nom 5.0.0-beta3

#[macro_use]
extern crate nom;

use nom::character::streaming::digit1 as 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)));
}