strings.ContainsRune()

// Package pangram is a small library for checking if a phrase is a pangram
package pangram

import "strings"

// IsPangram checks if a phrase is a pangram
func IsPangram(s string) bool {
	lookup := strings.ToLower(s)
	for chr := 'a'; chr <= 'z'; chr++ {
		if !strings.ContainsRune(lookup, chr) {
			return false
		}
	}
	return true
}

This begins by lowercasing the input by using the strings ToLower() function. Since, for example, A is considered the same letter as a, lowercasing A makes it easier to check if a is in the input.

The runes of a to z are iterated in the for loop. The strings.ContainsRune() function is used to see if the letter is contained in the input string. If not, then the function immediately returns false.

If the loop completes without returning false, then all of the a-z letters are contained in the input string, and the function returns true.