Comma quibbling is a task originally set by Eric Lippert in his blog.



Task

Write a function to generate a string output which is the concatenation of input words from a list/sequence where:

 An input of no words produces the output string of just the two brace characters "{}".
 An input of just one word, e.g. ["ABC"], produces the output string of the word inside the two braces, e.g. "{ABC}".
 An input of two words, e.g. ["ABC", "DEF"], produces the output string of the two words inside the two braces with the words separated by the string " and ", e.g. "{ABC and DEF}".
 An input of three or more words, e.g. ["ABC", "DEF", "G", "H"], produces the output string of all but the last word separated by ", " with the last word separated by " and " and all within braces; e.g. "{ABC, DEF, G and H}".


Test your function with the following series of inputs showing your output here on this page:

 [] # (No input words).
 ["ABC"]
 ["ABC", "DEF"]
 ["ABC", "DEF", "G", "H"]


Note: Assume words are non-empty strings of uppercase characters for this task.




(defun quibble (inputs &optional oxford-comma)
    (define final
        (if (and (caddr inputs) oxford-comma)
            ", and "
            " and " ) )
    (defun comma-quibble (words)
        (cond
            ((null words) "")
            ((null (cdr words)) (car words))
            (t (begin
                (string-append (car words)
                    (if (caddr words)
                        (string-append ", " (comma-quibble (cdr words)))
                        (string-append final (cadr words))) ) ) ) ) )
    (string-append "{" (comma-quibble inputs) "}") )
 
; test cases:
(print (quibble '())) ; empty list
(print (quibble '("ABC")))
(print (quibble '("ABC" "DEF")))
(print (quibble '("ABC" "DEF" "G" "H")))
 
(newline)
 
; test cases using the Oxford comma:
(print (quibble '() t))
(print (quibble '("ABC") t))
(print (quibble '("ABC" "DEF") t))
(print (quibble '("ABC" "DEF" "G" "H") t))