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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 list(rule: Rule) -> Rule {
let Rule { name, ty, expr } = rule;
Rule {
name,
ty,
expr: expr.map_bottom_up(|expr| {
// TODO: Use box syntax when it gets stabilized.
match expr {
Expr::Seq(l, r) => match *l {
Expr::Rep(l) => {
let l = *l;
match l {
Expr::Seq(l1, l2) => {
// Converts `(rule ~ rest)* ~ rule` to `rule ~ (rest ~ rule)*`,
// avoiding matching the last `rule` twice.
if l1 == r {
Expr::Seq(l1, Box::new(Expr::Rep(Box::new(Expr::Seq(l2, r)))))
} else {
Expr::Seq(Box::new(Expr::Rep(Box::new(Expr::Seq(l1, l2)))), r)
}
}
expr => Expr::Seq(Box::new(Expr::Rep(Box::new(expr))), r),
}
}
expr => Expr::Seq(Box::new(expr), r),
},
expr => expr,
}
}),
}
}
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