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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 ast::*;
pub fn optimize(rules: Vec<Rule>) -> Vec<Rule> {
rules
.into_iter()
.map(|rule| {
let rotate_right = |expr| {
// TODO: Use box syntax when it gets stabilized.
match expr {
Expr::Seq(lhs, rhs) => {
let lhs = *lhs;
match lhs {
Expr::Seq(ll, lr) => 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) => {
Expr::Choice(ll, Box::new(Expr::Choice(lr, rhs)))
}
lhs => Expr::Choice(Box::new(lhs), rhs)
}
}
expr => expr
}
};
let unroll_loops = |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
};
match rule {
Rule { name, ty, expr } => Rule {
name,
ty,
expr: expr.map_bottom_up(rotate_right)
.map_bottom_up(unroll_loops)
.map_bottom_up(|expr| {
if ty == RuleType::Atomic {
// TODO: Use box syntax when it gets stabilized.
match expr {
Expr::Seq(lhs, rhs) => match (*lhs, *rhs) {
(Expr::Str(lhs), Expr::Str(rhs)) => Expr::Str(lhs + &rhs),
(Expr::Insens(lhs), Expr::Insens(rhs)) => {
Expr::Insens(lhs + &rhs)
}
(lhs, rhs) => Expr::Seq(Box::new(lhs), Box::new(rhs))
},
expr => expr
}
} else {
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
}
})
}
}
})
.collect()
}
#[cfg(test)]
mod tests {
use super::*;
use quote::Ident;
#[test]
fn concat_strings() {
let rules = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::Seq(
Box::new(Expr::Seq(
Box::new(Expr::Str("a".to_owned())),
Box::new(Expr::Str("b".to_owned()))
)),
Box::new(Expr::Seq(
Box::new(Expr::Str("c".to_owned())),
Box::new(Expr::Str("d".to_owned()))
))
)
},
];
let concatenated = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::Str("abcd".to_owned())
},
];
assert_eq!(optimize(rules), concatenated);
}
#[test]
fn unroll_loop_exact() {
let rules = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::RepExact(Box::new(Expr::Ident(Ident::new("a"))), 3)
},
];
let unrolled = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::Seq(
Box::new(Expr::Ident(Ident::new("a"))),
Box::new(Expr::Seq(
Box::new(Expr::Ident(Ident::new("a"))),
Box::new(Expr::Ident(Ident::new("a")))
))
)
},
];
assert_eq!(optimize(rules), unrolled);
}
#[test]
fn unroll_loop_max() {
let rules = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::RepMax(Box::new(Expr::Str("a".to_owned())), 3)
},
];
let unrolled = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::Seq(
Box::new(Expr::Opt(Box::new(Expr::Str("a".to_owned())))),
Box::new(Expr::Seq(
Box::new(Expr::Opt(Box::new(Expr::Str("a".to_owned())))),
Box::new(Expr::Opt(Box::new(Expr::Str("a".to_owned()))))
))
)
},
];
assert_eq!(optimize(rules), unrolled);
}
#[test]
fn unroll_loop_min() {
let rules = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::RepMin(Box::new(Expr::Str("a".to_owned())), 2)
},
];
let unrolled = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::Seq(
Box::new(Expr::Str("a".to_owned())),
Box::new(Expr::Seq(
Box::new(Expr::Str("a".to_owned())),
Box::new(Expr::Rep(Box::new(Expr::Str("a".to_owned()))))
))
)
},
];
assert_eq!(optimize(rules), unrolled);
}
#[test]
fn unroll_loop_min_max() {
let rules = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::RepMinMax(Box::new(Expr::Str("a".to_owned())), 2, 3)
},
];
let unrolled = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::Seq(
/* TODO possible room for improvement here:
* if the sequences were rolled out in the opposite
* order, we could further optimize the strings
* in cases like this.
Box::new(Expr::Str("aa".to_owned())),
Box::new(Expr::Opt(
Box::new(Expr::Str("a".to_owned()))
))
*/
Box::new(Expr::Str("a".to_owned())),
Box::new(Expr::Seq(
Box::new(Expr::Str("a".to_owned())),
Box::new(Expr::Opt(Box::new(Expr::Str("a".to_owned()))))
))
)
},
];
assert_eq!(optimize(rules), unrolled);
}
#[test]
fn concat_insensitive_strings() {
let rules = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::Seq(
Box::new(Expr::Seq(
Box::new(Expr::Insens("a".to_owned())),
Box::new(Expr::Insens("b".to_owned()))
)),
Box::new(Expr::Seq(
Box::new(Expr::Insens("c".to_owned())),
Box::new(Expr::Insens("d".to_owned()))
))
)
},
];
let concatenated = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Atomic,
expr: Expr::Insens("abcd".to_owned())
},
];
assert_eq!(optimize(rules), concatenated);
}
#[test]
fn long_common_sequence() {
let rules = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Silent,
expr: Expr::Choice(
Box::new(Expr::Seq(
Box::new(Expr::Ident(Ident::new("a"))),
Box::new(Expr::Seq(
Box::new(Expr::Ident(Ident::new("b"))),
Box::new(Expr::Ident(Ident::new("c")))
))
)),
Box::new(Expr::Seq(
Box::new(Expr::Seq(
Box::new(Expr::Ident(Ident::new("a"))),
Box::new(Expr::Ident(Ident::new("b")))
)),
Box::new(Expr::Ident(Ident::new("d")))
))
)
},
];
let optimized = vec![
Rule {
name: Ident::new("rule"),
ty: RuleType::Silent,
expr: Expr::Seq(
Box::new(Expr::Ident(Ident::new("a"))),
Box::new(Expr::Seq(
Box::new(Expr::Ident(Ident::new("b"))),
Box::new(Expr::Choice(
Box::new(Expr::Ident(Ident::new("c"))),
Box::new(Expr::Ident(Ident::new("d")))
))
))
)
},
];
assert_eq!(optimize(rules), optimized);
}
}