#!/usr/bin/ruby

class FIFO(*array) {
    method pop {
        self.empty && die "underflow";
        array.shift;
    };
    method push(*items) {
        array += items;
        self;
    };
    method empty {
        array.len == 0;
    };
};

var f = FIFO();
say f.empty;        # true
f.push('foo');
f.push('bar', 'baz');
say f.pop;          # foo
say f.empty;        # false

var g = FIFO('xxx', 'yyy');
say g.pop;          # xxx
say f.pop;          # bar