fn f(x) {
    return x*x - 4
}

func graph(f, xmin, xmax, xstep) {
    ymin := -1
    ymax := 0

    # find the bounds of y
    x := xmin
    y := 0

    while x < xmax {
        y = f(x)

        if y < ymin {
            ymin = y
        }

        if y > ymax {
            ymax = y
        }

        x = x + 0.1
    }

    # print row by row
    y := ymax
    x = xmin

    while y >= ymin {
        x = xmin
        while x < xmax {
            v := f(x)
            if y - 0.5 < v && v < y + 0.5 {
                # deduce direction (derivative)
                dx := 0.0001
                dy := (f(x+dx) - v) / dx

                if dy > 1 {
                    print("/")
                } else if dy < -1 {
                    print("\")
                } else {
                    print("=")
                }
            } else {
                if -0.05 < x && x < 0.05 {
                    if y == 0 {
                        print("+")
                    } else {
                        print("|")
                    }
                } else if y == 0 {
                        print("-")
                } else {
                    print(" ")
                }
            }

            x = x + xstep
        }
        # new line
        write("")

        y = y - 1
    }

}

graph(f, -5, 5, 0.1)