class Proc

    def value(x) #wartosc
        self.call(x)
    end

    def f_root(a, b, eps) #miejsca zerowe
        x = (a+b)/2.0
        val = value(x)

        if val >= -eps and val <= eps
            return x
        else
            left = value(a)
            rigth = value(b)

            if left < 0 and val > 0
                return f_root(a,x,eps)
            elsif left > 0 and val < 0
                return f_root(a,x,eps)
            elsif rigth > 0 and val < 0
                return f_root(x,b,eps)
            elsif rigth < 0 and val > 0
                return f_root(x,b,eps)
            elsif value == 0
                return x
            else
                nil
            end
        end
    end

    def derivative(x) #pochodna
        h = 0.00000000001
        return (0.0+value(x+h)-value(x))/h
    end

    def integral(a, b) #calka oznaczona

        sn = 0.0
        n = 1000
        h = (b-a)/n

        for i in 1..n
            yi = value(a + (i-1)*h)
            yi /= 2 if i == 1 or i == n
            sn += h*yi
        end

        return sn
    end

   def plot(a, b, nazwa) #wykres

        file = File.open(nazwa, "w")
        file.puts "%!PS"

        x = 10
        y = 20

        dx = (b - a) / x.to_f
        h = y / 2

        file.puts "0 " + (value(a) + h).to_s + " moveto"

        for i in 1..x
            file.puts i.to_s + " " + (value(a + i * dx) + h).to_s + " lineto"
        end

        file.puts "stroke"
        file.puts "showpage"

        file.close
    end

end

puts "Niech f(x) = x^2"
f = proc { |x| x*x}


puts "f(42) = ", f.value(42)
puts "Miejsce zerowe na [-2,2] : ", f.f_root(-2, 2.0, 0.000000001)
puts "Pochodna w punkcie 42", f.derivative(42)
puts "pole pod wykresem na przedziale [0, 1] : ", f.integral(0.0, 1.0)

f.plot(-10.0, 10.0, "plik.PS")