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
rotate(rule: Rule) -> Rule12 pub fn rotate(rule: Rule) -> Rule {
13 fn rotate_internal(expr: Expr) -> Expr {
14 match expr {
15 // TODO: Use box syntax when it gets stabilized.
16 Expr::Seq(lhs, rhs) => {
17 let lhs = *lhs;
18 match lhs {
19 Expr::Seq(ll, lr) => {
20 rotate_internal(Expr::Seq(ll, Box::new(Expr::Seq(lr, rhs))))
21 }
22 lhs => Expr::Seq(Box::new(lhs), rhs),
23 }
24 }
25 Expr::Choice(lhs, rhs) => {
26 let lhs = *lhs;
27 match lhs {
28 Expr::Choice(ll, lr) => {
29 rotate_internal(Expr::Choice(ll, Box::new(Expr::Choice(lr, rhs))))
30 }
31 lhs => Expr::Choice(Box::new(lhs), rhs),
32 }
33 }
34 expr => expr,
35 }
36 }
37
38 match rule {
39 Rule { name, ty, expr } => Rule {
40 name,
41 ty,
42 expr: expr.map_top_down(rotate_internal),
43 },
44 }
45 }
46