minidice.rb

class Dice
    def [](value)
        raise 'unimplemented'
    end

    def apply(value = nil)
        self[value].floor
    end

    class << self
        def define_semigroup sym
            define_method sym do |rhs|
                if (rhs.is_a? Fixnum)
                    rhs = K.new(rhs)
                end
                Semigroup.new(sym, self, rhs)
            end
        end
    end

    [:+, :-, :*, :/, :**].each do |sym|
        define_semigroup sym
    end

    def d(rhs)
        if (rhs.is_a? Fixnum)
            rhs = K.new(rhs)
        end
        Semigroup.new(:*, self, Dn.new(rhs))
    end
end

class Dice::K < Dice
    def [](value)
        @k
    end

    def initialize k
        @k = k
    end

    def to_s
        @k.to_s
    end
end

class Dice::Dn < Dice
    def initialize n
        @n = n
    end

    def [](value)
        rand(@n[value]) + 1
    end

    def to_s
        "d#{@n}"
    end
end

class Dice::Percent < Dice
    def initialize percent
        @percent = percent
    end

    def [](v)
        v * @percent / 100.0
    end

    def to_s
        "#{@percent}%"
    end
end

class Dice::Semigroup < Dice
    def initialize op, lhs, rhs
        @op = op
        @lhs = lhs
        @rhs = rhs
    end

    def [](v)
        @lhs[v].send(@op, @rhs[v])
    end

    def to_s
        if @op == :* && @rhs.is_a?(Dn)
            "#{@lhs}#{@rhs}"
        else
            "#{@lhs} #{@op} #{@rhs}"
        end
    end
end

class DiceeContext < BasicObject
    class << self
        def define_kdice k
            define_method "_#{k}" do
                Dice::K.new(k)
            end
        end
    end

    for i in 1..99 do
        define_kdice i
    end
end

def dicee &block
    c = DiceeContext.new
    c.instance_exec &block
end