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Diffstat (limited to 'vendor/pest/src/pratt_parser.rs')
| -rw-r--r-- | vendor/pest/src/pratt_parser.rs | 387 |
1 files changed, 387 insertions, 0 deletions
diff --git a/vendor/pest/src/pratt_parser.rs b/vendor/pest/src/pratt_parser.rs new file mode 100644 index 000000000..be75f7fa4 --- /dev/null +++ b/vendor/pest/src/pratt_parser.rs @@ -0,0 +1,387 @@ +// 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. + +//! Constructs useful in prefix, postfix, and infix operator parsing with the +//! Pratt parsing method. + +use core::iter::Peekable; +use core::marker::PhantomData; +use core::ops::BitOr; + +use alloc::boxed::Box; +use alloc::collections::BTreeMap; + +use crate::iterators::Pair; +use crate::RuleType; + +/// Associativity of an infix binary operator, used by [`Op::infix(Assoc)`]. +/// +/// [`Op::infix(Assoc)`]: struct.Op.html +#[derive(Clone, Copy, Debug, Eq, PartialEq)] +pub enum Assoc { + /// Left operator associativity. Evaluate expressions from left-to-right. + Left, + /// Right operator associativity. Evaluate expressions from right-to-left. + Right, +} + +type Prec = u32; +const PREC_STEP: Prec = 10; + +/// An operator that corresponds to a rule. +pub struct Op<R: RuleType> { + rule: R, + affix: Affix, + next: Option<Box<Op<R>>>, +} + +enum Affix { + Prefix, + Postfix, + Infix(Assoc), +} + +impl<R: RuleType> Op<R> { + /// Defines `rule` as a prefix unary operator. + pub fn prefix(rule: R) -> Self { + Self { + rule, + affix: Affix::Prefix, + next: None, + } + } + + /// Defines `rule` as a postfix unary operator. + pub fn postfix(rule: R) -> Self { + Self { + rule, + affix: Affix::Postfix, + next: None, + } + } + + /// Defines `rule` as an infix binary operator with associativity `assoc`. + pub fn infix(rule: R, assoc: Assoc) -> Self { + Self { + rule, + affix: Affix::Infix(assoc), + next: None, + } + } +} + +impl<R: RuleType> BitOr for Op<R> { + type Output = Self; + + fn bitor(mut self, rhs: Self) -> Self { + fn assign_next<R: RuleType>(op: &mut Op<R>, next: Op<R>) { + if let Some(ref mut child) = op.next { + assign_next(child, next); + } else { + op.next = Some(Box::new(next)); + } + } + + assign_next(&mut self, rhs); + self + } +} + +/// Struct containing operators and precedences, which can perform [Pratt parsing][1] on +/// primary, prefix, postfix and infix expressions over [`Pairs`]. The tokens in [`Pairs`] +/// should alternate in the order: +/// `prefix* ~ primary ~ postfix* ~ (infix ~ prefix* ~ primary ~ postfix*)*` +/// +/// # Panics +/// +/// Panics will occur when: +/// * `pairs` is empty +/// * The tokens in `pairs` does not alternate in the expected order. +/// * No `map_*` function is specified for a certain kind of operator encountered in `pairs`. +/// +/// # Example +/// +/// The following pest grammar defines a calculator which can be used for Pratt parsing. +/// +/// ```pest +/// WHITESPACE = _{ " " | "\t" | NEWLINE } +/// +/// program = { SOI ~ expr ~ EOI } +/// expr = { prefix* ~ primary ~ postfix* ~ (infix ~ prefix* ~ primary ~ postfix* )* } +/// infix = _{ add | sub | mul | div | pow } +/// add = { "+" } // Addition +/// sub = { "-" } // Subtraction +/// mul = { "*" } // Multiplication +/// div = { "/" } // Division +/// pow = { "^" } // Exponentiation +/// prefix = _{ neg } +/// neg = { "-" } // Negation +/// postfix = _{ fac } +/// fac = { "!" } // Factorial +/// primary = _{ int | "(" ~ expr ~ ")" } +/// int = @{ (ASCII_NONZERO_DIGIT ~ ASCII_DIGIT+ | ASCII_DIGIT) } +/// ``` +/// +/// Below is a [`PrattParser`] that is able to parse an `expr` in the above grammar. The order +/// of precedence corresponds to the order in which [`op`] is called. Thus, `mul` will +/// have higher precedence than `add`. Operators can also be chained with `|` to give them equal +/// precedence. +/// +/// ``` +/// # use pest::pratt_parser::{Assoc, Op, PrattParser}; +/// # #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)] +/// # enum