#9893: Switching on TypeFamilies extension stops code from typechecking -------------------------------------+------------------------------------- Reporter: phischu | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: x86_64 (amd64) | Unknown/Multiple Difficulty: Unknown | Type of failure: GHC Blocked By: | rejects valid program Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- The following code has the `TypeFamilies` extension enabled but does not use it. It does not typecheck with GHC 7.8.3. If we do not enable `TypeFamilies` (i.e. delete the first line) it typechecks. {{{ {-# LANGUAGE TypeFamilies #-} module ExistentialFamilies where import Control.Monad.ST (runST,ST) un :: () un = runST f where f = return un :: ST s () }}} This happens when trying to compile the program as well as when trying to load it into ghci. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9893 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler