define :queue [][
    init: [
        this\items: []
    ]
]

empty?: function [this :queue][
    zero? this\items
]

push: function [this :queue, item][
    this\items: this\items ++ item
]

pop: function [this :queue][
    ensure -> not? empty? this

    result: this\items\0
    this\items: remove.index this\items 0
    return result
]

Q: to :queue []

push Q 1
push Q 2
push Q 3

print ["queue is empty?" empty? Q]

print ["popping:" pop Q]
print ["popping:" pop Q]
print ["popping:" pop Q]

print ["queue is empty?" empty? Q]