package main

import (
	"fmt"
)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
	return fmt.Sprintf("cannot Sqrt negative number: %v", float64(e))
}

func Sqrt(x float64) (float64, error) {
	if x < 0 {
		return 0, ErrNegativeSqrt(x)
	}	
	precision := 0.00001
	old_z := 0.0
	z := x
	iter := 0
	for (z - old_z) > precision {
		iter += 1
		old_z := z
		z -= (z*z - x) / (2*z)
		if old_z - z < 0 {
			if ((old_z - z) * -1) < precision {
				fmt.Println("Required precision has been reached after", iter, "iterations! Square root of", x , "is", z)
				return z, nil
			}
		} else if (old_z - z) < precision {
			fmt.Println("Required precision has been reached after", iter, "iterations! Square root of", x , "is", z)
			return z, nil
		}
	}
	return z, nil
}

func main() {
	fmt.Println(Sqrt(2))
	fmt.Println(Sqrt(-2))
}