I think I copied the code exactly.. why am I getting nil instead of Title, Heading, and Body

 class Paper
    def intialize(&block)
        yield self if block_given?
    end

    def set_variable
        return Proc.new do |kind, val|
            [kind, val].join(": ")
        end
    end

    def title(value)
        @title = set_variable.call "TITLE", value
    end

    def heading(value)
        @heading = set_variable.call "HEADING", value
    end

    def body(value) 
        @body = set_variable.call "BODY", value
    end
    def display
        puts @title
        puts "------------------"
        puts @heading
        puts "------------------"
        puts @body
        puts "------------------"
    end
end

paper = Paper.new do |p|
    p.title "my awesome paper"
    p.heading "this is my paper"
    p.body "the entire contents of my paper would go here"
end

paper.display