Rust itself does not have a compose function. But a closure works fine, so `|fname| to_buff_reader(check_err(open_file(fname)))` would work. If you want to go further, a nightly Rust allows for this kind of construction:

    #![feature(unboxed_closures, fn_traits)] // that's why we cannot use stable (yet)
    
    struct Composed<F, G>(pub F, pub G);
    
    impl<F, G, T, U, V> FnOnce<T> for Composed<F, G>
            where F: FnOnce<T, Output=U>, G: FnOnce<(U,), Output=V> {
        type Output = V;
        extern "rust-call" fn call_once(self, args: T) -> V { self.1(self.0.call_once(args)) }
    }
    
    impl<F, G, T, U, V> FnMut<T> for Composed<F, G>
            where F: FnMut<T, Output=U>, G: FnMut<(U,), Output=V> {
        extern "rust-call" fn call_mut(&mut self, args: T) -> V { self.1(self.0.call_mut(args)) }
    }
    
    impl<F, G, T, U, V> Fn<T> for Composed<F, G>
            where F: Fn<T, Output=U>, G: Fn<(U,), Output=V> {
        extern "rust-call" fn call(&self, args: T) -> V { self.1(self.0.call(args)) }
    }
    
    fn main() {
        println!("{}", Composed(|x| x+3, |y| y*4)(5)); // 32
    }