numeric_literal ::=
 [{+ | -}] {integer | real_number}

integer ::=
 digit [digit]...

real_number ::=
 {integer [. integer] | integer . | . integer} 
 [{E | e} [{+ | -}] integer]

character_literal ::=
 { 'character' | ''}

string_literal ::=
 { 'character...' | ''}