[Hs-Generics] Regular problem

17 Jan 2011

      Hi all,

/(I think something went wrong with my previous email, so if this is 
sent twice, I apologize)
/
Why do self referential structure omit the selector in record entries 
referencing themselves when converting to the regular data structure?

For instance, when splicing the following data structure:

data P = V {v::String} | II {i::Integer} | P { p::P }
   deriving Show

$(deriveAll ''P "PFP")
type instance PF P = PFP

It generates the following code:

         ...generics@haskell.org
         data P_P_ =
         ...
         instance Constructor P_P_ where
             { conName _ = "P"
               conIsRecord _ = True }
         ...
         data P_P_p_ =
         instance Selector P_V_v_ where
             { selName _ = "v" }
         ...
         instance Selector P_P_p_ where
             { selName _ = "p" }
         type PFP = :+: (C P_V_ (S P_V_v_ (K String))) (:+: (C P_II_ (S 
P_II_i_ (K Integer))) (C P_P_ I))
         instance Regular P where
             {         ...generics@haskell.org
                 from II f0 = R (L (C (S (K f0))))
                 from P f0 = R (R (C (I f0)))
                 ...
                 to R L C S K f0 = II f0
                 to R R C I f0 = P f0 }

Why is the selector name in case of a self referencing record omitted? I 
would have expected something like this:

         type PFP = :+: (C P_V_ (S P_V_v_ (K String))) (:+: (C P_II_ (S 
P_II_i_ (K Integer))) (C P_P_ (S P_P_p_ I)))

and likewise:

                 from II f0 = R (L (C (S (K f0))))
                 from P f0 = R (R (C (S (I f0))))
                 ...
                 to R L C S K f0 = II f0
                 to R R C S I f0 = P f0 }

This gives problems when parsing these kind of structure, or am I 
missing something?

kind regards,

Maarten

[Hs-Generics] Regular problem

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