RCL - Ruby-like Configuration Language

A Ruby-like configuration language parser written in Crystal.

Features

• Ruby-like syntax - Simple, readable configuration format
• Standalone parser - Independent library, reusable for any project
• Custom block handlers - Register handlers for specific block types
• Type-safe values - Strings, numbers, booleans, arrays, nested blocks
• Comments - Support for # comments
• Stable AST contract - Document#to_json
• Formatter - Convert parsed AST back to canonical RCL text
• Native conversion - Export to YAML/TOML/HCL
• Named blocks - region "us" do projects to regions.us

Installation

For local development, add dependency from monorepo path:

dependencies:
  rcl:
    path: ./implementations/crystal

Usage

require "rcl"

# Parse a file
doc = RCL.parse_file("config.rcl")

# Parse a string
doc = RCL.parse_string("key = \"value\"")

# Access values
doc.get_string("server.address")
doc.get_int("server.port")
doc.get_bool("feature.enabled")

# Convert to Hash
hash = doc.to_h

# AST JSON
json = doc.to_json

# Format
source = RCL.format(doc)

# Convert
yaml = RCL.to_yaml(doc)
toml = RCL.to_toml(doc)
hcl = RCL.to_hcl(doc)

Named block projection example:

config do
  region "us" do
    name = "My Name"
  end
end

{ "config": { "regions": { "us": { "name": "My Name" } } } }

Constraints:

• Comments: # only
• Strings: double quotes only ("...")
• Bare identifier values are invalid (name = value fails)
• Dotted keys are nested (a.b = 1 -> {a: {b: 1}})
• Duplicate/conflicting key paths fail

Example RCL File

# Server configuration
server do
  address = "example.com"
  port = 8080
  enabled = true
end

# List of features
features = ["auth", "logging", "cache"]

Development

# Install dependencies
cd implementations/crystal && crystal deps

# Run tests
cd implementations/crystal && crystal spec

# Build
cd implementations/crystal && crystal build src/rcl.cr

Implementations

Multi-language workspace is available under implementations/.

• implementations/crystal - Crystal parser + formatter + converters
• implementations/ruby - Ruby parser + formatter
• implementations/typescript - TypeScript parser + formatter
• implementations/go - Go parser + formatter + converters
• implementations/kotlin - Kotlin parser + formatter + converters
• implementations/swift - Swift parser + formatter + converters
• implementations/rust - Rust parser + formatter + converters
• implementations/php - PHP parser + formatter + converters
• implementations/elixir - Elixir parser + formatter + converters
• implementations/ocaml - OCaml parser + formatter + converters
• implementations/julia - Julia parser + formatter + converters
• implementations/c - C parser + formatter + converters
• implementations/cpp - C++ parser + formatter + converters
• implementations/zig - Zig parser + formatter + converters
• implementations/java - Java parser + formatter + converters
• implementations/d - D parser + formatter + converters
• implementations/csharp - C# parser + formatter + converters
• implementations/lua - Lua parser + formatter + converters
• implementations/dart - Dart parser + formatter + converters

License

MIT