Re: [Haskell-cafe] Non-derivable Typeable

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 [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 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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