Solution for Golang Tour No 58

gistfile1.go

package main

import (
    "fmt"
    "math"
)

// type declaration
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)
    } else {
		z := float64(100)
		s := float64(0)
    	for math.Abs(s - z) > 0.000001 {
            s = z
			z = z - (z*z - x)/(2*z)
		}
		return z, nil
	}
}

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