lib.rs

//does the monoid operation on the slice of tuples if the closure evaluates to true
fn accumulate<'a, T: Monoid>(tuples: &[(&'a str, &Fn(i32) -> bool)], i: i32) -> Option<T> 
        where &'a str: Into<T> {
		
	tuples.iter()
		.filter(|&&(_,include_fn)| include_fn(i))
		.map(first)
		.fold(None, |acc, concat_str| acc.op(Some(concat_str.into())))
}

fn first<A, B>(&(one, _): (A, B)) -> A {
	one
}