`define` and `position token`

[andreasabel]

This fails in some backends:

CNil.     Chars ::=                 ;
cSg.      Chars ::= Char            ;
CSnoc.    Chars ::= Chars Dot Char  ;

define    cSg c = CSnoc CNil (Dot ".") c;

position token     Dot '.'          ;

[andreasabel]

Suggested fix:

1. If the AST is not aware of positions, just put an invalid position there (Dot (0,0) ".").

   cSg :: Char -> Chars
   cSg c = CSnoc CNil (Dot ((0,0), ".")) c
   
   newtype Dot = Dot ((C.Int, C.Int), String)

2. In Haskell/Functor, make position tokens polymorphic.

   cSg :: a -> Char -> Chars' a
   cSg a c = CSnoc a (CNil a) (Dot (a, ".")) c
   
   type Dot = Dot' BNFC'Position
   newtype Dot' a = Dot (a, String)
    deriving (C.Eq, C.Ord, C.Show, C.Read, C.Functor, C.Foldable, C.Traversable)