Maybe monad in ruby

gistfile1.rb

class Maybe
    def value
    end
end

class Just < Maybe
    attr_reader :value

    def initialize(value)
        @value = value
    end

    def method_missing(name, *args)
        ret = @value.send(name, *args)
        ret != nil ? just(ret) : nothing
    end

    def ==(other)
        other.class != Nothing && @value == other.value
    end

    def to_s
        "Just #{@value}"
    end
end

class Nothing < Maybe
    def value
        nil
    end

    def method_missing(name, *args)
        nothing
    end

    def ==(_)
        false
    end

    def to_s
        'Nothing'
    end
end

def just(value)
    Just.new value
end

def nothing
    Nothing.new
end

#monad laws
#1
just('hello').upcase == just('hello'.upcase)
#2
just(just(10).value) == just(10)
#3
just('Hello').upcase.downcase == just('hello'.upcase).downcase