Simplified parse.

collatz/calculator.go

@@ -25,11 +25,10 @@ func NewCalculator(parser *io.Cliargs) Calculator {
 }
 
 func (o Calculator) Collatz() {
-	err := o.parser.Parse()
+	number, err := o.parser.Parse()
 	if err != nil {
 		log.Panicf("Couldn't parse input: %s\n", err)
 	}
-	number := o.parser.GetNumber()
 	fmt.Print(number.Text(10))
 	o.nextNumber(number)
 	fmt.Println()

io/cliargs.go

@@ -10,17 +10,17 @@ type Cliargs struct {
 	value *big.Int
 }
 
-func (arg *Cliargs) Parse() error {
+func (arg *Cliargs) Parse() (*big.Int, error) {
 	args := os.Args[1:]
 	if len(args) != 1 {
-		return errors.New("only expected 1 arg")
+		return nil, errors.New("only expected 1 arg")
 	}
 	num, success := new(big.Int).SetString(args[0], 10)
 	if !success {
-		return errors.New("argument is not an integer")
+		return nil, errors.New("argument is not an integer")
 	}
 	arg.value = num
-	return nil
+	return num, nil
 }
 
 func (arg *Cliargs) GetNumber() *big.Int {