errors.go

/*
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.
*/

package main

import (
  "fmt"
)

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)
  }

  z := x / 2
  prev := z

  for i := 0.0; i < 10; i++ {
    z -= (z * z - x) / (2 * z)
    if z == prev {
      break
    }
    prev = z
  }

  return z, nil
}


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