a little wc-like in rust

wc.rs

#![feature(collections)]

use std::io::prelude::*;
use std::fs::File;
use std::io::BufReader;

fn main() {
    let args: Vec<String> = std::env::args().collect();
    let filename = args[1].clone();

    let file = File::open(&filename).ok().expect("I couldn't open that file, sorry :(");

    let reader = BufReader::new(file);

    let words = reader.split(b' ')
        .map(|x| x.ok().expect("There was an IO error."))
        .count();

    println!("words: {}", words);

    let file = File::open(&filename).ok().expect("I couldn't open that file, sorry :(");

    let newlines = file.bytes()
        .map(|x| x.ok().expect("There was an IO error."))
        .filter(|x| *x == b'\n')
        .count();

    println!("newlines: {}", newlines)
}

I'm wondering why we can access the array at an arbitrary position in line 9. What would happen if the program hadn't received any arguments?

And why do we have to open the same file twice?

I couldn't resist playing golf with that. This is less clear, and less "functional" but is possibly? more efficient and concise:

#![feature(collections)]

use std::io::prelude::*;
use std::fs::File;
use std::io::BufReader;

fn main() {
    let args: Vec<String> = std::env::args().collect();
    let filename = args[1].clone();

    let file = File::open(&filename).ok().expect("I couldn't open that file, sorry :(");

    let reader = BufReader::new(file);

    let mut words = 0;
    let newlines = reader.split(b'\n')
        .map(|x| {
            let line = x.ok().expect("There was an IO error");
            words = words + line.split(|x| *x == b' ').filter(|x| x.len() > 0).count();
            line
        })
        .count();

    println!("words: {}", words);
    println!("newlines: {}", newlines)
}

I'd love to see a Reactive stream version of that (Rx stuff) ...

• one stage to turn the file into lines (map)
  • and a count for that
  • and a second stage that turns the lines into words concat_map (I'm really not sure, I'm just dabbling with Rx so far).
    • and a count for that.

It would be a single pass and would be "functional" (as far as the client code goes).