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.




$ list = "[]"
$ gosub comma_quibbling
$ write sys$output return_string
$
$ list = "[""ABC""]"
$ gosub comma_quibbling
$ write sys$output return_string
$
$ list = "[""ABC"", ""DEF""]"
$ gosub comma_quibbling
$ write sys$output return_string
$
$ list = "[""ABC"", ""DEF"", ""G"", ""H""]"
$ gosub comma_quibbling
$ write sys$output return_string
$
$ exit
$
$ comma_quibbling:
$ list = list - "[" - "]"
$ return_string = "{}"
$ if list .eqs. "" then $ return
$ return_string = "{" + f$element( 0, ",", list ) - """" - """"
$ if f$locate( ",", list ) .eq. f$length( list ) then $ goto done2
$ i = 1
$ loop:
$  word = f$element( i, ",", list ) - """" - """"
$  if word .eqs. "," then $ goto done1
$  return_string = return_string - "^" + "^," + word
$  i = i + 1
$  goto loop
$ done1:
$ return_string = f$element( 0, "^", return_string ) + " and" + ( f$element( 1, "^", return_string ) - "," )
$ done2:
$ return_string = return_string + "}"
$ return