Moclap

Moclap is a prototype CLI argument parser for Mojo. This project was developed as an experiment to explore Mojo's reflection capabilities.

Overview

The core objective of this project was to implement a "struct-first" CLI parser that requires zero manual mapping, similar to clap in rust. By leveraging reflection, the parser inspects the provided configuration struct at compile time and generates the necessary logic to populate it. The config struct must be Defaultable to have defaults values.

Current Prototype State

The parser currently supports:

• Basic Types: String, Bool, Int, UInt.
• Fixed-width Integers: Int8 through Int64, UInt8 through UInt64.
• Floating Point: Float16, Float32, Float64.
• Boolean Toggles: Flags flip the default state of a boolean using bitwise negation (~).
• Help Generation: Automatically generates a help menu based on the struct definition and default values provided in __init__.

Example Usage

from moclap import cli_parse

@fieldwise_init
struct Config(Copyable, Defaultable, Writable):
    var name: String
    var port: Int
    var verbose: Bool
    var timeout: Float64

    fn __init__(out self):
        self.name = "app"
        self.port = 8080
        self.verbose = False
        self.timeout = 30.0

fn main() raises:
    # Generates a parser specialized for the Config struct
    var config = cli_parse[Config]()

    # Use the parsed config
    print(config)

Running the Example

Passing arguments:

mojo example.mojo --name "my-server" --port 9000 --verbose

Viewing the auto-generated help:

mojo example.mojo --help

Output:

Command Line Parser Help (-h or --help)
Usage: [options]

Options:
  --name       : String     (default: app)
  --port       : Int        (default: 8080)
  --verbose    : Bool       (default: False)
  --timeout    : Float64    (default: 30.0)