Putting It Together

Let's combine the pieces from the tutorial into a small command-line program: read integers from standard input, then print how many were read, their sum, and the maximum value.

This is closer to the kind of program Rue is trying to make pleasant than a fixed-size algorithm demo. It uses input, parsing, optional values, matching, loops, mutable accumulator state, string concatenation, and println.

The Program

const std = @import("std");

fn read_num() -> std.option.Option(i64) {
    let line = @read_line()?;
    @parse_i64(line)
}

fn main() -> i32 {
    let OptInt = std.option.Option(i64);

    let mut count: i64 = 0;
    let mut sum: i64 = 0;
    let mut max: OptInt = OptInt.None;

    loop {
        match read_num() {
            OptInt.Some(x) => {
                count = count + 1;
                sum = sum + x;
                max = match max {
                    OptInt.None => OptInt.Some(x),
                    OptInt.Some(m) => if x > m { OptInt.Some(x) } else { OptInt.Some(m) },
                };
            },
            OptInt.None => break,
        }
    }

    println("count: " + @to_string(count));
    println("sum: " + @to_string(sum));
    match max {
        OptInt.Some(m) => println("max: " + @to_string(m)),
        OptInt.None => println("max: (no input)"),
    }

    @intCast(count)
}

What It Does

The program reads one line at a time:

• @read_line() returns Option(StrBuf): Some(line) for input, None at EOF.
• @parse_i64(line) returns Option(i64): Some(n) for a valid integer, None for a line that is not an i64.
• The ? operator in read_num returns early with None if either operation fails.

The main loop stops on the first None. That means it reads numbers until end-of-input or the first non-number line.

Running It

Save the program as stats.rue, then run it with the repository wrapper:

printf '7\n5\n1\n' | scripts/rue exec stats.rue

Output:

count: 3
sum: 13
max: 7

This version returns the count as its process exit code, so the sample run exits with status 3 after printing the output above.

The complete checked-in version lives at examples/first/stats.rue.

Current Rough Edges

There is no prelude yet, so Option is not automatically in scope. Import the standard library explicitly with const std = @import("std");, then name the standard-library optional type through that module: std.option.Option(i64). The local OptInt binding is only a short alias for matching on Some and None without repeating the full module-qualified path.

More Examples

The GitHub repository has more examples in the examples/ directory:

• examples/first/stats.rue - Streaming integer statistics
• examples/std/arraybuf_demo.rue - Growable buffers with std.arraybuf.ArrayBuf
• examples/fibonacci.rue - Iterative and recursive Fibonacci
• examples/binary_search.rue - Binary search on a sorted array
• examples/structs.rue - Working with points and rectangles

Next Steps

This program imports std as a module. The next chapter shows the same module system with your own files, including public and private declarations.