[Haskell-cafe] Non-derivable Typeable

[Roman Cheplyaka]

It doesn't seem to — am I doing something wrong?

  GHCi, version 7.6.1.20121207: http://www.haskell.org/ghc/  :? for help
  Loading package ghc-prim ... linking ... done.
  Loading package integer-gmp ... linking ... done.
  Loading package base ... linking ... done.
  Prelude> :set -XDeriveDataTypeable -XStandaloneDeriving
  Prelude> :m +Data.Typeable
  Prelude Data.Typeable> data Foo m = Foo (m ())
  Prelude Data.Typeable> deriving instance Typeable1 m => Typeable (Foo m)

  <interactive>:5:1:
      Can't make a derived instance of `Typeable (Foo m)':
        `Foo' must only have arguments of kind `*'
      In the stand-alone deriving instance for
        `Typeable1 m => Typeable (Foo m)'

Roman

* José Pedro Magalhães <jpm at cs.uu.nl> [2013-01-22 13:36:26+0000]
> Won't it derive it with StandaloneDeriving?
> 
> 
> Cheers,
> Pedro
> 
> On Tue, Jan 22, 2013 at 1:28 PM, Roman Cheplyaka <roma at ro-che.info> wrote:
> 
> > I need to declare a Typeable instance for a type which has an argument
> > of kind * -> *. GHC refuses to derive it.
> >
> > What is a recommended way to go about it?
> >
> > In particular, if I write the instance by hand, how important is the
> > fingerprint, and how could I generate it?
> >
> > Roman
> >
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