#11723: TYPE 'UnboxedTupleRep is a lie -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- From @RyanGlScott, comment:28:ticket:11471: I notice that there's a single constructor of `RuntimeRep` for unboxed tuples (`UnboxedTupleRep`). Does this mean something like this should be allowed? {{{#!hs {-# LANGUAGE DataKinds #-} {-# LANGUAGE KindSignatures #-} module Example where import Data.Typeable import GHC.Exts data Wat (a :: TYPE 'UnboxedTupleRep) = Wat a }}} Currently, that fails to compile due to a separate GHC panic: {{{ $ /opt/ghc/head/bin/ghc -O2 -fforce-recomp Example.hs [1 of 1] Compiling Example ( Example.hs, Example.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.1.20160317 for x86_64-unknown-linux): unboxed tuple PrimRep Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} But wouldn't this be dangerous anyway? After all, unboxed tuples are supposed to represent arguments on the stack, so couldn't unboxed tuple polymorphic potentially lead to the RTS miscalculating how much data to read? Or am I misreading this? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11723 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler