Macro fn_block::fn_expr

macro_rules! fn_expr {
    ($return_type:ty : $body:expr) => { ... };
    ($body:expr) => { ... };
}

This macro wraps a given rust code block into a closure and directly calls the closure. Optionally the return type of the closure can be specified first and separeted with a colon from the body expression.

Example without return type:

let o = Some("Foobar");
let s = fn_block!{{
  let foo = o?.get(0..3);
  Some(foo?.to_lowercase())
}};
assert_eq!("foo", s.unwrap());

Example with return type:

use std::str::from_utf8;
use std::error::Error;
struct ConvertErr();
impl <T: Error> From<T> for ConvertErr {
    fn from(_: T) -> ConvertErr {ConvertErr()}
}
let s : &[u8] = &[0x0020,0x0034,0x0032];
let res_int = fn_expr!{ Result<u32,ConvertErr>:
    from_utf8(s)?.trim().parse::<u32>()?.into_ok()
}.unwrap_or(0u32);
assert_eq!(res_int, 42);

Note that the example use the trait IntoOk, defined in this crate.