[BNFC#176] Haskell: Store node position in the AST

When using bnfc to generate haskell code with the --functor option, the
parser will no store the begining position of the corresponding code in
each node. This might be useful, for instance, to report errors.

Note that this is possibly a larger change than it had to be because I
tried something new: instead of generating code by putting together
strings (or the slightly fancier PrettyPrint.Doc), I refactored the code
that makes happy production to generate an AST which is then
pretty-printed. Both the AST types and the pretty printer being of
course generated by BNFC itself! This seems like an obvious thing to do
but for some reason we never did.

The main advantage is that it makes much better use of the type
checker (whene everything is a string, it doesn't mean much that the
type checking passes...).

In addition, you get much cleaner code by getting rid of all the
separators, keywords, symbols and parentheses that are now inserted by the
pretty printer.

source/BNFC.cabal

@@ -118,6 +118,9 @@ Executable bnfc
     BNFC.Backend.Haskell.MkSharedString
     BNFC.Backend.Haskell.HsOpts
     BNFC.Backend.Haskell.Utils
+    BNFC.Backend.Haskell.AbsHappy
+    BNFC.Backend.Haskell.PrintHappy
+
     -- Profile
     BNFC.Backend.HaskellProfile
     BNFC.Backend.HaskellProfile.CFtoHappyProfile

source/src/BNFC/Backend/Haskell/AbsHappy.hs

@@ -0,0 +1,32 @@
+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE DeriveGeneric #-}
+module BNFC.Backend.Haskell.AbsHappy where
+
+-- Haskell module generated by the BNF converter
+
+
+import Data.Data (Data,Typeable)
+import GHC.Generics (Generic)
+newtype Ident = Ident String
+  deriving (Eq, Ord, Show, Read, Data, Typeable, Generic)
+newtype Terminal = Terminal String
+  deriving (Eq, Ord, Show, Read, Data, Typeable, Generic)
+data Production = P Ident Type [RightHandSide]
+  deriving (Eq, Ord, Show, Read, Data, Typeable, Generic)
+
+data RightHandSide = Rhs [Symbol] Expression
+  deriving (Eq, Ord, Show, Read, Data, Typeable, Generic)
+
+data Symbol = NonTerm Ident | QuotedTerm Terminal | IdentTerm Ident
+  deriving (Eq, Ord, Show, Read, Data, Typeable, Generic)
+
+data Expression
+    = EIdent Ident
+    | EPair Expression Expression
+    | EApp Expression Expression
+  deriving (Eq, Ord, Show, Read, Data, Typeable, Generic)
+
+data Type
+    = TIdent Ident | TPair Type Type | TList Type | TApp Type Type
+  deriving (Eq, Ord, Show, Read, Data, Typeable, Generic)
+