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