translation-unit ::= [declaration-seq]
declaration-seq ::= declaration | declaration-seq declaration
declaration ::= block-decl | function-decl | template-decl | explicit-instantiation |
    explicit-specialization | linkage-specification | namespace-defn
block-decl ::= simple-decl | asm-defn | namespace-alias-defn | using-decl | 
    using-directive
simple-decl ::= [decl-specifier-seq] [init-declarator-list] ;
decl-specifier ::= storage-class-specifier | type-specifier | function-specifier | 
    friend | typedef
decl-specifier-seq ::= decl-specifier | decl-specifier-seq decl-specifier
storage-class-specifier ::= auto | register | static | extern | mutable
function-specifier ::= inline | virtual | explicit