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( comma_quibbling ).
 
-export( [task/0] ).
 
task() -> [generate(X) || X <- [[], ["ABC"], ["ABC", "DEF"], ["ABC", "DEF", "G", "H"]]].
 
 
 
generate( List ) -> "{" ++ generate_content(List) ++ "}".
 
generate_content( [] ) -> "";
generate_content( [X] ) -> X;
generate_content( [X1, X2] ) -> string:join( [X1, "and", X2], " " );
generate_content( Xs ) ->
	[Last, Second_to_last | T] = lists:reverse( Xs ),
	With_commas = [X ++ "," || X <- T],
	string:join(lists:reverse([Last, "and", Second_to_last | With_commas]), " ").
 