stdin_reader.vala

using GLib;

namespace snuxoll {
    class StdinReader : Object {
    
        public StdinReader () {
            
        }
        
        public bool eof() {
            return stdin.eof();
        }
        
        public string? read_line() {
            var line = new StringBuilder();
            var buffer = new char[1024];
            while ( ( !line.str.has_suffix ("\n") ) || this.eof() ) {
                string chunk = stdin.gets(buffer);
                if (chunk != null) {
                    line.append(chunk);
                } else {
                  return null;
                }
            }
            return line.str;
        }
    
    }
}

sum_application.vala

using GLib;
using snuxoll;

class SumApplication : Object {

    private uint64 total { get; set; }

    public SumApplication() {
        this.total = 0;
    }
    
    public void run() {
        var reader = new StdinReader();
        while ( !stdin.eof() ) {
            var line = reader.read_line();
            if ( line != null ) {
              var nums = line.strip().split(" ");
              foreach(string num in nums) {
                    this.total += num.to_int();
                }
            }
        }
        stdout.printf("Grand Total: %llu\n", total);
    }
    
    static int main(string[] args) {
        var app = new SumApplication();
        app.run();
        return 0;
    }

}