Hi All I've asked the following question on StackOverflow, but I thought here might be a good place for it also. Sorry for the crosspost but I'm never sure what the best place to ask Haskell questions is: https://stackoverflow.com/questions/73244177/capturing-typeclass-dictionarie... I've copied the StackOverflow post below: --- Below is code that will happily compile (once adding the constraints package). Foo1 and Foo2 are two alternate definitions of Foo, which I can write f1 and f2 sensibly for. However, I *think* Foo3 is reasonable as well. Yet I don't know how to write f3. It seems to me that Haskell should store a pointer to the typeclass dictionary inside the Foo3 constructor, for whatever a is passed when Foo3 is created, so then I should be able to just call silly. Since silly just returns String, it doesn't matter if a has been erased by now, I should be able to happily call the silly pointed to by the dictionary stored in the constructor Foo3. Is my reasoning right? And if so, how can I write f3. Alternative, have I missed something and is there a good reason why I need either Dict or Proxy here because without them I haven't got enough information? {-# LANGUAGE ScopedTypeVariables #-} import Data.Constraint (Dict(Dict), withDict)import Data.Proxy (Proxy) data Aliceclass C a where silly :: Stringinstance C Alice where silly = "Silly Alice" data Foo1 where Foo1 :: Dict (C a) -> Foo1 f1 :: Foo1 -> Stringf1 (Foo1 (dict :: Dict (C a))) = withDict dict $ silly @a data Foo2 where Foo2 :: C a => Proxy a -> Foo2 f2 :: Foo2 -> Stringf2 (Foo2 (_ :: Proxy a)) = silly @a data Foo3 where Foo3 :: C a => Foo3 mkFoo3 :: forall a. C a => Foo3mkFoo3 = Foo3 @a f3 :: Foo3 -> Stringf3 = undefined