create a closure depending on a parameter

gistfile1.rs

fn prod<'a,'b>(a:uint) ->  Box<FnMut(&'b[u8]) -> &'b[u8] +'a> {
  box move |&: input: &'b[u8]| -> &'b[u8] {
    input.slice_from(a)
  }
}
fn main() {
  let mut a = prod(2);
  println!("a1: {}", a("abcdefgh".as_bytes()));
  // -> a1: [99, 100, 101, 102, 103, 104]

  println!("a2: {}", a("ghij".as_bytes()));
  // a2: [105, 106]

  let mut b = prod(3);
  println!("b1: {}", b("abcdefgh".as_bytes()));
  // -> a1: [100, 101, 102, 103, 104]
}