# Pretty Printer
This crate defines a
[Wadler-style](http://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf)
pretty-printing API.
Start with the static functions of [PrettyTree](enum.Doc.html).
## Quick start
Let's pretty-print simple sexps! We want to pretty print sexps like
```lisp
(1 2 3)
```
or, if the line would be too long, like
```lisp
((1)
(2 3)
(4 5 6))
```
A _simple symbolic expression_ consists of a numeric _atom_ or a nested ordered _list_ of
symbolic expression children.
```rust
use pretty_print::*;
use SExp::*;
enum SExp {
Atom(u32),
List(Vec<SExp>),
}
impl SExp {
/// Return a pretty printed format of self.
pub fn to_doc(&self) -> PrettyTree {
match self {
Atom(x) => PrettyTree::text(x.to_string()),
List(xs) => PrettyTree::text("(")
.append(PrettyTree::join(xs.into_iter().map(|x| x.to_doc()), PrettyTree::line_or_space()).nest(1).group())
.append(PrettyTree::text(")")),
}
}
/// Return a pretty printed format of self.
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()
}
}
fn main() {
let atom = Atom(5);
assert_eq!("5", atom.to_pretty(10));
let list = List(vec![Atom(1), Atom(2), Atom(3)]);
assert_eq!("(1 2 3)", list.to_pretty(10));
assert_eq!(
"\
(1
2
3)",
list.to_pretty(5)
);
}
```