Crate mfmt

mfmt

Meta formatter library in Rust.

mfmt is a language formatter library written in Rust inspired by go fmt. It’s designed to be configuration-free and generous about styling. It simply focuses on aligning indentations.

This library is used in the following projects.

• schemat, the Scheme formatter
• Pen programming language

Install

cargo +nightly add mfmt

Examples

#![feature(allocator_api)]

use indoc::indoc;
use mfmt::{Builder, format, FormatOptions, line};
use std::alloc::Global;

let builder = Builder::new(Global);
let mut string = String::new();

format(
    &builder.sequence([
        "{".into(),
        builder.indent(builder.sequence([line(), "foo".into(), line(), "bar".into()])),
        line(),
        "}".into(),
    ]),
    &mut string,
    FormatOptions::new(4),
)
.unwrap();

assert_eq!(
    string,
    indoc!(
        "
        {
            foo
            bar
        }
        "
    )
    .trim(),
);

Technical notes

Unlike the Wadler’s algorithm or some other formatters like prettier, mfmt does not search the best format given source codes. For example, we do not have any “group” combinator. Instead, we rather give a formatter information to reconstruct the “best” format that is available in the original source codes.

References

• A prettier printer by Philip Wadler

License

The Unlicense

Modules

• utility
  Utilities.

Structs

• Builder
  Document builder.
• FormatOptions
  Format options.

Enums

• Document
  A document.

Functions

• break
  Breaks a document into multiple lines.
• empty
  Creates an empty document.
• flatten
  Flattens a document.
• flatten_if
  Flattens a document if a condition is true.
• format
  Formats a document.
• indent
  Indents a document.
• line
  Creates a new line.
• line_suffix
  Creates a line suffix.
• offside
  Creates a document indented to a current column.
• sequence
  Creates a sequence of documents.