#12729: Unlifted newtypes via GADTSyntax -------------------------------------+------------------------------------- Reporter: monoidal | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC disallows to define a newtype of an unlifted type (`newtype A = A Int#`). However, this restriction is not enforced when the newtype is defined using GADT syntax: {{{ newtype A where A :: Int# -> A }}} For example, I can derive Show for A and on my machine `main = print (A 0#)` segfaults. Tested on GHC 8.0.1 and master. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12729 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler