Inferred CallStacks expose implicit parameter
It was noticed (in a thread on ghc-devs) that introducing a CallStack-carrying term into the RHS of a let binding in GHCi produces a type which itself carries a callstack.
I could be wrong but as far as I know this is a bug: the solver should never introduce a constraint that the user didn't write; it should merely provide an empty callstack in the event that a callstack constraint can't be solved.
Prelude> let myList = [1, 2, 3 :: Integer] Prelude> let myList' = myList ++ undefined Prelude> :t myList myList :: [Integer] Prelude> :t myList' myList' :: (?callStack::GHC.Stack.Types.CallStack) => [Integer]
|Component||Compiler (Type checker)|