refactor: simplify the main func

README.asciidoc

@@ -50,7 +50,7 @@ D - Delta
 Reveal the code words for all letters of the alphabet:
 [source,console]
 ----
-$ ./phonetic-letters --all
+$ phonetic-letters --all
 A - Alpha
 B - Bravo
 C - Charlie

phonetic_letters.go

@@ -3,7 +3,6 @@ package main
 import (
 	"flag"
 	"fmt"
-	"os"
 	"strings"
 )
 
@@ -13,27 +12,21 @@ func main() {
 	flag.BoolVar(&all, "all", false, "reveal the code words of all the letters in the English alphabet.")
 	flag.Parse()
 
+	var input string
+
 	if all {
-		fmt.Println(phoneticLetters(fullAlphabet()))
-		return
-	}
-
-	args := flag.Args()
-
-	if len(args) < 1 {
-		fmt.Println("ERROR: expected an argument")
-		os.Exit(1)
-	} else if len(args) == 1 {
-		fmt.Println(phoneticLetters(args[0]))
+		input = fullAlphabet()
 	} else {
-		input := ""
+		args := flag.Args()
 		for i := range args {
 			input = input + args[i]
 		}
-		fmt.Println(phoneticLetters(input))
-	}
 	}
 
+	fmt.Print(phoneticLetters(input))
+}
+
+// phoneticLetters returns a string of all the code words for the given set of letters.
 func phoneticLetters(letters string) string {
 	letters = strings.ToLower(letters)
 
@@ -99,6 +92,7 @@ func phoneticLetters(letters string) string {
 	return b.String()
 }
 
+// fullAlphabet returns a string of all the letters in the alphabet.
 func fullAlphabet() string {
 	return "a b c d e f g h i j k l m n o p q r s t u v w x y z"
 }