An Answer to A Tour of Go Exercise: Errors

exercise-error.go

package main

import (
	"fmt"
	"math"
)

type ErrNegSqrt float64

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

func Sqrt(x float64) (float64, error) {
	if x < 0 {
		return 0, ErrNegSqrt(x)
	}
	z := 1.0
	for {
		if math.Abs(z - (z - (z*z - x) / (2*x))) < 1e-16 {
			return z, nil
		} else {
			z -= (z*z - x) / (2*x)
		}
	}
}

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

// returns:
// 1.414213562373095 <nil>
// 0 cannot Sqrt negative number: -2