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 crate::ast::*;
11 
rotate(rule: Rule) -> Rule12 pub 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