yml2hml — YAML to HML Converter

yml2hml is a standalone tool written in hica that converts YAML files to HML format. It demonstrates how hica handles real-world parsing, recursive data structures, and formatted output.

Run from source

Requires hica and Koka:

hica run programs/yml2hml.hc -- input.yml

Or build a standalone binary:

hica build programs/yml2hml.hc
./programs/yml2hml input.yml

Usage

$ yml2hml --help
yml2hml 1.0.0 — convert YAML files to HML format

USAGE: yml2hml [OPTIONS] <input> [output]

OPTIONS:
  -h, --help            Show this help
      --version         Show version

ARGS:
  <input>               YAML file to convert (required)
  <output>              output HML file (default: stdout)

# Print HML to stdout
yml2hml config.yml

# Write to a file
yml2hml config.yml output.hml

Example

Given a tbdflow configuration file (.tbdflow.yml):

main_branch_name: main
stale_branch_threshold_days: 1
monorepo:
  enabled: false
  project_dirs: []
review:
  enabled: false
  strategy: github-issue
  labels:
    pending: review-pending
    concern: review-concern
    accepted: review-accepted
    dismissed: review-dismissed
radar:
  enabled: true
  level: file
  on_sync: true
  on_commit: off
  ignore_patterns:
  - '*.lock'
  - '*-lock.*'
  - CHANGELOG.md
branch_types:
  feat: feat/
  fix: fix/
  docs: docs/
  chore: chore/
lint:
  conventional_commit_type:
    enabled: true
    allowed_types:
    - feat
    - fix
    - docs
    - refactor
    - test
    - chore

Running yml2hml .tbdflow.yml produces:

main-branch-name: "main"
stale-branch-threshold-days: 1
@monorepo {
    enabled: false
    project-dirs: []
}
@review {
    enabled: false
    strategy: "github-issue"
    @labels {
        pending: "review-pending"
        concern: "review-concern"
        accepted: "review-accepted"
        dismissed: "review-dismissed"
    }
}
@radar {
    enabled: true
    level: "file"
    on-sync: true
    on-commit: false
    ignore-patterns: ["*.lock", "*-lock.*", "CHANGELOG.md"]
}
@branch-types {
    feat: "feat/"
    fix: "fix/"
    docs: "docs/"
    chore: "chore/"
}
@lint {
    @conventional-commit-type {
        enabled: true
        allowed-types: ["feat", "fix", "docs", "refactor", "test", "chore"]
    }
}

Notice how yml2hml automatically converts underscore keys (main_branch_name) to HML’s dash convention (main-branch-name), nested objects become @element blocks, and scalar lists become arrays.

What it handles

Limitations

• Anchors and aliases (&anchor, *alias)
• Complex or multi-line keys
• Merge keys (<<)
• YAML tags (!tag)

Language features used

yml2hml is also a showcase of hica language features:

• Enum types: type YamlLine { YKeyVal(...), YListItem(...), ... } for classifying parsed lines
• Structs: struct ConvertState { remaining: list<string> } for parser state
• Slice patterns: [" ", ..rest] => for counting indentation
• Or-patterns: "true" | "yes" | "on" => for YAML boolean mapping
• Pattern matching: match/Some/None throughout for safe value handling
• String interpolation: "@{hkey} \{" for building output
• Recursion: convert_block recursively processes nested YAML structure
• Pipe operator: read_file(path) |> unwrap for chaining
• Closures: map(items, (item) => hml_value(strip(item))) for transformations
• Dot-call syntax: trimmed.strip(), items.length() for readability
• File I/O: read_file, write_file with Result error handling
• CLI prelude: cli() |> arg() builder for --help, --version, and argument validation
• CLI args: cli_parse, Parsed(r), get_positional for structured argument handling

Source

The full source is in programs/yml2hml.hc (~580 lines).