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.




wrds$ = "[]
[""ABC""]
[""ABC"", ""DEF""]
[""ABC"", ""DEF"", ""G"", ""H""]
"
while  word$(wrds$,j+1,chr$(13)) <> ""
  a$ = word$(wrds$,j+1,chr$(13))
  print a$;" ==> ";
  a$ = "{"+mid$(a$,2,len(a$)-2)+"}"
  j = j + 1
  for i = len(a$) to 1 step -1
    if mid$(a$,i,1) = "," then 
       a$ =  left$(a$,i-1) + " and " + mid$(a$,i+2) 
       exit for
    end if
  next i
  print a$
WEND