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Created Feb 6, 2019
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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.
package main
import (
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)
return z, nil
func main() {
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