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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 unroll(rule: Rule) -> Rule {
let Rule { name, ty, expr } = rule;
Rule {
name,
ty,
expr: expr.map_bottom_up(|expr| match expr {
Expr::RepOnce(expr) => Expr::Seq(expr.clone(), Box::new(Expr::Rep(expr))),
Expr::RepExact(expr, num) => (1..num + 1)
.map(|_| *expr.clone())
.rev()
.fold(None, |rep, expr| match rep {
None => Some(expr),
Some(rep) => Some(Expr::Seq(Box::new(expr), Box::new(rep))),
})
.unwrap(),
Expr::RepMin(expr, min) => (1..min + 2)
.map(|i| {
if i <= min {
*expr.clone()
} else {
Expr::Rep(expr.clone())
}
})
.rev()
.fold(None, |rep, expr| match rep {
None => Some(expr),
Some(rep) => Some(Expr::Seq(Box::new(expr), Box::new(rep))),
})
.unwrap(),
Expr::RepMax(expr, max) => (1..max + 1)
.map(|_| Expr::Opt(expr.clone()))
.rev()
.fold(None, |rep, expr| match rep {
None => Some(expr),
Some(rep) => Some(Expr::Seq(Box::new(expr), Box::new(rep))),
})
.unwrap(),
Expr::RepMinMax(expr, min, max) => (1..max + 1)
.map(|i| {
if i <= min {
*expr.clone()
} else {
Expr::Opt(expr.clone())
}
})
.rev()
.fold(None, |rep, expr| match rep {
None => Some(expr),
Some(rep) => Some(Expr::Seq(Box::new(expr), Box::new(rep))),
})
.unwrap(),
expr => expr,
}),
}
}
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