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// pest. The Elegant Parser
// Copyright (c) 2018 Dragoș Tiselice
//
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. All files in the project carrying such notice may not be copied,
// modified, or distributed except according to those terms.
use crate::ast::*;
pub fn rotate(rule: Rule) -> Rule {
fn rotate_internal(expr: Expr) -> Expr {
match expr {
// TODO: Use box syntax when it gets stabilized.
Expr::Seq(lhs, rhs) => {
let lhs = *lhs;
match lhs {
Expr::Seq(ll, lr) => {
rotate_internal(Expr::Seq(ll, Box::new(Expr::Seq(lr, rhs))))
}
lhs => Expr::Seq(Box::new(lhs), rhs),
}
}
Expr::Choice(lhs, rhs) => {
let lhs = *lhs;
match lhs {
Expr::Choice(ll, lr) => {
rotate_internal(Expr::Choice(ll, Box::new(Expr::Choice(lr, rhs))))
}
lhs => Expr::Choice(Box::new(lhs), rhs),
}
}
expr => expr,
}
}
let Rule { name, ty, expr } = rule;
Rule {
name,
ty,
expr: expr.map_top_down(rotate_internal),
}
}
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