suberror YamlError {
+  /// - `mark`: The position at which the error happened in the source.
+  /// - `info`: Human-readable details about the error.
+  YamlError(mark~ : Marker, info~ : String)
+} derive(Show)

src/event.mbt

@@ -0,0 +1,92 @@
+///|
+pub enum Event {
+  /// Event generated at the very beginning of parsing.
+  StreamStart
+  /// Last event that will be generated by the parser. Signals EOF.
+  StreamEnd
+  /// The YAML start document directive (`---`).
+  DocumentStart
+  /// The YAML end document directive (`...`).
+  DocumentEnd
+  /// A YAML Alias.
+  /// - id : The anchor ID the alias refers to.
+  Alias(id~ : Int)
+  /// Value, style, anchor id, tag
+  Scalar(value~ : String, style~ : TScalarStyle, id~ : Int, tag~ : Tag?)
+  /// The start of a YAML sequence (array).
+  /// - id : The anchor ID of the start of the sequence.
+  /// - tag : An optional tag
+  SequenceStart(id~ : Int, tag~ : Tag?)
+  /// The end of a YAML sequence (array).
+  SequenceEnd
+  /// The start of a YAML mapping (object, hash).
+  /// - id : The anchor ID of the start of the mapping.
+  /// - tag : An optional tag
+  MappingStart(id~ : Int, tag~ : Tag?)
+  /// The end of a YAML mapping (object, hash).
+  MappingEnd
+} derive(Eq, Show)
+
+///|
+fn Event::empty_scalar() -> Event {
+  Event::Scalar(value="", style=TScalarStyle::Plain, id=0, tag=None)
+}
+
+///|
+fn Event::empty_scalar_with_anchor(anchor : Int, tag : Tag?) -> Event {
+  Event::Scalar(value="", style=TScalarStyle::Plain, id=anchor, tag~)
+}
+
+///|
+/// Trait to be implemented in order to use the low-level parsing API.
+///
+/// The low-level parsing API is event-based (a push parser), calling [`EventReceiver::on_event`]
+/// for each YAML [`Event`] that occurs.
+/// The [`EventReceiver`] trait only receives events. In order to receive both events and their
+/// location in the source, use [`MarkedEventReceiver`]. Note that [`EventReceiver`]s implement
+/// [`MarkedEventReceiver`] automatically.
+///
+/// # Event hierarchy
+/// The event stream starts with an [`Event::StreamStart`] event followed by an
+/// [`Event::DocumentStart`] event. If the YAML document starts with a mapping (an object), an
+/// [`Event::MappingStart`] event is emitted. If it starts with a sequence (an array), an
+/// [`Event::SequenceStart`] event is emitted. Otherwise, an [`Event::Scalar`] event is emitted.
+///
+/// In a mapping, key-values are sent as consecutive events. The first event after an
+/// [`Event::MappingStart`] will be the key, and following its value. If the mapping contains no
+/// sub-mapping or sub-sequence, then even events (starting from 0) will always be keys and odd
+/// ones will always be values. The mapping ends when an [`Event::MappingEnd`] event is received.
+///
+/// In a sequence, values are sent consecutively until the [`Event::SequenceEnd`] event.
+///
+/// If a value is a sub-mapping or a sub-sequence, an [`Event::MappingStart`] or
+/// [`Event::SequenceStart`] event will be sent respectively. Following events until the associated
+/// [`Event::MappingStart`] or [`Event::SequenceEnd`] (beware of nested mappings or sequences) will
+/// be part of the value and not another key-value pair or element in the sequence.
+///
+/// For instance, the following yaml:
+/// ```yaml
+/// a: b
+/// c:
+///   d: e
+/// f:
+///   - g
+///   - h
+/// ```
+/// will emit (indented and commented for lisibility):
+/// ```text
+/// StreamStart, DocumentStart, MappingStart,
+///   Scalar("a", ..), Scalar("b", ..)
+///   Scalar("c", ..), MappingStart, Scalar("d", ..), Scalar("e", ..), MappingEnd,
+///   Scalar("f", ..), SequenceStart, Scalar("g", ..), Scalar("h", ..), SequenceEnd,
+/// MappingEnd, DocumentEnd, StreamEnd
+/// ```
+pub trait EventReceiver {
+  /// Handler called for each YAML event that is emitted by the parser.
+  on_event(Self, event : Event) -> Unit
+}
+
+///|
+pub trait MarkedEventReceiver {
+  on_event(Self, event : Event, _mark : Marker) -> Unit
+}