Types of generated data constructors for dictionaries

[pepe]

Solved, thanks for your help Simon.
I was assuming that dataConRepType would return a core type, i.e. with  
the predicates translated to actual dictionaries. With that assumption  
out of the way, everything fits in its place.

pepe

On 28/08/2008, at 15:50, Simon Peyton-Jones wrote:

> > class Eq a => Eq2 a where eq :: a -> a -> Bool
>
>
> Based on the runtime representation above, I expect the type of  
> Main.:DEq2 to be
>
> Main.:DEq2 :: GHC.Base.:TEq a -> (a -> a -> Bool) -> Main.:TEq2 a
>
>
> but GHC tells me, via (fmap dataConRepType . tcLookupDatacon), the  
> following
>
> Main.:DEq2 :: (a -> a -> Bool) -> Main.:TEq2 a
>
> Why does the type of :DEq2 differ from what :print sees at runtime ?
>
>
>
> Are you sure it’s different?  Here’s what I get (below). Note the  
> type of :DEq2.
>
> Can you tell me how to reproduce what you are seeing?
>
> Simon
>
>
> module Foo where
> class Eq a => Eq2 a where
> op :: a -> a -> Bool
>
>
> ghc -c -ddump-types Foo.hs -dppr-debug
> TYPE SIGNATURES
>     main:Foo.$p1Eq2{v r5P} [gid] :: forall a{tv a5D} [tv].
>                                     (main:Foo.Eq2{tc r5z} a{tv a5D}  
> [tv]) =>
>                                     <pred>base:GHC.Base.Eq{tc 23}  
> a{tv a5D} [tv]
>     main:Foo.:DEq2{v r5R} [gid] :: forall a{tv a5D} [tv].
>                                    (base:GHC.Base.Eq{tc 23} a{tv  
> a5D} [tv]) =>
>                                    (a{tv a5D} [tv] -> a{tv a5D} [tv]  
> -> base:GHC.Base.Bool{(w) tc 3c})
>                                    -> (main:Foo.:TEq2{tc r5Q}) a{tv  
> a5D} [tv]
>     main:Foo.op{v r5B} [gid] :: forall a{tv a5D} [tv].
>                                 (main:Foo.Eq2{tc r5z} a{tv a5D}  
> [tv]) =>
>                                 a{tv a5D} [tv] -> a{tv a5D} [tv] ->  
> base:GHC.Base.Bool{(w) tc 3c}
> TYPE CONSTRUCTORS
>     data (:TEq2{tc}) a
>         RecFlag NonRecursive
>         Generics: no
>         = :DEq2{d} :: forall a.
>                       base:GHC.Base.Eq{tc 23} a =>
>                       (a -> a -> base:GHC.Base.Bool{(w) tc 3c}) - 
> > :TEq2{tc} a
>               Stricts: _
>         FamilyInstance: none
> Tycons with generics:
> Dependent modules: []
> Dependent packages: [base]
> bash-3.2$