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.




 
MODULE CommaQuibbling;
IMPORT 
  NPCT:Args,
  Strings,
  Out;
 
VAR
  str: ARRAY 256 OF CHAR;
 
  PROCEDURE Do(VAR s: ARRAY OF CHAR);
  VAR
    aux: ARRAY 128 OF CHAR;
    i,params: LONGINT;
  BEGIN
    params := Args.Number() - 1;
    CASE params OF
       0: 
        COPY("{}",s)
      |1:
        Args.At(1,aux);
        Strings.Append("{",s);
        Strings.Append(aux,s);
        Strings.Append("}",s); 
      ELSE
        Strings.Append("{",s);
        FOR i := 1 TO params - 1 DO
          Args.At(i,aux);
          Strings.Append(aux,s);
          IF i # params - 1 THEN 
            Strings.Append(", ",s)
          ELSE 
            Strings.Append(" and ", s) 
          END
        END;
        Args.At(params,aux);
        Strings.Append(aux,s);
        Strings.Append("}",s)
    END;
 
  END Do;
 
BEGIN
  Do(str);
  Out.String(":> ");Out.String(str);Out.Ln
END CommaQuibbling.
 