"haddest a go" is a colloquial phrase that means to attempt or try something. There are several synonyms that can replace this phrase and convey the same meaning, including: giving it a shot, taking a crack at it, giving it a try, having a stab, taking a swing, making an effort, having a whack, and giving it a bash. These phrases are commonly used in informal conversations and are often accompanied by a positive tone that suggests a willingness to try and not be discouraged by failure. Overall, "haddest a go" is just one of many expressions that can express the act of attempting to do something.