pom 3.4.0

PEG parser combinators using operator overloading without macros.
Documentation 
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use pom::parser::*;

use std::char::{decode_utf16, REPLACEMENT_CHARACTER};
use std::collections::HashMap;
use std::iter::FromIterator;
use std::str::FromStr;

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

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

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

fn string<'a>() -> Parser<'a, char, String> {
	let special_char = sym('\\')
		| sym('/')
		| sym('"')
		| sym('b').map(|_| '\x08')
		| sym('f').map(|_| '\x0C')
		| sym('n').map(|_| '\n')
		| sym('r').map(|_| '\r')
		| sym('t').map(|_| '\t');
	let escape_sequence = sym('\\') * special_char;
	let char_string = (none_of("\\\"") | escape_sequence)
		.repeat(1..)
		.map(String::from_iter);
	let utf16_char = tag("\\u")
		* is_a(|c: char| c.is_digit(16))
			.repeat(4)
			.map(String::from_iter)
			.convert(|digits| u16::from_str_radix(&digits, 16));
	let utf16_string = utf16_char.repeat(1..).map(|chars| {
		decode_utf16(chars)
			.map(|r| r.unwrap_or(REPLACEMENT_CHARACTER))
			.collect::<String>()
	});
	let string = sym('"') * (char_string | utf16_string).repeat(0..) - sym('"');
	string.map(|strings| strings.concat())
}

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

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

fn value<'a>() -> Parser<'a, char, JsonValue> {
	(tag("null").map(|_| JsonValue::Null)
		| tag("true").map(|_| JsonValue::Bool(true))
		| tag("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<'a>() -> Parser<'a, char, JsonValue> {
	space() * value() - end()
}

#[allow(dead_code)]
fn main() {
	let test = r#"
	{
        "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]
        },
        "escaped characters": "\u2192\uD83D\uDE00\"\t\uD834\uDD1E"
    }"#;

	let input: Vec<char> = test.chars().collect();
	println!("{:?}", json().parse(&input));
}