problem with rust parser using parser-combinators

problem with rust parser using parser-combinators

extern crate parser_combinators;
use parser_combinators::{
	between,
	char,
	digit,
	many,
	many1,
	ParseError,
	parser,
	Parser,
	ParseResult,
	ParserExt,
};

use parser_combinators::primitives::{
	State,
	Stream,
};

#[derive(Debug)]
enum Expr {
	Int(i32),
	Float(f32),
	Pair(Box<Expr>, Box<Expr>),
}

fn expr<I>(input: State<I>) -> ParseResult<Expr, I> where I: Stream<Item=char> {
	let int_parser = many1(digit())
		.map(|i : String|
			Expr::Int(i.parse::<i32>().unwrap())
		);
	let float_parser = many1(digit())
		.skip(char('.'))
		.and(many(digit()))
		.map(|(i, j) : (String, String)|
			Expr::Float((i + "." + &j).parse::<f32>().unwrap())
		);
	let parens_parser = between(char('('), char(')'), parser(expr::<I>).skip(char(',')).and(parser(expr::<I>)))
		.map(|(i, j) : (Expr, Expr)| Expr::Pair(Box::new(i), Box::new(j)));

	float_parser
		.or(int_parser)
		.or(parens_parser)
		.parse_state(input)
}

fn main() {
	let input = "(512,312)";
	// let input = "(512.1,312.1)";

	let result2 : Result<(Expr, &str), ParseError<char>> = parser(expr).parse(input);
	match result2 {
		Ok((value, _remaining_input)) => println!("Result: {:?}, Remain: {:?}", value, _remaining_input),
		Err(err) => println!("Err: {}", err)
	}
}