errors.go

/*
Exercise: Errors
Copy your Sqrt function from the earlier exercise 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.Sprint(e) inside the Error method will send the program into an infinite loop. You can avoid this by converting e first: fmt.Sprint(float64(e)). Why?

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

https://tour.golang.org/methods/20
*/


package main

import (
	"fmt"
	"math"
)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
	return "No negativity please"
}

func Sqrt(x float64) (float64, error) {
	if ( x < 0.0 ) {
		return 0, ErrNegativeSqrt(x)
	}
	z := 1.0
	prev_z := 0.0
	for i:=0; math.Abs(prev_z - z) > 0.00001; i++ {
		prev_z = z
		z -= (z*z - x) / (2*z)
		//fmt.Println(z)
	}
	return z, nil
}

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