nom 4.0.0-alpha2

#[macro_use]
extern crate nom;

use nom::digit;

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

named!(unsigned_float <f32>, map_res!(
  map_res!(
    recognize!(
      alt!(
        delimited!(digit, tag!("."), opt!(digit)) |
        delimited!(opt!(digit), tag!("."), digit)
      )
    ),
    str::from_utf8
  ),
  FromStr::from_str
));

named!(float <f32>, map!(
  pair!(
    opt!(alt!(tag!("+") | tag!("-"))),
    unsigned_float
  ),
  |(sign, value): (Option<&[u8]>, f32)| {
    sign.and_then(|s| if s[0] == b'-' { Some(-1f32) } else { None }).unwrap_or(1f32) * value
  }
));

#[test]
fn unsigned_float_test() {
  assert_eq!(unsigned_float(&b"123.456;"[..]), Ok((&b";"[..], 123.456)));
  assert_eq!(unsigned_float(&b"0.123;"[..]),   Ok((&b";"[..], 0.123)));
  assert_eq!(unsigned_float(&b"123.0;"[..]),   Ok((&b";"[..], 123.0)));
  assert_eq!(unsigned_float(&b"123.;"[..]),    Ok((&b";"[..], 123.0)));
  assert_eq!(unsigned_float(&b".123;"[..]),    Ok((&b";"[..], 0.123)));
}

#[test]
fn float_test() {
  assert_eq!(float(&b"123.456;"[..]),  Ok((&b";"[..], 123.456)));
  assert_eq!(float(&b"+123.456;"[..]), Ok((&b";"[..], 123.456)));
  assert_eq!(float(&b"-123.456;"[..]), Ok((&b";"[..], -123.456)));
}