Changes to Data.Typeable

Yitzchak Gale gale at
Sun Jul 10 09:51:03 CEST 2011

Simon Marlow wrote:
> In response to this ticket:
> ...
> === Proposed API changes ===
> 1. DEPRECATE mkTyCon...
> 2. Add
>   mkTyCon3 :: String -> String -> String -> TyCon
> ...Most users can just derive Typeable, there's no need
> to use mkTyCon3.
> In due course we can rename mkTyCon3 back to mkTyCon.

Anecdotally, it seems to me that many, if not most,
packages on Hackage that create Typeable instances
do so using mkTyCon, not by deriving Typeable.
There seems to be some standard boilerplate that
spreads virally from one library to the next.

Perhaps it would be worth checking to what extent
mkTyCon is used on Hackage. If this is as widespread
as I suspect, even a simple deprecation warning could
have a cascading effect on typical output from cabal


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