1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
// 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 factor(rule: Rule) -> Rule {
let Rule { name, ty, expr } = rule;
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)))
}
}
// Converts `(rule ~ rest) | rule` to `rule ~ rest?`, avoiding trying to match `rule` twice.
// This is only done for atomic rules, because other rule types have implicit whitespaces.
// FIXME: "desugar" implicit whitespace rules before applying any optimizations
(Expr::Seq(l1, l2), r)
if matches!(ty, RuleType::Atomic | RuleType::CompoundAtomic) =>
{
if *l1 == r {
Expr::Seq(l1, Box::new(Expr::Opt(l2)))
} else {
Expr::Choice(Box::new(Expr::Seq(l1, l2)), Box::new(r))
}
}
// Converts `rule | (rule ~ rest)` to `rule` since `(rule ~ rest)`
// will never match if `rule` didn't.
(l, Expr::Seq(r1, r2)) => {
if l == *r1 {
l
} else {
Expr::Choice(Box::new(l), Box::new(Expr::Seq(r1, r2)))
}
}
(lhs, rhs) => Expr::Choice(Box::new(lhs), Box::new(rhs)),
},
expr => expr,
}
}),
}
}
|
