例如，A * B * C - D + E - F 将返回 C 和 E 作为一对的结果。

示例代码

use pom::parser::*;

let input = b"abcde";
let parser = sym(b'a') * none_of(b"AB") - sym(b'c') + seq(b"de");
let output = parser.parse(input);
assert_eq!(output, Ok( (b'b', vec![b'd', b'e'].as_slice()) ) );

示例 JSON 解析器

extern crate pom;
use pom::parser::*;
use pom::Parser;

use std::collections::HashMap;
use std::str::{self, FromStr};

#[derive(Debug, PartialEq)]
pub enum JsonValue {
	Null,
	Bool(bool),
	Str(String),
	Num(f64),
	Array(Vec<JsonValue>),
	Object(HashMap<String,JsonValue>)
}

fn space() -> Parser<u8, ()> {
	one_of(b" \t\r\n").repeat(0..).discard()
}

fn number() -> Parser<u8, f64> {
	let integer = one_of(b"123456789") - one_of(b"0123456789").repeat(0..) | sym(b'0');
	let frac = sym(b'.') + one_of(b"0123456789").repeat(1..);
	let exp = one_of(b"eE") + one_of(b"+-").opt() + one_of(b"0123456789").repeat(1..);
	let number = sym(b'-').opt() + integer + frac.opt() + exp.opt();
	number.collect().convert(str::from_utf8).convert(|s|f64::from_str(&s))
}

fn string() -> Parser<u8, String> {
	let special_char = sym(b'\\') | sym(b'/') | sym(b'"')
		| sym(b'b').map(|_|b'\x08') | sym(b'f').map(|_|b'\x0C')
		| sym(b'n').map(|_|b'\n') | sym(b'r').map(|_|b'\r') | sym(b't').map(|_|b'\t');
	let escape_sequence = sym(b'\\') * special_char;
	let string = sym(b'"') * (none_of(b"\\\"") | escape_sequence).repeat(0..) - sym(b'"');
	string.convert(String::from_utf8)
}

fn array() -> Parser<u8, Vec<JsonValue>> {
	let elems = list(call(value), sym(b',') * space());
	sym(b'[') * space() * elems - sym(b']')
}

fn object() -> Parser<u8, HashMap<String, JsonValue>> {
	let member = string() - space() - sym(b':') - space() + call(value);
	let members = list(member, sym(b',') * space());
	let obj = sym(b'{') * space() * members - sym(b'}');
	obj.map(|members|members.into_iter().collect::<HashMap<_,_>>())
}

fn value() -> Parser<u8, JsonValue> {
	( seq(b"null").map(|_|JsonValue::Null)
	| seq(b"true").map(|_|JsonValue::Bool(true))
	| seq(b"false").map(|_|JsonValue::Bool(false))
	| number().map(|num|JsonValue::Num(num))
	| string().map(|text|JsonValue::Str(text))
	| array().map(|arr|JsonValue::Array(arr))
	| object().map(|obj|JsonValue::Object(obj))
	) - space()
}

pub fn json() -> Parser<u8, JsonValue> {
	space() * value() - end()
}

fn main() {
	let input = br#"
	{
        "Image": {
            "Width":  800,
            "Height": 600,
            "Title":  "View from 15th Floor",
            "Thumbnail": {
                "Url":    "http://www.example.com/image/481989943",
                "Height": 125,
                "Width":  100
            },
            "Animated" : false,
            "IDs": [116, 943, 234, 38793]
        }
    }"#;

	println!("{:?}", json().parse(input));
}

您可以使用以下命令运行此示例

cargo run --example json

基准测试

生命周期和文件

字符串字面量具有静态生命周期，因此它们可以与从 pom::Parser 导入的静态版本解析器一起工作。从文件读取的输入具有更短的生命周期。在这种情况下，您应该导入 pom::parser::Parser 并在您的解析器函数上声明生命周期。因此

fn space() -> Parser<u8, ()> {
    one_of(b" \t\r\n").repeat(0..).discard()
}

将变为

fn space<'a>() -> Parser<'a, u8, ()> {
    one_of(b" \t\r\n").repeat(0..).discard()
}