Switch statement

// Package bob is a library for replying to Bob.
package bob

import (
	"strings"
	"unicode"
)

func isShout(phrase string) bool {
	if strings.IndexFunc(phrase, unicode.IsLetter) == -1 {
		return false
	}
	return strings.ToUpper(phrase) == phrase
}

func isQuestion(phrase string) bool {
	return strings.HasSuffix(phrase, "?")
}

func isEmpty(s string) bool {
	return s == ""
}

// Bob replies to what is remarked to Bob.
func Hey(remark string) string {
	remark = strings.TrimSpace(remark)
	if isEmpty(remark) {
		return "Fine. Be that way!"
	}

	question := isQuestion(remark)
	shout := isShout(remark)

	switch true {
	case question && shout:
		return "Calm down, I know what I'm doing!"
	case shout:
		return "Whoa, chill out!"
	case question:
		return "Sure."
	default:
		return "Whatever."
	}
}

In this approach you use a switch statement to test if there is a question or a shout. The switch, with the help of some private functions to evaluate the conditions, returns the right response for a question, shout, shouted question, or for not being a shout or a question.

In the isShout() function, the strings function IndexFunc() is used to ensure there is at least one letter character in the input. If not, the function returns false, because if the input were only "123" it would equal itself uppercased, but without letters it would not be a shout. If the input does contain a letter, the function returns whether the uppercased input is the same as the input. The uppercasing is done by using the ToUpper() function.

In the isQuestion() function, the strings function HasSuffix() is used to determine if the input ends with a question mark.

In the Hey() function, the TrimSpace() function is used to eliminate any whitespace at the ends of the input. If the string has no characters left, it returns the response for saying nothing.

If the string is not empty, the shout and question variables are set.

The question and shout values are tested in a switch. The logical AND operator (&&) is used to check if both question and shout are true. If a switch arm evaluates to true, the appropriate response is returned. If neither question nor shout is true, the default arm of the switch returns the response when the input is neither a question nor a shout.