Crate pretty

This crate defines a Wadler-style pretty-printing API.

Start with the static functions of Doc.

Quick start

Let’s pretty-print simple sexps! We want to pretty print sexps like

(1 2 3)

or, if the line would be too long, like

((1)
 (2 3)
 (4 5 6))

A simple symbolic expression consists of a numeric atom or a nested ordered list of symbolic expression children.

enum SExp {
    Atom(u32),
    List(Vec<SExp>),
}
use SExp::*;

We define a simple conversion to a Doc. Atoms are rendered as strings; lists are recursively rendered, with spaces between children where appropriate. Children are nested and grouped, allowing them to be laid out in a single line as appropriate.

impl SExp {
    /// Return a pretty printed format of self.
    pub fn to_doc(&self) -> RcDoc<()> {
        match *self {
            Atom(ref x) => RcDoc::as_string(x),
            List(ref xs) =>
                RcDoc::text("(")
                    .append(RcDoc::intersperse(xs.into_iter().map(|x| x.to_doc()), Doc::line()).nest(1).group())
                    .append(RcDoc::text(")"))
        }
    }
}

Next, we convert the Doc to a plain old string.

impl SExp {
    pub fn to_pretty(&self, width: usize) -> String {
        let mut w = Vec::new();
        self.to_doc().render(width, &mut w).unwrap();
        String::from_utf8(w).unwrap()
    }
}

And finally we can test that the nesting and grouping behaves as we expected.

let atom = SExp::Atom(5);
assert_eq!("5", atom.to_pretty(10));
let list = SExp::List(vec![SExp::Atom(1), SExp::Atom(2), SExp::Atom(3)]);
assert_eq!("(1 2 3)", list.to_pretty(10));
assert_eq!("\
(1
 2
 3)", list.to_pretty(5));

Advanced usage

There’s a more efficient pattern that uses the DocAllocator trait, as implemented by BoxAllocator, to allocate DocBuilder instances. See examples/trees.rs for this approach.

Re-exports

• pub use self::block::Affixes;
• pub use self::block::BlockDoc;

Modules

• block
  Document formatting of “blocks” such as where some number of prefixes and suffixes would ideally be layed out onto a single line instead of breaking them up into multiple lines. See BlockDoc for an example

Macros

• docs
  Concatenates a number of documents (or values that can be converted into a document via the Pretty trait, like &str)

Structs

• Arena
  An arena which can be used to allocate Doc values.
• BoxAllocator
• BoxDoc
• DocBuilder
  The DocBuilder type allows for convenient appending of documents even for arena allocated documents by storing the arena inline.
• FmtWrite
  Writes to something implementing std::fmt::Write
• IoWrite
  Writes to something implementing std::io::Write
• PrettyFmt
• RcAllocator
• RcDoc
• RefDoc
  Newtype wrapper for &Doc

Enums

• BuildDoc
  Either a Doc or a pointer to a Doc (D)
• Doc
  The concrete document type. This type is not meant to be used directly. Instead use the static functions on Doc or the methods on an DocAllocator.

Traits

• DocAllocator
  The DocAllocator trait abstracts over a type which can allocate (pointers to) Doc.
• DocPtr
• Pretty
  Trait for types which can be converted to a Document
• Render
  Trait representing the operations necessary to render a document
• RenderAnnotated
  Trait representing the operations necessary to write an annotated document.
• StaticDoc

Type Aliases

• SmallText