Rule { program, expr, int, add, mul, sub, div, pow, fac, neg } +/// let pratt = +/// PrattParser::new() +/// .op(Op::infix(Rule::add, Assoc::Left) | Op::infix(Rule::sub, Assoc::Left)) +/// .op(Op::infix(Rule::mul, Assoc::Left) | Op::infix(Rule::div, Assoc::Left)) +/// .op(Op::infix(Rule::pow, Assoc::Right)) +/// .op(Op::postfix(Rule::fac)) +/// .op(Op::prefix(Rule::neg)); +/// ``` +/// +/// To parse an expression, call the [`map_primary`], [`map_prefix`], [`map_postfix`], +/// [`map_infix`] and [`parse`] methods as follows: +/// +/// ``` +/// # use pest::{iterators::Pairs, pratt_parser::PrattParser}; +/// # #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)] +/// # enum Rule { program, expr, int, add, mul, sub, div, pow, fac, neg } +/// fn parse_expr(pairs: Pairs<Rule>, pratt: &PrattParser<Rule>) -> i32 { +/// pratt +/// .map_primary(|primary| match primary.as_rule() { +/// Rule::int => primary.as_str().parse().unwrap(), +/// Rule::expr => parse_expr(primary.into_inner(), pratt), // from "(" ~ expr ~ ")" +/// _ => unreachable!(), +/// }) +/// .map_prefix(|op, rhs| match op.as_rule() { +/// Rule::neg => -rhs, +/// _ => unreachable!(), +/// }) +/// .map_postfix(|lhs, op| match op.as_rule() { +/// Rule::fac => (1..lhs+1).product(), +/// _ => unreachable!(), +/// }) +/// .map_infix(|lhs, op, rhs| match op.as_rule() { +/// Rule::add => lhs + rhs, +/// Rule::sub => lhs - rhs, +/// Rule::mul => lhs * rhs, +/// Rule::div => lhs / rhs, +/// Rule::pow => (1..rhs+1).map(|_| lhs).product(), +/// _ => unreachable!(), +/// }) +/// .parse(pairs) +/// } +/// ``` +/// +/// Note that [`map_prefix`], [`map_postfix`] and [`map_infix`] only need to be specified if the +/// grammar contains the corresponding operators. +/// +/// [1]: https://en.wikipedia.org/wiki/Pratt_parser +/// [`Pairs`]: ../iterators/struct.Pairs.html +/// [`PrattParser`]: struct.PrattParser.html +/// [`map_primary`]: struct.PrattParser.html#method.map_primary +/// [`map_prefix`]: struct.PrattParserMap.html#method.map_prefix +/// [`map_postfix`]: struct.PrattParserMap.html#method.map_postfix +/// [`map_infix`]: struct.PrattParserMap.html#method.map_infix +/// [`parse`]: struct.PrattParserMap.html#method.parse +/// [`op`]: struct.PrattParserMap.html#method.op +pub struct PrattParser<R: RuleType> { + prec: Prec, + ops: BTreeMap<R, (Affix, Prec)>, + has_prefix: bool, + has_postfix: bool, + has_infix: bool, +} + +impl<R: RuleType> Default for PrattParser<R> { + fn default() -> Self { + Self::new() + } +} + +impl<R: RuleType> PrattParser<R> { + /// Instantiate a new `PrattParser`. + pub fn new() -> Self { + Self { + prec: PREC_STEP, + ops: BTreeMap::new(), + has_prefix: false, + has_postfix: false, + has_infix: false, + } + } + + /// Add `op` to `PrattParser`. + pub fn op(mut self, op: Op<R>) -> Self { + self.prec += PREC_STEP; + let mut iter = Some(op); + while let Some(Op { rule, affix, next }) = iter.take() { + match affix { + Affix::Prefix => self.has_prefix = true, + Affix::Postfix => self.has_postfix = true, + Affix::Infix(_) => self.has_infix = true, + } + self.ops.insert(rule, (affix, self.prec)); + iter = next.map(|op| *op); + } + self + } + + /// Maps primary expressions with a closure `primary`. + pub fn map_primary<'pratt, 'i, X, T>( + &'pratt self, + primary: X, + ) -> PrattParserMap<'pratt, 'i, R, X, T> + where + X: FnMut(Pair<'i, R>) -> T, + R: 'pratt, + { + PrattParserMap { + pratt: self, + primary, + prefix: None, + postfix: None, + infix: None, + phantom: PhantomData, + } + } +} + +type PrefixFn<'i, R, T> = Box<dyn FnMut(Pair<'i, R>, T) -> T + 'i>; +type PostfixFn<'i, R, T> = Box<dyn FnMut(T, Pair<'i, R>) -> T + 'i>; +type InfixFn<'i, R, T> = Box<dyn FnMut(T, Pair<'i, R>, T) -> T + 'i>; + +/// Product of calling [`map_primary`] on [`PrattParser`], defines how expressions should +/// be mapped. +/// +/// [`map_primary`]: struct.PrattParser.html#method.map_primary +/// [`PrattParser`]: struct.PrattParser.html +pub struct PrattParserMap<'pratt, 'i, R, F, T> +where + R: RuleType, + F: FnMut(Pair<'i, R>) -> T, +{ + pratt: &'pratt PrattParser<R>, + primary: F, + prefix: Option<PrefixFn<'i, R, T>>, + postfix: Option<PostfixFn<'i, R, T>>, + infix: Option<InfixFn<'i, R, T>>, + phantom: PhantomData<T>, +} + +impl<'pratt, 'i, R, F, T> PrattParserMap<'pratt, 'i, R, F, T> +where + R: RuleType + 'pratt, + F: FnMut(Pair<'i, R>) -> T, +{ + /// Maps prefix operators with closure `prefix`. + pub fn map_prefix<X>(mut self, prefix: X) -> Self + where + X: FnMut(Pair<'i, R>, T) -> T + 'i, + { + self.prefix = Some(Box::new(prefix)); + self + } + + /// Maps postfix operators with closure `postfix`. + pub fn map_postfix<X>(mut self, postfix: X) -> Self + where + X: FnMut(T, Pair<'i, R>) -> T + 'i, + { + self.postfix = Some(Box::new(postfix)); + self + } + + /// Maps infix operators with a closure `infix`. + pub fn map_infix<X>(mut self, infix: X) -> Self + where + X: FnMut(T, Pair<'i, R>, T) -> T + 'i, + { + self.infix = Some(Box::new(infix)); + self + } + + /// The last method to call on the provided pairs to execute the Pratt + /// parser (previously defined using [`map_primary`], [`map_prefix`], [`map_postfix`], + /// and [`map_infix`] methods). + /// + /// [`map_primary`]: struct.PrattParser.html#method.map_primary + /// [`map_prefix`]: struct.PrattParserMap.html#method.map_prefix + /// [`map_postfix`]: struct.PrattParserMap.html#method.map_postfix + /// [`map_infix`]: struct.PrattParserMap.html#method.map_infix + pub fn parse<P: Iterator<Item = Pair<'i, R>>>(&mut self, pairs: P) -> T { + self.expr(&mut pairs.peekable(), 0) + } + + fn expr<P: Iterator<Item = Pair<'i, R>>>(&mut self, pairs: &mut Peekable<P>, rbp: Prec) -> T { + let mut lhs = self.nud(pairs); + while rbp < self.lbp(pairs) { + lhs = self.led(pairs, lhs); + } + lhs + } + + /// Null-Denotation + /// + /// "the action that should happen when the symbol is encountered + /// as start of an expression (most notably, prefix operators) + fn nud<P: Iterator<Item = Pair<'i, R>>>(&mut self, pairs: &mut Peekable<P>) -> T { + let pair = pairs.next().expect("Pratt parsing expects non-empty Pairs"); + match self.pratt.ops.get(&pair.as_rule()) { + Some((Affix::Prefix, prec)) => { + let rhs = self.expr(pairs, *prec - 1); + match self.prefix.as_mut() { + Some(prefix) => prefix(pair, rhs), + None => panic!("Could not map {}, no `.map_prefix(...)` specified", pair), + } + } + None => (self.primary)(pair), + _ => panic!("Expected prefix or primary expression, found {}", pair), + } + } + + /// Left-Denotation + /// + /// "the action that should happen when the symbol is encountered + /// after the start of an expression (most notably, infix and postfix operators)" + fn led<P: Iterator<Item = Pair<'i, R>>>(&mut self, pairs: &mut Peekable<P>, lhs: T) -> T { + let pair = pairs.next().unwrap(); + match self.pratt.ops.get(&pair.as_rule()) { + Some((Affix::Infix(assoc), prec)) => { + let rhs = match *assoc { + Assoc::Left => self.expr(pairs, *prec), + Assoc::Right => self.expr(pairs, *prec - 1), + }; + match self.infix.as_mut() { + Some(infix) => infix(lhs, pair, rhs), + None => panic!("Could not map {}, no `.map_infix(...)` specified", pair), + } + } + Some((Affix::Postfix, _)) => match self.postfix.as_mut() { + Some(postfix) => postfix(lhs, pair), + None => panic!("Could not map {}, no `.map_postfix(...)` specified", pair), + }, + _ => panic!("Expected postfix or infix expression, found {}", pair), + } + } + + /// Left-Binding-Power + /// + /// "describes the symbol's precedence in infix form (most notably, operator precedence)" + fn lbp<P: Iterator<Item = Pair<'i, R>>>(&mut self, pairs: &mut Peekable<P>) -> Prec { + match pairs.peek() { + Some(pair) => match self.pratt.ops.get(&pair.as_rule()) { + Some((_, prec)) => *prec, + None => panic!("Expected operator, found {}", pair), + }, + None => 0, + } + } +} |