Antoine Latter wrote:
It should be pretty easy to write an adapter function of type "String ->
(Show a => a)".
The type needs to be
String -> (exists a. Show a => a)
which is equivalent to
String -> (forall a. Show a => a -> c) -> c
Here is the implementation of the adapter
newtype ExistsShow = E { showE :: String }
instance Show ExistsShow where
show = showE
withShow :: String -> (forall a. Show a => a -> c) -> c
withShow s f = f (E s)
Essentially, the point is that the types are equivalent
ExistsShow == exists a. Show a => a
Best regards,
Heinrich Apfelmus
--
http://apfelmus.nfshost.com
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