Smalltalk

"WIP"
Object subclass: num_of
[
    | nol |
    <comment: "number of lexemes">

    set_num: number_set
    [
        set_num := number_set
    ]
    get_num
    [
        ^number_set
    ]

    (get_num == 0)
        ifTrue: [^self error: 'Error: NULL' ]

]