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// pest. The Elegant Parser
// Copyright (c) 2018 DragoČ™ 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 ast::*;
pub fn factor(rule: Rule) -> Rule {
match rule {
Rule { name, ty, expr } => Rule {
name,
ty,
expr: expr.map_top_down(|expr| {
// TODO: Use box syntax when it gets stabilized.
match expr {
Expr::Choice(lhs, rhs) => match (*lhs, *rhs) {
(Expr::Seq(l1, r1), Expr::Seq(l2, r2)) => {
if l1 == l2 {
Expr::Seq(l1, Box::new(Expr::Choice(r1, r2)))
} else {
Expr::Choice(
Box::new(Expr::Seq(l1, r1)),
Box::new(Expr::Seq(l2, r2))
)
}
}
(lhs, rhs) => Expr::Choice(Box::new(lhs), Box::new(rhs))
},
expr => expr
}
})
}
}
}