Multiple YACC grammars in one program

How do I compile, link and call different YACC grammars using yyparse() in one program?

From stackoverflow Shaya

• Use the -p option for each separate yacc grammar generation

   -p prefix
  
             Use prefix instead of yy as the prefix for all external
             names produced by yacc.  For X/Open compliance, when the
             environment variable _XPG is set, then the -p option will work
             as described in the previous sentence.  If the environment
             variable _XPG is not set, then the -p option will work as
             described below in the -P option.
  

  From epatel