Function combine::produce

pub fn produce<Input, F, R>(f: F) -> Produce<Input, F> where
    Input: Stream,
    F: FnMut() -> R, 

Always returns the value produced by calling f.

Can be used when value is unable to be used for lack of Clone implementation on the value.

#[derive(Debug, PartialEq)]
struct NoClone;
let result = produce(|| vec![NoClone])
    .parse("hello world")
    .map(|x| x.0);
assert_eq!(result, Ok(vec![NoClone]));