partial-pretty-printer

This is a pretty printing library for formatting source code in any language.

You provide declarative rules for how to display each sort of node in a document, including line break options, indentation, and coloring. The Partial Pretty Printer prints the document, picking a good layout that fits in your desired line width if possible.

The Partial Pretty Printer is:

• Peephole-efficient: It lets you display just part of a document. If you ask it to print 50 lines in the middle of a 100,000 line document, it can typically do that in ~50 units of work, rather than ~50,000 units of work. This library was designed to support the Synless editor, which needs to re-render a screenfull of document on every keystroke, even if the screen width has changed.

• Fast: Even when printing every line of a document, it can e.g. print ~400,000 lines of JSON per second (excluding terminal IO time).

• Expressive: The combinators that it uses are a variation on Wadler's Prettier Printer. It's therefore about as expressive as other libraries based on Wadler's algorithm, like JS Prettier.

• Flexible: It can apply user-defined styles to the text and use user-defined predicates (like "is this node a comment") to choose between layouts.

• Also secretly a terminal UI library: See the (optional) pane module for how to arrange multiple documents in a window.

There's a demo JSON formatter implemented using the Partial Pretty Printer, which you can try out with:

cargo run --release --example json -- examples/pokemon.json --width 100