use std::fs::{self, ReadDir};
use std::error::Error;
use std::result::Result;

fn traverse(dirs: &[String]) {
    let res: Vec<Result<ReadDir, &str>> = dirs
        .iter()
        .flat_map(|dirname| {
            let r: Result<ReadDir, &str> = fs::read_dir(dirname).map_err(|e| {e.description()});
            r
        }).collect();
}