Bison and Flex do not stop when reached EOF, only say "Reading a token:" and wait for input

Well, I've searched my problem for quite a long time and I got nothing. Questions I seen below could not help my situation:

bison end of file

Lex/Flex - Scanning for the EOF character

Flex/Bison EOF propagation from stdin vs a file

END OF FILE token with flex and bison (only works without it)

Situation description:

1. I use Bison and Flex to parse a custome language, say this language's name is MYLAN;

2. in MYLAN syntax, I wrote %start system_decl and system_decl:module_decls{...}; in bison file .ypp, no token denoting "system begin" or "system end" as you can see, the system is simply a comibnation of modules. A file written in MYLAN may look like this:

   module
   ...
   end
   module
   ...
   end
   module
   ...
   end
   

3. the parser worked fine for all the syntax described in .ypp, but when it reached the end of file (it should be EOF but I'm not sure since I tried <<EOF>> but the problem still exists), it could not stop, it keeped wating for a token:

   [MYLANParser] $ ./MYLANParser example.mylan
   ...
   Stack now 0 3
   Entering state 6
   Reducing stack by rule 50 (line 458):
   $1 = nterm module_decls ()
   $2 = nterm module_decl ()
   $$ = nterm module_decls ()
   Stack now 0
   Entering state 3
   Reading a token:
   

It just stuck here and the parser will not stop, anyone can help? Many thanks in advance!