Exercise: Errors 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 http://tour.golang.org/#56

errors.go

package main

import (
    "fmt"
    "math"
)

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)
    }
    next := float64(1)
    prev := float64(0)
    for math.Abs(next - prev) > .01 {
        prev, next = next, next - (next*next - x)/(2*next)
    }
    return next, nil
}

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

nice implementation!