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
10 use ast::*;
11
factor(rule: Rule) -> Rule12 pub fn factor(rule: Rule) -> Rule {
13 match rule {
14 Rule { name, ty, expr } => Rule {
15 name,
16 ty,
17 expr: expr.map_top_down(|expr| {
18 // TODO: Use box syntax when it gets stabilized.
19 match expr {
20 Expr::Choice(lhs, rhs) => match (*lhs, *rhs) {
21 (Expr::Seq(l1, r1), Expr::Seq(l2, r2)) => {
22 if l1 == l2 {
23 Expr::Seq(l1, Box::new(Expr::Choice(r1, r2)))
24 } else {
25 Expr::Choice(
26 Box::new(Expr::Seq(l1, r1)),
27 Box::new(Expr::Seq(l2, r2)),
28 )
29 }
30 }
31 (lhs, rhs) => Expr::Choice(Box::new(lhs), Box::new(rhs)),
32 },
33 expr => expr,
34 }
35 }),
36 },
37 }
38 }
39