Nom, eating data byte by byte

The goal is to make a parser combinator library that is safe, supports streaming (push and pull), and as much as possible zero copy.

The code is available on Github

Example

#[macro_use]
extern crate nom;

use nom::{IResult,digit,multispace};
use nom::IResult::*;

// Parser definition

use std::str;
use std::str::FromStr;

named!(parens<i64>, delimited!(
    delimited!(opt!(multispace), tag!("("), opt!(multispace)),
    expr,
    delimited!(opt!(multispace), tag!(")"), opt!(multispace))
  )
);

// We transform an integer string into a i64
// we look for a digit suite, and try to convert it.
// if either str::from_utf8 or FromStr::from_str fail,
// the parser will fail
named!(factor<i64>,
  alt!(
    map_res!(
      map_res!(
        delimited!(opt!(multispace), digit, opt!(multispace)),
        str::from_utf8
      ),
      FromStr::from_str
    )
  | parens
  )
);

// we define acc as mutable to update its value whenever a new term is found
named!(term <i64>,
  chain!(
    mut acc: factor  ~
             many0!(
               alt!(
                 tap!(mul: preceded!(tag!("*"), factor) => acc = acc * mul) |
                 tap!(div: preceded!(tag!("/"), factor) => acc = acc / div)
               )
             ),
    || { return acc }
  )
);

named!(expr <i64>,
  chain!(
    mut acc: term  ~
             many0!(
               alt!(
                 tap!(add: preceded!(tag!("+"), term) => acc = acc + add) |
                 tap!(sub: preceded!(tag!("-"), term) => acc = acc - sub)
               )
             ),
    || { return acc }
  )
);

fn main() {
  assert_eq!(expr(&b" 1 +  2 "[..]),             IResult::Done(&b""[..], 3));
  assert_eq!(expr(&b" 12 + 6 - 4+  3"[..]),      IResult::Done(&b""[..], 17));
  assert_eq!(expr(&b" 1 + 2*3 + 4"[..]),         IResult::Done(&b""[..], 11));

  assert_eq!(expr(&b" (  2 )"[..]),              IResult::Done(&b""[..], 2));
  assert_eq!(expr(&b" 2* (  3 + 4 ) "[..]),      IResult::Done(&b""[..], 14));
  assert_eq!(expr(&b"  2*2 / ( 5 - 1) + 3"[..]), IResult::Done(&b""[..], 4));
}