YumeXi/format

The library provides formatting facilities for MoonBit.

Usage

Formatting

The base module implements basic formatting functions and types.

We can use try_format! to format a string. If you don't want to get an error, you can use format instead. By the way, print can be used to format arguments and print to the console.

For example:

test {
  assert_eq!(format("Hello {}!", ["World"]), "Hello World!")
  assert_eq!(try_format!("Hello {}!", ["World"]), "Hello World!")
}

The formatting syntax is similar to Rust's format! macro and Cpp's std::format function. But we don't support named arguments due to its complexity and the lack of need (MoonBit already has a builtin string interpolation syntax).

To use it for user-defined types, you should implement Formattable trait with format method. We plan to allow custom formatting field to strength the extensibility in the future.

Terminal Styling

The style module provides terminal styling functions and types.

We can use the | operator to compose styles and finally apply it to a string. In the future, we may support styling specifier in the format syntax.

For example:

test {
  @base.print("{}", [fg(@style.Red) | emph(Bold) | "Bold red text"])
}

Pretty Printing

The prettier package provides pretty printing facilities.

We can implement the Prettifiable trait with prettify method to format a value as a document, and using combinator to build up the document.

For example:

test {
  let doc = group(text("hello") + nest(break_with(" , ") + text("world")))
  // Here we overload the `width` parameter to specify the pretty printing width.
  assert_eq!(format("{:6}", doc), "hello\n  world")
}