Changes to Typeable

Ian Lynagh igloo at
Wed Oct 3 15:12:42 CEST 2012

On Wed, Oct 03, 2012 at 12:01:15PM +0000, Simon Peyton-Jones wrote:
> * If we do make Typeable instances by default, there are two paths
>    Plan A (easy): make GHC derive Typeable for everything, deprecate
>             all uses of 'deriving Typeable'.  Small downside: some programs
>             that are currently rejected will be accepted.

Do you literally mean "derive Typeable for everything", or do you mean
that Typeable would be available for all types, similar to how seq is?

i.e. would this be valid, or would it complain that it cannot infer
(Typeable a, Typeable b)?:

    f :: a -> Maybe b
    f = Data.Typeable.cast


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