December 7th Monday

Oh!  My god.  I made a mistake.

 

io:format("request=~p, state=~p ~n", [Response, NewState]).

 

The above statement is right.  However, you must notice the last argument is a list, I wrote the following.

 

io:format("request=~p, state=~p ~n", Response, NewState).

 

The habit is from the function printf() in C language.