#13581: UNPACK should allow recursion that obviously terminates -------------------------------------+------------------------------------- Reporter: ryanreich | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): No, the reason that GHC can't act on the unpacks is that it processes each `data instance` declaration, once and for all, when it encounters it. So it bahveas much as if it saw {{{ type instance BigWord (Succ n) = BigWord_Succ n data BigWord_Succ n = BigWord {-# UNPACK #-}(BigWord n} {-# UNPACK #-}(BigWord n) }}} At this point it can't unpack those fields because it has no idea what `n` is. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13581#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler