pest_meta/optimizer/
lister.rs

1// pest. The Elegant Parser
2// Copyright (c) 2018 Dragoș Tiselice
3//
4// Licensed under the Apache License, Version 2.0
5// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
6// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
7// option. All files in the project carrying such notice may not be copied,
8// modified, or distributed except according to those terms.
9
10use crate::ast::*;
11
12pub fn list(rule: Rule) -> Rule {
13    let Rule { name, ty, expr } = rule;
14    Rule {
15        name,
16        ty,
17        expr: expr.map_bottom_up(|expr| {
18            // TODO: Use box syntax when it gets stabilized.
19            match expr {
20                Expr::Seq(l, r) => match *l {
21                    Expr::Rep(l) => {
22                        let l = *l;
23                        match l {
24                            Expr::Seq(l1, l2) => {
25                                // Converts `(rule ~ rest)* ~ rule` to `rule ~ (rest ~ rule)*`,
26                                // avoiding matching the last `rule` twice.
27                                if l1 == r {
28                                    Expr::Seq(l1, Box::new(Expr::Rep(Box::new(Expr::Seq(l2, r)))))
29                                } else {
30                                    Expr::Seq(Box::new(Expr::Rep(Box::new(Expr::Seq(l1, l2)))), r)
31                                }
32                            }
33                            expr => Expr::Seq(Box::new(Expr::Rep(Box::new(expr))), r),
34                        }
35                    }
36                    expr => Expr::Seq(Box::new(expr), r),
37                },
38                expr => expr,
39            }
40        }),
41    }
42}
pest_meta/optimizer/lister.rs

pest_meta/optimizer/
lister.rs
