Object subclass: Book [
    | title borrowed |

    Book class >> title: aTitle [
        ^self new initialize: aTitle
    ]

    initialize: aTitle [
        title := aTitle.
        borrowed := false.
    ]

    borrow [
        borrowed := true.
    ]

    returnBook [
        borrowed := false.
    ]

    title [
        ^title
    ]
]

Object subclass: Student [
    | name |

    Student class >> name: aName [
        ^self new initialize: aName
    ]

    initialize: aName [
        name := aName.
    ]

    borrow: aBook [
        aBook borrow.
        Transcript show: name , ' borrowed ' , aBook title; cr.
    ]

    return: aBook [
        aBook returnBook.
        Transcript show: name , ' returned ' , aBook title; cr.
    ]
]

| book student |

book := Book title: 'Programming'.
student := Student name: 'Tanaka'.

student borrow: book.
student return: book.