#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).compose(emph(Bold)).compose("Bold red text")])
}

#Pretty Printing

The prettier package provides pretty printing facilities.

We can implement the Pretty trait with prettify method for a type to format values 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!(prettify("{:6}", [doc]), "hello\n  world")
}

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