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pest is a PEG parser generator with simplicity and speed in mind.
You will need Cargo and Rust, follow the installation instructions to get them.
Add the following to Cargo.toml
:
pest = "0.4"
and in your Rust lib.rs
or main.rs
:
#[macro_use]
extern crate pest;
You can run the calculator example by using cargo run --example calculator
.
pest uses PEG syntax to enable expressive grammar creation.
impl_rdp! {
grammar! {
expression = _{ paren ~ expression? }
paren = { ["("] ~ expression? ~ [")"] }
}
}
let mut parser = Rdp::new(StringInput::new("(()((())())()")));
assert!(parser.expression());
assert!(parser.end());
pest generates a fast parser at compile time through the use of macros, without forcing you to use nightly. Yes, it works on stable (1.9.0+).
Parser generator | Time to parse 272.5 KB of JSON | pest speedup |
---|---|---|
ANTRL 4 | 153,000 μs (+/- 15,000) | 48.12x |
Bison + Flex | 8,761.9 μs (+/- 697) | 2.76x |
pest | 3,178.9 μs (+/- 40.6) | 1.00x |
Tests have been run on an Intel Q8200, 4GB DDR2, Linux 4.6.2 as follows:
- ANTLR 4 [JSON grammar] (https://github.com/antlr/grammars-v4/blob/master/json/JSON.g4) measured with JMH SingleShotTime
- Bison + Flex JSON grammar with string capturing and printing removed
- pest JSON grammar measured with
cargo bench
- simple PEG grammar
- smart error reporting with
atomic
andsilent
rules - precedence climbing rule
- no generation step (one-step compilation)
- fast macro-generated recursive descent parser
- runs on stable Rust
- elegant functional-style
Token
processing
Short comparison with other parsing tools. Please take into consideration that pest is the youngest among them, but is continuously improving.
nom | LALRPOP | pest | |
---|---|---|---|
type | combinator | generator | generator (macros) |
goals | speed, extensibility | usability | simplicity, speed |
grammar | specialized | LR(1) / LALR(1) | PEG |
steps | 1 | 2 | 1 |
code | separate / mixed | mixed | separate |
extensibility | great | great | little |
great for | binary formats | any text | languages |
error reporting | yes | yes | yes |
GitHub additions | ~10K | ~500K | ~6K |
You will need to increase the recursion limit of the crate by adding #![recursion_limit = "x"]
in your lib.rs
or main.rs
. Try different values for x
until it doesn't error anymore. You can start with a value of 200 and go up or down.