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.




 
(lib 'match)
 
(define (quibble words)
    (match words
         [ null "{}"]
         [ (a)  (format "{ %a }" a)]
         [ (a b) (format "{ %a and %a }" a b)]
         [( a ... b c) (format "{ %a %a and %a }" (for/string ([w a]) (string-append w ", "))  b c)]
         [else 'bad-input]))
 
 
;; output
 
 (for ([t '(() ("ABC") ("ABC" "DEF") ("ABC" "DEF" "G" "H"))])
    (writeln t '----> (quibble t)))
 
null     ---->     "{}"    
("ABC")     ---->     "{ ABC }"    
("ABC" "DEF")     ---->     "{ ABC and DEF }"    
("ABC" "DEF" "G" "H")     ---->     "{ ABC, DEF, G and H }"    
 