Copy your Sqrt function from the earlier exercises and modify it to return an error value.

Sqrt should return a non-nil error value when given a negative number, as it doesn't support complex numbers.

Create a new type

type ErrNegativeSqrt float64

and make it an error by giving it a

func (e ErrNegativeSqrt) Error() string

method such that ErrNegativeSqrt(-2).Error() returns "cannot Sqrt negative number: -2".

Note: a call to fmt.Print(e) inside the Error method will send the program into an infinite loop. You can avoid this by converting e first:fmt.Print(float64(e)). Why?

Change your Sqrt function to return an ErrNegativeSqrt value when given a negative number.

package main

import (
    "fmt"
    "strconv"
)
type ErrNegativeSqrt float64
func (e ErrNegativeSqrt) Error() string{
    if e < 0 {
        return "cannot Sqrt negative number:" + strconv.FormatFloat(float64(e),'f',5,64)
    }
    return ""
}
func Sqrt(f float64) (float64, error) {
    var e error
    if f < 0 {
        return 0,ErrNegativeSqrt(f)
    }
    var z float64 = 1
    for i := 0; i < 10; i++ {
        z = z - (z*z - f) / (2 * z)
    }
    return z,e
}

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