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